deck_3567302 Flashcards
(500 cards)
1
Q
Term
A
Definition
2
Q
5’ cap
A
a methylated guanine nucleotide added to the 5’ end of eukaryotic mRNA. The cap is necessary to initiate translation of mRNA
3
Q
A band
A
The band of the sarcomere that extends the full length of the thick filament. The A band includes regions of thick and thin filament overlap, as well as a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated apperance. The A band does not shorten during muscle contraction.
4
Q
A site
A
Amino-acyl tRNA site; the site on a ribosome where a new amino acid is added to a growing peptide.
5
Q
Absolute refractory period
A
A period of time following an action potential during which no additional action potential can be evoked regardless of the level of stimulation. (usually because Na+ channel closed whle K+ efflux) z
6
Q
Accessory glands
A
The three glands in the male reproductive system that reproduce semen: the seminal vesicles, the prostate, and the
7
Q
Accessory organs
A
(1) In the GI tract, organs that play a role in digestion but not directly part of the alimentary canal. These include the liver, the gallbladder, the pancreas, adn the salivary glands.
8
Q
Acetyl-CoA
A
The first substrate in teh Krebs cycle, produced primarily from the oxidation of pyruvate by the pyruvate dehydrogenase complex, however acetyl-CoA is also produced during fatty acid oxidation and protein catabolism.
9
Q
Acetylcholine (Ach)
A
The neurotransmitter used throughout the parasympathetic nervous system as well as the neuromuscular junction.
10
Q
Acetylcholinesterase (AChE)
A
The enzyme that breaks down acetylcholine in the synaptic cleft.
11
Q
Acid hydrolases
A
Enzymes that degrade various macromolecules and that require an acidic pH to function properly. Acid hydrolases are found within the lysosomes of cells.
12
Q
Acinar cells
A
Cells that make up exocrine galnds, adn that secrete their products into ducts. For example, in the pancreas, acinar cells secrete digestive enzyme; in the salivary glands, acinar cells secrete saliva.
13
Q
Acrosome
A
A region at the head of a sperm cell that contains digestive enzyems which, when released during the acrosome reaction, can facilitate penetration of the corona radiata of the egg, and subsequently, fertilization
14
Q
Actin
A
A contractile protein. In skeletal and cardiac muscle, actin polymerizes (along with other proteins) to form the thin filaments. Actin is involved in many contractile activities, such as cyotkinesis, pseudopod formation, and muscle contraction.
15
Q
Action potential
A
A localized change in a neruon’s or musce cell’s membrane potential that can propogate itself away from its point of origin. Action potentials are an all-or-none process mediated by the opening of voltage-gated Na+ and K+ channels when the membrane is brought to the threshold potential; opening of the Na+ channels causes a characteristic depolarization, while opening of the K+ channels repolarizes the membrane.
16
Q
Activation energy (Ea)
A
The amount of energy required to produce the transition state of a chemical reaction. If the activation energy for a reaction is very high, the reaction occurs very slowly. Enzymes (and other catalysts) increase reaction rates by reducing activation energy.
17
Q
Active site
A
The 3D site of an enzyme where substrates (reactants) bind and a chemical reaction is facilitated.
18
Q
Active transport
A
The movement of molecules through the plasma membrane against their concentration gradients. Active transport requires input of cellular energy, often in the form of ATP. An example is the Na+/K+ ATPase in the plasma membrane of all cells.
19
Q
Adenine
A
One of the four aromatic bases found in DNA and RNA; also a component of ATP, NADH, and FADH2. Adenine is a purine; it pairs with thymine (in DNA) and with uracil (in RNA)
20
Q
Adenohypophis
A
anterior pituitary gland
21
Q
Adipocyte
A
fat cell
22
Q
Adrenal medulla
A
The inner region of the adrenal gland. The adrenal medulla is part of the sympathetic nervous systme, and releases epinephrine (adrenaline) and norepinephrine into the blood when stimuated. These hormones augment and prolon the effects of sympathetic stimulation in the body.
23
Q
Adrenergic tone
A
A constant input to the arteries that keeps them somewhat constricted to maintain a basal level of blood pressure.
24
Q
Adrenocoricotropic hormone (ACTH)
A
A trop hormone produced by the anterior pituitary gand that targets the adrenal cortex, stimulating it to relase corisol and aldosterone.
25
Afferent arteriole
The small artery that carries blood toward the capillaries of the glomerulus.
26
Afferent neuron
A neuron that arries information (action potentials) to the central nervous system; a sensory neuron.
27
Albumin
A blood protein produced by the liver. Albumin helps to mantain blood osmotic pressure (oncotic pressure)
28
Aldosterone
The principal mineralocorticoid secreted by teh adrenal cortex. This steroid hormone targets the kidney tubules and increases renal reabsorption of sodium [and excretion of potassium]. (this causes ADH to be secreted & increased water comes out, increasing blood pressure indirectly).
29
Alimentary canal
Also known as the gastrointestinal (GI) tract of the digestive tract, the alimentary canal is the long muscular "tube" that includes the mouth esophagus, somatch, small intesitne, and large intestine.
30
Allele
A version of a gene. For example, the gene may be for eye color, and the allels include those for brown eyes, those for blu e eyes, those green eyes, etc. At most, dploid organsims can posses only two alleles for a given gene, one on each of the two homologous chromosomes.
31
Allosteric regulation
The modifaction of enzyme activity through interactino of molecules with specific sites on the enzyme other than the active site (called allosteric sites)
32
Alveoli
(singular alveolus.) Tiny sacs, with walls only a single cell layer thick found at the end of the respiratory bronchiole tree. Alveoli are the site of gas exchange in the respiratory system.
33
Aminion
A sac filled with fluid (aminotic fluid) that surroudns and protects a developing embryo.
34
Amino Acid
The monomer of a protein; amino acids hae an amio group on one end fo the molecule and a carboxylic acid group on the other, and of the of 2 different side chains.
35
Amino acid acceptor site
The 3' end of a tRNA molecule that binds an amino acid. The nucleotide sequence at this end is CCA
36
Aminoacyl tRNA
A tRNA with an amino acid attached. This is made by an animoacyl-tRNA synthetase specific to the amino acid being attache.d
37
Amphipathic
The characteristics of amolecule that has both polar (hydrophilic) and non-polar hydrophobic) regions, e.g. phospholipids, bile, etc.
38
Amylase
An enzyme that digests starch into disaccharides. Amylase is secreted by salivary glands and by the pancreas.
39
Anabolism
The process of bulidng complex structures out of simpler precursors, e.g. synthesizing protiens from amino acids.
40
Anal sphincter
The valve that controls the release of feces from the recturm. It has an internal part made of smooth muscle (thus involuntary) and an external part made of skeletal muscle (thus voluntary).
41
Analogous structures
Physical structures in two different organism that have funcitonal similarity due to their evoluntion in a common environment, but have different underlying structure. Analogous structures arise from convergent evolution.
42
Anaphase
The third phase of mitosis. During anaphase, replicated chromosmes are split apart at their centromeres (the sister chromatids are separated from each other) and moved to opposite sides of the cell.
43
Anaphase I
The third phase of meiosis I. During anaphase I the rplicated homologous chromosomes are separated (the tetrad is split) and pulled to opposite sides of the cell.
44
Anaphase II
The third phase of meiosis II. During anaphase II the sister chromatids are finally spearated at their centromeres and puled to opposite sides of teh cell. Note that anaphase II is identical to mitotic anaphase, excep the number of chromosmes was reduced by half during meiosis I.
45
Androgens
Mal sex hormones. Testosteron is the primary androgen.
46
Angiotensin
A normal blood protein produced by the liver, angiotensin is converted to angiotensim I by renin (secreted by kidney when blood pressur falls). Angiotensin I si further onverted to angiotensim II by ACE (angiotensin converting enzyme). Angiotensin II is a powerful systemic vasocontrictor ans stimulator of aldosterone relase, both of which result in an increase in blood pressure.
47
Antagonist
Something that acts to oppose the action of something else. For example, muscles that move a join in oppoiste direction are said to be antagonists.
48
Anterioir pituitary gland
Also known as the adenohypophysis, the anterior pituitary is made of gland tissue and makes and secretes six different homrones: FSH, LH, ACTH, prolactin, TSH, and growth hormone. The anterior pituitary is controlled b yreleasing and inhibiting factors from the hypothalamus.
49
Antibody (Ab)
Also called immunoblobins, the antibodies are protiens secreted by B-cells upon activation that bind in a highly specific manner to foreign proteins (such as those found of the surface of pathogens or transplanted tissues). The foreign proteins are called antigens. Antibodies generally do not directly destroy antigens, rather they mark them for destruction through other methods, and can inativate antigens by clumping them together or by convering necessary active sites.
50
Anticodon
A sequence of three nucleotides (found int he anticodon loop of tRNA) that is complementary to a specific codon in mRNA. The codon to which the anticodon is complementary specifies the amino acid that is carried by that tRNA.
51
Antidiuretic hormone (ADH)
Also called vasopressin, this hormone is produced in the hypothalamus and secreted by teh posterior pituitary gland. It tartes teh kidney tubules, increasing their permeability to water, adn thus increasing water retention by the body. Also raises blood pressure by inducing moderate vasoconstriction.
52
Antigen (Ag)
A molecule (usually a protein) capable of initiating an immune repsonse (antibody production).
53
Antigen presenting cell
Cells that possess MHC II (B cells and macrophages) and are able to display bits of ingested antigen on their surface in order to activate T cells. See also "MHC"
54
Antiparallel orientation
The normal configuration of double-stranded DNA in which the 5' end of oen strand is paired with the 3' end of the other
55
Antiporter
A carrier protein that transports two molecules acrss the plasma membrane in opposite directions.
56
Aorta
The largest artery in teh body; the aorta carries oxygenated blood away from the left ventricle of the heart.
57
Appendix
A mass of lymphatic tissue at the befenning of the large intestine that helps trap ingested pathogens.
58
Aqueous humor
A thin, watery fluid found in teh anterior segment of the eye (between the lens and the cornea). THe aqueous humor is constantly produced and drained, adn helps to bring nutrients to the lesn and corena, as well as to remove metabolic wastes
59
Arousal
A function in the reproductive system, controlled by the parasympathetic nervous system, that includes erection (via dilation of erectile arteries) and lubrication.
60
Artery
A blood vessel that carries blood away from the heart chambers. Arteries have muscular walls to regulate blood flow and are typically high-pressure vessles.
61
ATP synthase
A protein complex foudn in the inner membrane of the mitochondira. It is essentially a channel that llows H+ ions to flow from teh intermembrane space to the matrix (down teh gradeint produced by the enyzmes complexes of the electron transport chain); as the H= ions flow through the channel, ATP is synthesized from ADP and Pi
62
Atrioventricular (AV) node
The second major node of the cardiac conduction system (after the SA node). The cardiac impulse is delayed slightly at teh AV node, allowing the ventricles to contract just after the atria contract.
63
Atrioventricular bundle (AV) bundle
Also known as the Bundle of His, this is the first portion of the cardiac conduction system, after the AV node.
64
Atrioventricular valves
The valves in the heart that separte the atria from teh ventricles. The tricuspid valve separates teh right atrium from the right ventricel, and the bicuspid (mitral) valves separates the left atrium from the left ventricle. These valves close at the beginning of systole, preventing the backflow of bloo dfrom ventricles to atria, and producing the first heart sound (lub).
65
Atrium
One of the two small chambers in the heart that receive blood and pass it on to the ventricles. The right atrium receives deoxygenated blood from teh body through the superior and inferiro vena cavae, adn the left atrium receives oxygenated blood from teh lungs through the pulmonary veins.
66
Attachment
The first step in viral infection. Attachemen of a virus to its host is very specific and is also known as adsorption.
67
Auditory tube
The tube that connects the middle ear acity with the pharynx; also known as the Eustachian tube. Its fucntion is to equalize midle ear pressure with atmospheric pressure so that pressure on boths sides of the tympanic membrane is the same.
68
Autoimmune reaction
An immune reaction directed against normal (necessary ) cells.Fo example, diabets melitus (typeI) is an autoimmun reaction directed against teh beta cells of the pancrease (destorying them and preventing insulin secretion) and aginst insulin itself.
69
Autonomic nervous system (ANS)
The division of the periperal nervsous system that innervates and cotnrols the visceral organs (everything but the skeletal muscles). It is also knowns as the involuntary nervous system and an be subdivided into the sympathetic and parasympathetic divisions.
70
Autosome
A chromosome that does not determine gender (is not a sex chromosome). Humans have two sex chromsomes and 22 autosomes.
71
Autotroph
An organism that makes its own, typically using CO2 as a carbon source.
72
Auxotroph
A bacterium that cannon survive on minimal medium (glucose alone) because it lacks the ability to syntheisze a molecule it needs to live (typically an amino acid). Auxotrphs must ave the needed substance (the auxiliary trophic substance) added to their medium in order to survive. The are typically denoted by teh susbstance they require followed by a "-" sign in superscript. For example, a bacterium that cannot syntehisze leucine would be a leucine auxotroph, and would be indicated as leu- (w/ a superscripth, though)
73
Avascular
Lacking a blood supply; cartialge is an example of this
74
Axon
A long projection off the cell body of a neruon down which an action potential can be propagated.
75
B cell
A type of lymphocyte that can recognize (bind to) an antigen adn secrete an antibody specific for that antigen. When activated by binding an antigen, B cells mature into plasma cells (that secreted antibody) and memory cells (that patrol the body for future encounters with that antigen). - must be activated by Helper T cell also, though.
76
Bacilus
A bacterium having a rod-like shaped (plural = bacilli).
77
Bacteriophage
A virus that infects a bacterium.
78
Baroreceptor
A sensory receptor that responds to hcanges in pressure; for example, there are baroreceptors in the carotid arteries and the aortic ach that monitor blood pressure.
79
Basement membrane
A layer of collagen fibers that separates epithelial tissue from connective tisse (example of epithelial cells in digestive tract) - they are actual connective tissue.
80
Basilar membrane
The flexible membrane in teh chochlea that supports the organ of Corti (structure which contains the hearing receptors). The fibers of the basilar membrane are short and stiff near the oval windown and long and fleaxible near the apex of the cochlea. This difference in structure allows the basilar membrane to help trasnduce pitch.
81
Bicarbonate
HCO3-. THis ion results from the dissociation of carbonic acid, together wiht carbonic acid forms the the major blood buffer system. Bicarbonate is also secreted by teh pancreas to neutralize stomach acid in the intestines.
82
Bile
A green fluid made from cholesterol and secreted by teh liver. It is stored and concentrated in the gallbladder. Bile isn an amphipathic molecule that is secreted itno the small intestine when fats are present, adn serves to emulsify the fats for better digestion by lipases.
83
Binary fission
An asexual method of bacterial reproduction that serves only to increase the size of the population; ther is no introduciton of gnetic diversity. THe bacterium simply grows in size until it has doubled its cellular components, then it replicates its genone and splits into two.
84
Bipolar neuron
A neuron with a single axon and a single dendrite, often projecting from opposite sides of the cell body. Bipolar neurons are typically associated with sensory organs; an example is the bipolar neuron in the retina of the eye. - note that one axon may innervate many different muscles, or other things.
85
Blastocyst
A fluid-filled sphere formed about 5 days after fertilization of an ovum that is made up of an outer ring of cells and inner cell mass. THis is the structure that implants in the endometrium of the uterus.
86
Bohr effect
The tendency of certain factors to stablize the hemoglobin in the tense conformation, thus reducing its affinity for oxygen and enhancing the relase of oxygen to the tissues. The factors include increased PCO2, increase temperature, increased bisphosphoglycerate (BPG), and decreased pH. Note that the Bohr effect shifts the oxy-hemolobin saturation curve to the right.
87
Bone marrow
A non-bony material that fills the hollow spaces inside bones. Red bone marrow is found in regiosn of spongy bone and is the site of blood cell (red and white) production. Yellow bone marrow is found in the diaphysis (shaft) of long bones, is mostly flat, and is inactive.
88
Bowman's capsule
The region of the nephron that surrounds the glomerulus. The capsule ollects the plasma that is filtered from teh capillaries in the glomerulus.
89
Bronchioles
Very small air tubes int eh respiratory system (diameter 0.5 - 1.0 mm). The walls of the bronchioles are made of smooth muscle (thus involunatry) to help regulate air flow.
90
Brush border enzymes
Enzymes secreted by the mucosal cells lining the intestine. The brush border enzymes are disaccharides adn dipeptidases taht digest the smallest peptides and carbohydrates into their respective monomers.
91
Bulbourethral galnds
Small paired gland found inferior to the prostate in males and at the posterior end of the penile urethra. They secrete an alkaline mucus on sexual arousal that helps toneutralize any traces of acidic urine the urethra that might be harmful to sperm.
92
Calcitonin
A hormone produced by the C-cells of the thyroid gland that decreases serum calcium levels. It targets teh bones (stimulates osteoblasts), the kidneys (reduces calcium reabsorption), and the small intestine (decreases calcium absorption).
93
Calcitriol
A hormone produced from vitamin D that acts in essentially the same manner as parathyroid hormone.
94
Calmodulin
A cyoplasmic Ca2+-binding protein. Calmodulin is particularly important in smooth muscle cells, where binding of Ca2+ allows calmodulin to activate myosin light-chian kinase, the first step in smooth muscle cell contraction.
95
Canaliculus
Very small tube or channel, such as is found between lacunae (connecting them together) in compact bone.
96
Capacitation
An incrase in the fragility of the membranes of sperm cells when exposed to the female reproductive tract. Capacitation is required sot aht the acrosomal enzymes can be relased to faciliate fertilization.
97
Capilary
The smalles of all blodo vessles, typically having a diamtere just large neough for blood cells to pass through in single file. Capillaries have extremelyu thin walls to faciliate the exchange of material between the blood and the tissues.
98
Capsid
The outer protein coat of a virus (the whole coat)
99
Carbohydrates
Molecules made from monosaccharides that serve as the primary source of cellular energy,. Carbohydrates can also act as cell surface markers (good thing to remember).
100
Carbonic anhydrase
An enzyme present in erythrocytes (as well as in other places) that catalyzes the conversion of CO2 and H2O into carbonic acid (H2CO3).
101
Cardiac conduction system
The specialized cells of the heart that spontaneously initiate action potentials and transmit them to the cardiac muscle cells. The cells of the conduction system are essentially cardiac muscle cells, but lack the contractile fibers of the muscle cells, tus they are able to transmit impulses (action ptnetials) more quickly and efficiently that cardiac muscle tissue. The cardiac conduction system includes the SA node, the internodal tract, he Av node, the AV bundle, the right and left bundle branches, and the Purkinje fibers.
102
Cardiac muscle
The muscle tissue of the heart Cardiac muscle is striated, uninucleate, and under involuntary control (controlled by teh autonomic nervous system). Note also that cardiac muscle is self-stimulatory, and autonomic control serves only to modify the intrinsic rate of contraction.
103
Cardiac output
The volume of blood pumped out of the heart in one minute (vol/min); the product of the stroke volume (vol/beat) and the heart rate (beat/min). Cardiac output is directly proportional to blood pressure**.
104
Carrier protein
An integral membrane protein that undergoes a conformational change to move a molecule from one side of the membrane to another. See also 'uniporter', 'antiporter', and 'symporter'.
105
Cartilage
A strong connective tissue with varying degrees of flexibility. (1) Elastic cartilage is the most flexible, forming structures that reuqire support but also need to bend, such as the epiglottis and outer ear. (2) Hyaline cartilage is more rigid than elastic cartilage, and forms the cartilages of the ribs, the respiratory tract, and all joints. (3) Fibrocartilage is the least flexible of them all, and forms very strong connections, such as the public symphysis and the intervertebral disks.
106
Catabolism
The process of breaking down large molecules into smaller precursors, e.g. digesion of starch into glucose.
107
Catalase
The primary enzyme in peroxisomes; catalse catalyzes the hydrolysis of hydrogen peroxide (H2O2) into water and oxygen.
108
Catalyst
Something that increases the rate of a chemical reaction by reducing the activation energy for that reaction. The free energy of reaction remains unchanged.
109
cDNA
Complementary DNA. DNA produced synthetically by reverse trascribing mRNA. Because of eukaryotic mRNA splicing, cDNA contains no inrons.
110
Cecum
The first part of the large intestine.
111
Cell surface receptor
An integral membrane proteint hat binds extracellular signaling molecules, suchas hormones and peptides.
112
Central canal
The hollow center of an osteon, also known as a Haversian canal. The central canal contains blood vessels, lymphatic vessels, lymphatic vessels, and nerves. Bone is laid down around the central canal in concentric rings called lamellae.
113
Central chemoreceptors
Receptors in the central nervous system that monitor the pH of cerebrospinal luid to help regulate ventilation rate.
114
Central Nervous System
The subdivision of the nervous system consisting of the brain and spinal cord.
115
Centriole
A structure composed of a ring of nine microtube triplets, found in pairs in the MTOC (microtubule organizing center) of a cell. The centrioles duplicate during the cell division, and serve as the organizing center for the mitotic spindle.
116
Centromere
A structure near the middle of eukaryotic chromosomes to which the fibers of the mitotic spindle attach during cell division.
117
Cerebellum
The region of teh brain that coordinates and smooth skeletal muscle activity.
118
Cerebral cortex
the cerebral hemispheres. The cerebral cortex is the conscious mind, and is functionally divided into four pairs of lobes: the frontal lobes, the parietal lobes, the temporal lobes, and the occipital lobes.
119
Cerebrospinal fluid
A clear fluid the circulates around through the brain and spinal cord that helps to physially support teh brain and act as a shock absorber, and taht also exchanges nutrients and wastes with teh brain and spinal cord.
120
Ceruminous gland
A gland that secretes a waxy product, found in the external ear canal.
121
Cervix
The opening to the uterus The ervix is typically plugged with a sticky acidic mucus during non-fertile times (to form a barrier against the entry of pathogens), however during ovulation the mucus becomes more watery and alkaline to facilitate sperm entry.
122
Channel protein
An integral protein that selectively allows molecules across the plasma membrane. See also entries under 'ion channel', 'voltage-gated channel', and 'ligand-gated channel'.
123
Chemical synapse
A type of synapse at which a chemical (a neurotransmitter) is released from teh axon of a neuron into the ysnaptic cleft where it binds to receptors on the next structure in sequence, either another neuron or an organ.
124
Chemoreceptor
A sensory receptor that responds to specific chemicals. Some examples are gustatory (taste) receptors, olfactory (smell) receptors, and central chemoreceptors (responds to pH changes in teh cerebrospinal fluid).
125
Chemotaxis
Movement that is directed by chemical gradients, such as nutrients or toxins. (seen in some bacteria)
126
Chemotroph
An organism that relies on a chemical source of energy (such as ATP) instead of light (which phototrophs).
127
Chief cells
Pepsinogen-secreting cells foudn at teh bottom of the gastric glands
128
Chitin
A poysaccharide found in the cell walls of fungi and in the exoskeletons of insects.
129
Cholecystokinin (CCK)
A hormone secreted by the samll intestine (duodenum) in response to the presence of fats. It promotes release of bile from the gallbladder and pancreatic juice from the pancreas,and reduces stomach motility.
130
Cholesterol
A large, ring shaped lipid found in cell membranes. Cholesterol is the precursor for steroid hormones, and is used to manufacture bile salts.
131
Chondrocyte
A mature, cartilage cell.
132
Chorion
The portion of the placenta derived from the zygote.
133
Choroid
The darkly pigmented middle layer of the eyeball, found between teh sclera (outer layer) and the retina (inner layer).
134
Chromosome
A single piece of double-stranded DNA; part of the genome of an organism. Prokaryotes have circular chromosomes and eukaryotes have linear chromosomes.
135
Chylomicron
A type of lipoprotein; the form in which absorbed fats from the intestines are transported to the circulatory system.
136
Chyme
Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.
137
Chymotrypsin
One of the main pancreatic proteases; it is activated (from chymotrypsinogen) by trypsin.
138
Cilia
A hair-like structure on teh cell surface composed of microtubules ina '9+2' arrangement (nine pairs of microtubles surrounding 2 single microtubules in the center). Teh microtubules are conneted with a contractile protien called dynein. Cilia beat in a repetitive sweeping motion, which helps to move substances along the surface of the cell. They are particularly important in the respiratory system, where they sweep mucus out of the trachea and up to the mouth and nose.
139
Ciliary muscles
Muscles that help focus light on teh retin by controlling the curvature of the lens of the eye.
140
Circular smooth muscles
The inner layer of smooth muscle in the wall of the digestive tract. When the circular muscle contracts, the tube diameter is reduced. Certain areas of the circular muscle are thickened to act as valves (sphincters).
141
Clathrin
A fibrous protein found on the intracellular side of the plasma membrane (also associated with the Golgi complex) that helps invaginate the membrane. Typically cel surface receptors are associated with clathrin-coated pits at the plasma membrane binding of the ligan to the receptor trigger invagination (example: cholesterol uptake via lipoprotein endocytosis).
142
Cleavage
The rapid mitotic division of a zygot that being within 24-36 hours after fertilization
143
Coccus
A bacteria having a round shape (plural = cocci)
144
Cochlea
The curled structure in the inner ear that contains the membranes and hair cells that transduce sound waves into action potentials.
145
Codominance
A situation in which a heterozygote displays the phenotype associated with each of the alleles, e.g., human blood type AB.
146
Codon
A group of three nucleotides taht is specific for a particular amino acid, or that specifies 'stop translating'
147
Coenzyme
An **organic molecuel taht associates non-covalently with an enzyme, and that is required for the proper functioning of the enzyme.
148
Cofactor
An **inorganic molecule that associates non-covalently with an enzyme and that is required for the proper functioning of the enzyme
149
Collagen
A protein fiber with a unique triple-helix that gives it great strength. Tissues with a lot of collagen fibers are typically very strong, e.g. bone, tendons, ligaments, etc.
150
Collecting duct
The portion of the nephron where water reabsorption is regulated via antidiuretic hormone (ADH). Several nephrons empty into each collecting duct, and this is the final region through which urine must passon its way to the ureter.
151
Common bile duct
The duct that carries bile from the gallbladder and liver to the small intestine (duodenum).
152
Compact bone
A dense, hard type of bone constructed from osteons (at the microscopic level). Compact bone forms the diaphysis of the the long bones, and the outer shell of the epiphyses and all other bones.
153
Competitive inhibitor
An enzyme inhibitor that competes with substrate for binding at the active site of teh enzyme. When the inhibitor is bound, no product can be made.
154
Complement system
A group of blood proteins that bind non-specifically to the surface proteins of foreign cells (such as bacteria), ultimately leading to the destruction of the foreign cell - part of the innate immunity.
155
Cones
Photoreceptors in the retina of the eye that responds to bright light and provide color vision.
156
Conjugation
A form of genetic recombination in bacteria in which plasmid and/or genomic DNA is transferred from one bacterium to the toher through a conjugation bridge.
157
Connective tissue
One of the four basic tissue types in the body (epithelial, connective, muscle, and nervous). Connective tissue is a supportive tissue consisting of a relatively few cells scattered among a great deal of extracellular material (matrix), and includes adipose tissue (fat), bone, cartilage, the dermis of teh skin, tendons, ligaments, and blood.
158
Convergent evolution
A form of evolution in which different organisms are placed into the same environment and exposed to teh same selection pressures. This causes the organisms to evolve along similar lines. As a result, they may share functional, but not structural similarity (because they possessed different startgin materials). Convergent evolution produces analogous structures.
159
Cooperativity
A type of substrate binding to a multi-active site enzyme, in which the bnidng of one substrate molecule facilitates teh binding of subsequent substrate molecules. A graph of reaction rate vs. substrate concentration appears sigmoidal. Noe that cooperativity can be foudn in other situations as well, for example, hemoglobin bind oxygen cooperatively.
160
Cornea
The clear portion of the tough outer layer of teh eye ball, found over the iris and pupil
161
Corona radiata
The layer of granulosa cells taht surround an oocyte after is has been ovulated.
162
Coronary vessels
The blood vessels taht carry blood to and from cardiac muscle. The coronary arteries branch off teh aorta and carry oxygenated blood to the cardiac tissue. The coronary veins collect deoxygenated blood from teh cardiac tissue, merge to form teh coronary sinus, and drain into the right atrium.
163
Corpus callosum
The largest bundle of white matter (axons) connecting th two cerebral hemispheres.
164
Corpus luteum
Yellow body.' The remnants of an ovarian follicle after ovulation has occurred. The cells enlarge and begin secreting progesterone, the dominant female hormone during the second half of the menstrual cycle. Some estrogen is also secreted.
165
Cortex
The outer layer of an organ, e.g. the renal cortex, the ovarian cortex, the adrenal cortex, etc.
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Corticosteroids
Steroid hormones secreted from the adrenal cortex. The two major classes are teh mineralocorticoids and glucocorticoids. Aldosterone is the principal mineralocorticoid, and cortisol is the principal glucorcorticoid.
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Cortisol
The principal glucocorticoid secreted from teh adrenal cortex. This steroid hormone is released ruing stress, causing increased blood glucose levels and reducing inflammation. The latter effect has led to a clinical use of cortisol as an anti-inflammatory agent.
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Creatine Phosphate
An energy storage molecule used by muscle tissue. The phosphate from creatine phosphate can be removed and attached to an ADP to generate ATP quickly.
169
Cristae
The folds of the inner membrane of a mitochondrion
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Cross bridge
The connection of a mosin head group to an actin filament during muscle contraction (the sliding filament theory).
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Crossing over
The exchange of DNA between paired homologus chromosomes (tetrads) during *prophase I* of meiosis.
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Cyclic AMP (cAMP)
A cyclic version of adenosine monophosphate, where the phosphate is esterified to both the 5' and 3' carbons, forming a ring. Cyclic AMP is an important intracellular signaling moelcule, often called the 'second messenger.' It serves to activate cAMP-dependent kinases, which regulates the activity of other enzymes in the cell. Levels of cAMP are in part regulated by adenylyl cyclase, the enzyme that makes cAMP, adn the activity of adenylyl cyclase i ultimately controlled by the binding of various ligands to cell surface receptors.
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Cytokinesis
The phase of mitosis during which the cell physically splits into two daugter cells. Cytokinesis begins near the end of anaphase, and is completed during telophase.
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Cytosine
One of the four aromatic bases found in DNA and RNA. Cytosine is a pyrimidine; it pairs with guanine.
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Dendrite
A projection of the cell body of a neuron that recieves a nerve impulse form a different neuron and send the impulse to the cell body. Neurons can have one or several dendrites!
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Dense connective tissue
Connective tissue with large amounts of either collagen fibers (making them strong) or elastic fibers, or both. Dense tissues are typically strong (e.g. bone, cartilage, tendons, etc.)
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Depolarization
The movement of teh membrane potential of a cell away from rest potential in a more positive direction.
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Dermis
A layer of connective tissue underneath the epidermis of the skin. The dermis contains blood vessels, lymphatic vessels, nerves, sensory receptors, and glands.
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Desmosome
A general cell junction, used primarily for adhesion.
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Determination
The point during development at which a cell becomes committed to a particular fate (sensory, other, etc.). Note that the cell is not differentiated at this point; determination comes before differentiation. Determination can be due to cytoplasmic effects or to induction by neighboring cells.
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Diaphragm
The primary muscle of inspiration. The diaphragm is stimulated to contract at regular intervals by the respiratory center in the medulla oblongata (via the phrenic nerve). Although it is made of skeletal muscle (and can therefore be voluntary controlled), these stimulations occur autonomously.
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Diaphysis
The shaft of a long bone. The diaphysis is hollow and is made entirely from compact bone.
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Diastole
The perio of time during which the ventricles of the heart are relaxed.
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Diastolic pressure
The pressure measured in the arteries while the ventricles are relaxed (during diastole).
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Diencephalon
The portion of theforebrain that includes the thalamus and hypothalamus.
186
Differentiation
The specialization of cell types, especially during the embryonic and fetal development.
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Diffusion
The movement of a particle (the solute) in a solution from its region of high concentration to its region of low concentration ( or down it concentration gradient).
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Diploid organism
An organism that has two copies of its genome it each cell. The paired genomes are said to be homologous.
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Disaccharide
A molecule composed of two monosaccharides. Common disaccharides include maltose, sucrose, and lactose.
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Distal convoluted tubule
The portion of the nephron tubule after the loop of Henle, but before teh collecting duct. Selective reabsorption and secretion occur here, most notably regulated reabsorption of water and sodium.
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Divergent evolution
A form of evolution in which the same organism is placed into different environments with different selection pressures. This causes organisms to evolve differently, to diverge from their common ancestor. The resulting (new) species may share structural (but not necessarily functional) similarity; divergent evolution produces homologous structures.
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DNA polymerase
Also called DNA pol, this is the enzyme that replicates DNA. Eukaryotes have a single version of the enzyme, simply called DNA pol (not need to know much detail); prokaryotes have three versions, called DNA pol I, DNA pol II, and DNA pol III.
193
Dominant
The allele in a heterozygous genotype that is expressed; the phenotype resulting from either a heterozygous genotype or a homozygous dominant genotype.
194
Dorsal root ganglion
A group of sensory neuron cell bodies found just posterior to the spinal cord on either side. A pair of root ganglia exists for each spinal nerve that expands from the spinal cord. The ganglia are part of the peripheral nervous system (PNS).
195
Downstream
Toward the 3' end of an RNA transcript (the 3' end of the DNA coding strand). Stop codons and (in eukaryotes) the pol-A tail are found 'downstream.'
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Duodenum
The first (approximately 5%) of the small intestinte.
197
Dynein
A contractile protein connecting microtubules in the '9+2- arrangement of cilia and eukaryotic flagella. The contraction of dynein produces the characteristic movement of these structures.
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Ectoderm
One of the three primary (embryonic) germ layers formed during gastrulation. Ectoderm ultimately forms external structures such as the skin, hair, nails, and inner linings of the mouth and anus, as well as the entire nervous system.
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Edema
Swelling of tissues, sometimes caused by inflammation letting into many white blood cells (decreasing oncotic pressure at the end of the capillaries & not letting as much water back into capillaries & staying in tissues).
200
Effector organ
The organ that carries out teh command sent along a particular motor neuron
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Efferent arteriole
The small artery that carries blood away from the capillaries of the glomerulus.
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Efferent neuron
A neuron that carries information (action potentials) away from the central nervous system; a motor neuron.
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Ejaculation
A subphase of male orgasm, a reflex reaction triggered by the presence of semen in the urethra. Ejaculation is a series of rhythmic contractions of muscles near teh base of teh penis that increase pressure in the urethra, forcing the semen out.
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Ejection fraction
The fraction of teh end-diastolic volume ejected from the ventricles in a single contraction of teh heart. THe ejection fraction is normally around 60% of the end diastolic volume.
205
Elastin
A fibrous, connective-tissue protein taht has the ability to recoil to its original shape after being stretche.d Elastin is found in great amounts in lung tissue, arterial tissue, skin, and the epiglottis.
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Electrical synapse
A type of syanpse in which the cells are connected by gap junctions, allowing ions (and therefore an action potential) to spread easily from cell to cell, usually in smooth and cardiac muscle. - compared to chemical synapse.
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Electron transport chain
A series of enzyme complexes found along the inner mitochondrial membrane. NADH and FADH2 are oxidized by tehse enzymes; the electrons are shuttled down the chain and are ultimately passed to oxygen and to produce water. The electron energy is used to pump H+ out of the mitochondrial membrane; the resulting H+ gradient is subsequently used to drive the production of ATP.
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Embryonic stage
The period of human development from implantation through 8 weeks of gestation. Gastrulation, neurulation, and organogenesis occur during this time period. The developing baby is known as embryo during this time period.
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Emission
A subphase of male orgasm. Emission is the movement of sperm (via the vas deferens) and semen into the urtehra in prepartion for ejaculation.
210
End plate potential
The depolarzation of the motor end plate on a muscle cell.
211
Endocrine gland
A ductless gland that secretes a hormone into the blood
212
Endocrine system
A systme of ductless glands taht secrete chemical messengers (into) the blood - has to be into the blood.
213
Endocytosis
The uptake of material into a cell, usually by invagination. See also 'phagocytosis', pinocytosis, and receptor-mediated endocytosis..
214
Endoderm
One of the three primary (embryonic) germ layers
215
Endometrial cycle
formed during gastrulation. Endoderm ultimately forms internal structures, such as the inner lining of the GI tract and glandular organs.
216
Endometrium
The 28 days of the menstrual cycle as they apply to the events in the uterus. The endometrial cycle is also known as the uterine cycle, and has the three subphases: menstruation, the proliferative phase, and the secretory phase.
217
Endospore
The inner epithelial lining of the uterus that thickens and develops during the menstrual cycle, into which a fertilized ovum can implant, and which sloughs off during menstration if a pregnancy does not occur.
218
Endosymbitoic theory
the theory that mitochondria and chloroplasts originated as independent unicellular organsims living in symbiosis with larger cells
219
Endotoxin
A normal component of the outer membrane of Gram-negative bacteria. Endotoxins produce extreme immune reactions (septic shock), particularly when many of them enter the circulation at once.
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Enteric nervous system
The nervous system of the gastrointestinal tract. It controls secretion and motility within teh Gi tract, and is linked to the central nervous system.
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Enterogasterone
A hormone secreted by the small intestine (duodenum) in response to the presence of food. It decreases the rate at which chyme leaves the stomach and enters the small intestine.
222
Enterokinase
A duodenal enzyme that activates trypsinogen (from the pancreas) to trypsin.
223
Envelope
A lipid bilayer that surrounds the capsid of an animal virus. the envelope is acquired as teh virus buds out through the plasma membrane of its host cell. Not all annimal viruses possess and envelope.
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Enzyme
A physiological catalyst. Enzymes are usually proteins, although some RNAs have catalytic activity.
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Epidermis
The outermost layer of teh skin. The epidermis is made of epithelial tissue that is constantly dividing at the bottom; teh cells migrate to teh surface (dying along the way) to be sloughed off at the suface.
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Epididymis
A long, coiled duct on the outside of the testis in which sperm mature.
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Epiglottis
A flexible piece of cartilage in the larynx that flips downward to seal teh trachea during swallowing.
228
Epinephrine
A hormone produced and secreted by teh adrenal medulla that prolongs and increases teh effects of the sympathetic nervous system.
229
Epiphyseal plate
A band of carilage (hyaline) found between the diaphysis and epiphyses of long bones during childhood and adolescence. Cell proliferation in the middle of the eiphyseal plate essentially forces teh diaphysis and epiphyses further apart, while the older cartilage at the endes of the plate is replaced with bone. This is waht allows bone growth during childhood. The epiphyseal plate gets thinner and thinner teh older a person gets, until finally it fuses ( the diaphysis and epiphyses connect) in late adolescence, preventing further elongation of teh bones.
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Epiphysis
One of the two ends of long bone (pl: eiphyses). The epiphyses have an outer shell made of compact bone and inner core of spongy bone. The spongy bone is filled with red bone marrow, the stie of blood cell formation.
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Epistasis
A situation in which the expression of one gene prevents expression of all allelic forms of another gene, e.g., the gene for male pattern baldness is epistatic to the hair color gene.
232
Epithelial tissue
One of the four basic tissue types in the body (epithelial, connective, muscle, and nervous). Epithelial tissue is a lining and covering tissue (e.g. skin, the lining of the stomach and intestines, the lining of the urinary tract, etc. ) or a glandular tissue (e.g. the liver, the pancreas, the ovaries, etc.)
233
Epitope
The specific site on an antigenic molecule that binds to a T cell receptor or to an antibody.
234
EPSP
Excitatory postsynaptic potential; a slight depolarization of a postsynaptic cell, bringing the membrane potential of that cell closer to the threshold for an action potential.
235
Erectile tissue
Specialized tissue with a lot of space that can fill with blood upon proper stimulation, causing teh tissue to become firm. Erectile tissue is found in the penis, the clitoris, the labia, and the nipples.
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Erythrocyte
A red blood cell; they are filled with hemoglobin, and teh function of the erythrocytes is to carry oxygen in the blood.
237
Erythropoietin
A hormone produced and released by the kidney that stimulates the production of red blood cells by the bone marrow.
238
Estrogen
The primary female sex hormone. Estrogen stimulates the development of female secondary sex characteristics during puberty, maintains those characteristics during adulthood, stimulates the development of a new uterine lining after menstruation, and stimulates mammary gland development during pregnancy.
239
Euchromatin
DNA that is loosely packed around histones. This DNA is more accessible to enzymes and the genes in euchromatin can be activated if needed.
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Eukaryotic
A cell characterized by the presence of a nucleus and other membrane-bound organelles. Eukaryotes can be unicellular (protists) or multicellular (fungi, plants and animals).
241
Excitation-contraction coupling
The mechanism that ensures tehat skeletal muscle contraction does not occur without neural stimulation (excitation). A trest, cytosolic [Calcium] is low, and the troponin, tropomyosin complex covers the myosin-binding sites on actin. When the muscle is stimulated by a neuron, calcium is released from the sarcoplasmic reticulum into teh cytosol of the muscle cell. Calcium binds to troponin, causing a conformation change in the troponin-tropomyosin complex that shifts it away from the myosin-binding sites. This allows mysoin and actin to interact according to the sliding filament theory.
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Exclusion
The removal ( and usually the activation) of a viral genome from its host's genome.
243
Excretion
The elimination of wastes from the body.
244
Exocrine gland
A gland that secretes its product into a duct, which ultimately carries the product to the surface of the body or into a body cavity. Some examples of exocrine gland and their products are sweat glands (sweat), gastric glands (acid, mucus, protease), the liver (bile), sebaceous glands (oil), and lacrimanl glands (tears).
245
Exocytosis
The secretion of a cellular product to the extracellular medium through a secretory vesicle.
246
Exon
A nucleotide sequence in RNA that contains protein-coding information. Exons are typically separated by introns (intervening sequences) that are spliced out prior to translation.
247
Exotoxin
A toxin that secreted by a bacterium into its surrounding medium that help the bacterium compete with other species. Some exotoxins cause serious disease in humans (botulism, tetanus, diptheria, toxic shock syndrome).
248
Expiration
The movement of air out of the respiratory tract. Expiration can be passive (caused by relaxation of the diaphragm and elastic recoil of the lungs) or active (caused by contraction of the abdominal muscles, which increases intraabdominal pressure and forces the diaphragm up past its normal relaxed position).
249
F (fertility) factor
A bacterial extrachromosal elent that allows the bacterium to initati conjugation. Bacteria that possess teh F factor are known as F+ 'males'.
250
F1 generation
The first generation of offspring from a given genetic cross.
251
Facilitated diffusion
Movement of a hydrophilic molecuel across the plasma membrane of a cell, down its concentration gradient, through a channel, pore, or carrier molecule in the membrane. Because the hydrophilic nature of the molecule, it requires a special path through the lipid bilayer.
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Facultative anaerobe
An organism that will use oxygen (aerobic metabolism) if it is available, and that can ferment (anaerobic metabolism) if it is not.
253
FADH2
The reduced from (carries electrons) of FAD (flavin adenine dinucleotide). this is the other main electron carrier in cellular respiration (NADH is the most common).
254
Fascicle
A bundle of skeletal muscle cells. Fascicles group together to form skeletal muscles.
255
Fast block to polyspermy
The depolarization of the egg plasma membrane upon fertilization, designed to prevent the entry of more than one sperm into the egg.
256
Feedback inhibition
Also called negative feedback, the inhibition of an early step in a series of events by the product of a later step in the series. This has the effect of stopping the series of events when the products are plentiful and the series is unnecesseary. Feedback inhibition is the most common form of regulation in the body, controllin such things as enzyme reactions, hormone levels, blood pressure, body temperature, etc.
257
Fermentation
The reduction of pyruvate to either ethanol or lactate in order to regenerate NAD+ from NADH. Fermentation occurs in the absence of oxygen, and allow glycolysis to continue under those conditions.
258
Fertilization
The fusion of a sperm with an ovum during sexual reproduction. Fertilization typically occurs in the uterine tubes and requires capacitation of the sperm and relase of the acrosomal enzymes. Fertilization is a species-specific process, requiring binding of a sperm protein to an egg receptor.
259
Fetal stage
The period of human development beginning at 8 weeks of gestation and lasting until birth (38-42 weeks of gestation). During this stage the organs formed in the embryonic stage grow and mature. The developing baby is known as a fetus during this time period.
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Fibrinogen
A blood protein essential to blood clotting. The conversion of fibrinogen to its active form (fibrin) is among the final steps in clot formation, and is triggered by thrombin.
261
Fibroblast
A generic connective tissue cell that produces fibers; the progenitor of all other connective tissue cell types.
262
Filtration
The movement of a substance across a membane via pressure. In the kidney, filtration refers specifically to the movement of plasma across the capillary walls fo the glomerulus, into the capsule and tubule of the neprhon. Filtration at teh glomerulus is driven by flood pressure.
263
Fimbriae
Fingerlike projection of the uterin (fallopian) tubes that drape over the ovary.
264
First law of Thermodynamics
The law of conservation of energy; the energy of the universe is constant, thus if the energy of a system increases, the energy of its surroundings must decrease, and vice versa.
265
Flagella
A long, whip-like filament that helps in cell motility. Many bacteria are flagellated, and sperm are flagellated.
266
Fluid mosaic model
the current understanding of membrane structure, in which teh membrane iscomposed of a mix o lipids and proteins (a mosaic) that are free to move fluidly among themselves.
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Follicle
A developing oocyte and all of its surrounding (supporting) cells.
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Follicular phase
The first phase of the ovarian cycle, during which a follicle (an oocyte and its surroudning cells) enlarges and matures. This phase is under the control of FSH from the anterior pituitary, and typically lasts from day 1 to day 14 of the menstrual cycle. The follicle secretes estrogen during this time period.
269
Formed elements
The cellular elements of blood; erythrocytes, leukocytes, and platelets.
270
Frameshift mutation
A mutation caused by an insertion or deletion of base pairs in a gene sequence in DNA such that the reading frame of the gene (and thus teh amino acid sequence of the protein) is altered.
271
Frank Starling mechanism
A mechanism by which the stroke volume of the heart is increased by increasing the venous return of the heart (thus stretching the ventricular muscle).
272
FSH
A tropic hormone produced by the anterior pituitary gland that targets the gonads. In females, FSH stimulates the ovaries to develop follicles (oogenesis) and secrete estrogen; in males, FSH stimulates spermatogenesis.
273
Functional synctium
A tissue in which the cytoplasms of the cells are connected by gap junctions, allowing the cells to function as a unit. Cardiac and smooth muscle tissues are examples of functional synctiums.
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G-protein linked receptor
A cell surface receptor associated with an intracellular protein that binds and hydrolyzes GTP. When GTP is bound, the protein is active, and can regulate the activity of adenylyl cyclease; this modifies the intracellular levels of second messenger cAMP. When the GTP is hydrolyzed to GDP, the protein becomes inactive again.
275
Gallbladder
A digestive accessory organ near the liver. The gallbladder stores and concentrates bile produced by the liver, and is stimulated to contrat by cholecystokin (CCK).
276
Gametogenesis
The formation of haploid gametes (sperm or ova) via meiosis.
277
Ganglion
A clump of gray matter (unmyelinated neuron cell bodies) found in the peripheral nervous system.
278
Gap junction
A junction between cells, consisting of a protein channel called a connexon on each of the two cells that connect to form a single channel between teh cytoplasms of both cells. Gap junctions allow small molecules to flow between teh cells, and are important in cell-to-cell communication, for example, in relaying the action potential between cardiac muscle cells, and relaying nutrients between osteocytes.
279
Gap phase
A phase in the cycle between mitosis and S phase (G1) or between S phase and mitosis (G2). During gap phases the cell undergoes normal activity and growth; G1 may include preparation for DNA replication and G2 includes preparation for mitosis. Note that non-dividing cells remain permanently in G1, known as Go for these cells.
280
Gastrin
A hormone released by teh G cells of the stomach in the presence of food. Gastrin promotes muscular activity of the stomach as well as secretion of hydrochloric acid, pepsinogen, and mucus.
281
Gastrulation
the division of the inner cell mass of a blastocyst (developing embryo) into the three primary germ layers. Gastrulation occurs during weeks 2-4 of gestation.
282
Gene
A portion of DNA that codes for some product, usually a protein, including all regulatory sequences. Some genes code for rRNA and tRNA, which are not translated.
283
Gene pool
The sum of all genetic material in a population.
284
Genetic code
The 'language' of a molecular biology that specifies which amino acid corresponds to which three-nucleotide group (codon).
285
Genome
All the genetic information in an organism; all of an organism's chromosomes.
286
Genotype
The combination of alleles of an organism carries. In a homozygous genotype, both alleles are the same, whereas in a heterozygous gentorype the alleles are different.
287
Gibbs free energy
The energy in a system that can be used to drive chemical reactions. If the change in free energy of a reaction (Delta G, the free energy of the products minus the free energy of the energy of the reactants) is negative, the reaction will occur spontaneously.
288
Glomerulus
The ball of capillaries at the beginning of the nephron where blood filtration takes place.
289
Glucagon
A peptide hormone produced and secreted by the alpha cells, of the pancreas. It tartes primarily the liver, stimulating the breakdown of glycogen, thus increasing blood gluocse level.s
290
Glycolipid
A membrane lipid consisting of a glycerol molecule esteried to two fatty acid chains and a sugar molecule.
291
Goblet cells
Unicellular exocrine glands found along the respiratory and digestive tracts taht secrete mucus.
292
Golgi apparatus
A stack of membranes found near the rough ER in eukaryotic cells that is involved in the secretory pathway. The Golgi is involved in protein glycosylation (and other protein modification) and sorting and packagin proteins.
293
Gonadotropin releasing hormone (GnRH
A hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH and LH.
294
Gonadotropins
Anterior pituitary topic hormones FSH (follicle stimulating hormone) and LH (luteinizing homeon) that stimulates the gonads (testes and ovaries) to produce gametes and to secrete sex steroids.
295
Graafian follicle
A large, mature, ovarian follicel with a well-developed antrum and a secondary oocyte. Ovulation of the oocyte occurs from this type of follicle.
296
Gram-negative bacteria
Bacteria that have a thin peptidoglycan cell wall covered by an outer plasma membrane. They stain very lightly (pink) in Gram stain. Gram-negative bacteria are typically more resistant to antibiotics than Gram-positive bacteria.
297
Gram-positive bacteria
Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.
298
Granulosa cells
the majority of the cells surrouding an oocyte in a follicle. Granulosa cells secrete estrogen during the follicular phase of the ovarian cycle (before ovulation).
299
Gray matter
Unmyelinated neuron cell bodies and short unmyelinated axons.
300
Growth hormone
A hormone released by the anterior pituitary that targets all cells in the body. Growth hormone stimulates whole body growth in children and adolescents, adn increases cell turnover rate in adults.
301
Guanine
One of the four aromatic bases found in DNA and RNA. Guanine is a purine; it pairs with cytosine.
302
Gustatory receptors
Chemoreceptors on the tongue that respond to chemicals in a food.
303
Gyrase
A prokaryotic enzyme used to twist teh single circular chromosome of prokaryotes upon itself to form supercois. Supercoiling helps to compact prokaryotic DNa and make it sturdier.
304
H zone
The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction.
305
Hair cells
Sensory receptors found in the inner ear. Cochlear hair cells respond to vibration in the cochlea caused by sound waves and vestibular hair cells respond to changes in position and acceleration (used for balance).
306
Haploid organism
An organism that has only a single copy of its genome in each of its cells. Haploid organisms possess no homolous chromosomes.
307
Hardy-Weinberg law
A law of population genetics that states that the frequencies of alleles in a given gene pool do not change over time. There are five assumptions required for this law to hold true: there must be no mutation, there must be no migration, there must be no random mating between individuals in the population, and the population must be large. A population meeting all of these conditions, in which the allele frequency is not changing, is said to be in Hardy-Weinberg equilibrium.
308
hCG
Human Chorionic Gonadotropin, a hormone secreted by the trophoblast cells of a blasocyst (i.e. developing embryo) that prolongs the life of the corpus luteum, and thus increases the duration and amount of secreted progesterone. This helps to maintain the uterine lining so that menstruation does not occur. The presence of hCG in the blood or urine of a woman is used as a positive indicator of pregnancy.
309
Helicase
An enzyme that unwinds the double helix of DNA and separates the DNA strands in preparation for DNA replication.
310
Hematocrit
The percentage of wholeblood made up of erythrocytes The typical hematocrit value is between 40-45%.
311
Hematopoiesis
The synthesis of blood cells (occurs in the red bone marrow)
312
Hemizygous gene
A gene appearing in a single copy in diploid organisms, e.g. X-linked genes in human males.
313
Hemoglobin
A four-subunit protein found in red blood cells that binds oxygen. Each subunit contains a heme group, a large multi-ring molecule with an iron atom at its center. One hemoglobin molecule can bind four oxygen molecules in a cooperative manner.
314
Hemophilia
An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured.
315
Hemostasis
The stoppage of bleeding; blood clotting.
316
Hepatic portal vein
A vein connecting the capillary bed of the intestines with the capillary bed of the liver. This allows amino acids and gluocse absorbed from the intestines to be delivered first to the liver for processing before being transported throughout the circulatory system.
317
Heterochromatin
DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.
318
Heterotroph
An organism that cannot make its own food, and thus must ingest other organisms.
319
Heterozygous
A genotype in which two different alleles are possessed for a given gene.
320
Hexokinase
The enzymes that catalyzes the phosphorylation of glucose to form glucose-6-phosphate in the first step of glycolysis. This is one of the ain regulatory steps of this pathway. Hexokinase is feedback-inhibited by glucose-6-P.
321
Hfr bacterium
High frequency of recombination bacterium An F+ bacterium that has the fertility factor integrated into its chromosome. When conjugation takes place, it is able to transfer not only the F factor, but also its genomic DNA.
322
Histones
Globular protein that assist in DNA packaging in eukaryotes. Histones form octamers around which DNA is wound to form a nucleosome.
323
hnRNA
Heterogeneous nuclear RNA; the primary transcript made in eukaryotes before splicing.
324
Homeostasis
The maintenance of relatively constant internal conditions (such as temperature, pressure, ion balance, pH, etc.) regardless of external conditions.
325
Homologous chromosomes
A pair of similar chromosomes that have the same genes in the same order, but may have different versions (alleles) of those genes. One of the pair of chromosomes came from Mom in an ovum, and the other came from Dad in a sperm. Humans have 23 pairs of homologous chromosomes.
326
Homologous structures
Physical structures in two different organisms that have structural similarity due to a common ancestor, but may have different functions. Homologous structures arise from divergent evolution.
327
Homozygous
A genotype in which two identical alleles are possessed for a given gene. The allelles can both be dominant (homozygous dominant) or both be recessive (homozygous recessive)
328
Humoral immunity
Specif ic defense of the body by antibodies, secreted into the blood by B-cells.
329
Hydroxyapatite
Hardy crystals consisting of calcium and phosphate that form the bone matrix.
330
Hyperpolarization
The movement of the membrane potential of a cell away from rest potential in a more negative direction.
331
Hypodermis
Aso called a subcutaneous layer, this is a layer of *fat located under the dermis of the skin. The hypodermis helps to insulate the body and protects underlying muscles and other structures.
332
Hypophysis
The pituitary gland.
333
Hypothalamic-pituitary portal system
A set of veins that connect a capillary bed in the hypothalamus (the primary capillary plexus) with a capillary bed in the anterior pituitary gland (the secondary capillary bed). Releasing and inhibiting factors from the hypothalamus travel along the veins to directly affect cells in the anterior pituitary.
334
Hypothalamus
The portion of the diencephalon involved in maintaining body homeostasis. the hypothalamus also controls the release of hormones from the pituitary gland.
335
I band
The regino of the sarcomere made up only of thin filaments. The I band is bisected by a Z line. I bands alternate with A bands to give skeletal and cardiac muscle a striated appearance. I bands get shorter (and may disappear completely) during muscle contraction.
336
Ileocecal valve
The sphincter that separates the final part of the small intestine (the ileum) from the fron part of the large intestine (the cecum). It is typically kept contracted (closed) so that chyme can remain in the small intestine as long as possible. The ileocecal valve is stimulated to relax by the presence of food in the stomach.
337
Ileum
The final section (approximately 55%) of the small intestine.
338
Implantation
The burrowing of a blastocyst (a developing embryo) into the endometrium of the uterus, typically occuring about a week after fertilizaiton.
339
Incomplete dominance
A situation in which a heterozygot displays a blended version of the pheotypes associated with each allele, e.g. pure-breeding white-flowered plants crossed with pure-breeding red-flowered plants produces heterozygous offspring plants with pink flowers.
340
Inducible enzymes
An enzyme whose transcription can be stimulated by an abundance of its substrate (as opposed to repressible enzyme). Usually in catabolism.
341
Induction
The process by which neighboring cells can influence the determination (and subsequent differentiation) of a cell.
342
Inflammation
An irritation of a tissue caused by infection or injury. Inflammation is characterized by four cardinal symptoms; redness (rubor), swelling (tumor), heat (calor), and pain (dolor).
343
Inhibin
A protein hormone secreted by sustenacular cells of the testes that acts to inhibit the release of FSH and LH from the anterior pituitary.
344
Innate immunity
General, non-specific protection to the body, including the skin (barrier), gastric acid, phagocytes, lysozyme, and complement.
345
Inner cell mass
The mass of cells in the blastocyst that ultimately give rise to the embryo and other embryonic structues (the amion, the umbilical vessels, etc.)
346
Inspiration
The movement of air into the respiratory tract. Inspiration is an *active process*, requiring contraction of the diaphragm.
347
Insulin
A peptide hormone produced and secreted by the Beta cells of the pancreas. Insulin targets cells in the body, especially the liver and muscle, and allows them to take glucose out of gthe blood (thus lowering blood glucose levels).
348
Integral membrane protein
A protein embedded in the lipid bilayer of a cell. These are typicallly cell surface receptors, channels, or pumps.
349
Intercalcated discs
The division between neighboring cardiac muscle cells. Intercalcated discs include gap junctions, which allow the cells to function as a unit.
350
Intercostal muscles
Muscles located in between the ribs that play a role in ventilation.
351
Interleukin
A chemical secreted by a T cell (usually the helper Ts) that stimulates activation and proliferation of other immune system cells.
352
Intermediate filaments
Cytoskeletal filaments with a diameter in between that of the microtubule and the microfilament. Intermediate filaments are composed of many different proteins and tend to play structural roles in cells.
353
Interneuron
A neuron found completely within the central nervous system. Interneous typically connect sensory and motor neurons, especially in reflex arcs.
354
Internodal tract
The portion of the cardiac conduction system between the SA node and the AV node.
355
Interphase
All of the cell cycle except for mitosis. Interphase includes G1, S phase, and G2.
356
Interstitial cell
Also called Leydig cells, these are teh cells within testes that produce and secrete testosteron. They are stimulated by luteinizing hormone (LH).
357
Intron
A nucleotide sequence that intervenes between protein-coding sequences. In DNA, these intervening sequences typically contain **regulatory sequences, however, in RNA they are simply spliced out to form the mature (translated) transcript.
358
Ion channel
A protein channel in a cell membrane that is specific for a particular ion, such as Na+ or K+. Ion channels may be constitutively open (leak channels), or regulated (voltage-gated or ligand-gated).
359
IPSP
Inhibitory postsynaptic potential; a slight hyperpolarization of the postysynaptic cell, moving the membrane potential of that cell further from threshold.
360
Iris
A pigmented membrane found just in from the lens of the eye. In the center of iris is the pupil, a hole through which light enters the eyeball. The iris regulates the diameter of the pupil in response to the brightness of light.
361
Islets of Langerhans
Also called simply, "islet cells" these are the endocrine cells of the pancreas. Different cell types wihtin the inslets secrete insulin, glucagon, and somatostatin
362
Jejunum
The middle (approximtely 40%) of the small intestine.
363
Juxtaglomerular apparatus (JGA)
A contact point between the afferent arteriole of the glomerulus and the distal convoluted tubule of the nephron. It is involved in regulating blood pressure.
364
Juxtaglomerular cells.
The cells of the afferent artery at the juxtaglomerular apparatus. They are baroreceptors that secrete renin upon sensing a decrease in blood pressure.
365
Keratin
A protein-based substance secreted by cells of the epiderms as they migrate outward. The keratin makes the cells tougher (better able to withstand abrasion) and helps make the skin waterproof.
366
Kinase
An enzyme that phosphorylates something else. Kinases are frequently used in regulatory pathways, phosphorylating other enzymes.
367
Krebs cycle
The third stage of cellular respiration, in which acetyl-CoA is combined with oxaloacetate to form citric acid. The citric acid is then decarboxylated twice and isomerized to recreate oxaloacetate. In the process, 3 molecules of NADH, 1 molecule of FADH2, and 1 molecule of GTP are formed (per acetyl-CoA)
368
Labia
The folds of skin that enclose the vaginal and urethral openings of females.
369
Labor contractions
Strong contractions of the uterus (stimulated by oxytoncin) that force a baby out of the mother's baby during childbirth. Labor contractions are part of a positive feedback cycle, during which the baby's head stretches the cervix, which stimulates stretch receptors that activate the hypothalamus, which stimulates the posterior pituitary to release oxytocin, which stimulates strong uterine contractions (labor contractions) that cause the baby's head to stretch the cervix. The cycle is broken once the baby is delivered.
370
Lacteals
Specialized lymphatic capillaries in the intestines that take up lipids as well as lymph.
371
Lactic acid
Produced in muscle cells from the reduction of pyruvate (under anaerobic conditions) to regenerate NAD+ so that glycolysis can continue. A rise in lactic acid usually accompanies an increase in physical activity.
372
Lacunae
Small cavities in the bone or cartilage that hold individual bones or cartilage cells.
373
Lag phase
A short period of time **prior to exponential growth of a bacterial population during which no, or very limited, cell division occurs.
374
Lagging strand
The newly forming daughter strand of DNA that is replicated in a discontinuous fashion, via Okazaki fragments that will ultimately be ligated together; the daugther strand that is replicated in the opposite direction that parallel DNA is unwinding
375
Large intestine
The final phase of the digestive tract, also called the colon. The primary funcion of the large intestine is to reabsorb water and to store the feces.
376
Larynx
A rigid structure at the top of the trachea (so it is part of trachea, I assume) made completely out of cartilage. The larynx has three main functions: (1) its rigidness ensures that the trachea is held open (provides an open airway). (2) the epiglottis folds down to seal the trachea during swallowing, thus directing food the espohagus, and (3) this is where the vocal cords are found (voice production).
377
Law of Independent Assortment
Mendel's seond law. States that genes found on different chromosomes, or genes found very far apart on the same chromosome (i.e., unlinked genes) sort independently of one another during gamete formation (meiosis).
378
Law of Segregation
Mendels' first law. The Law of Segregation states that the two alleles of a given gene will be separate from one another during gamete formation (meiosis).
379
Lawn
A dense grwoth of bacteria that covers the surface of a petri dish.
380
Leading strand
The newly forming daughter strand of DNA that is replicated in a continuous fasion; the daughter strand that is replicated in thes aem direction that parental DNA is unwinding.
381
Leak channel
An ion channel that is constitutively open, allowing the movement of teh ion across the plasma membrane according to its concentration gradient.
382
Length-tension relationship
The relationship of muscle length to its ability to generate strong contractions. Maximum tension (contraction strength) is achieved at sarcomere lengths between 2.0 and 2.2 microns. Tension decreases outside of this range <-- remember.
383
Leukocyte
A type of white blood cell; leukocytes are either B or T cells and are involved in disease defense.
384
Ligament
A strong band of connective tissue that connets bones to one another.
385
Ligand
The specific molecule that binds to a receptor.
386
Ligand-gated ion channel
An ion channel that is opened or closed based on the binding of a specific ligand to teh channel. Once opened, the channel allows the ion to cross the plasma membrane according to its concentration gradient. An examples is the acetylcholine receptor at the neuromuscular junction, which, when Ach binds, opens a cation channel in the muscle cell membrane.
387
Ligase
An enzyme that connects two fragments of DNA to make a single fragment; also called DNA ligase. This enzyme is usedd during DNA replication and is also used in recombinant DNA research.
388
Linkage
The failure of two separate genes to boey the Law of Independent Assortment, as might occur if the genes were found close together on the same chromosome.
389
Linker DNA
The string between beads of DNA on histones. They are also wrapped around a single histone, called linker histone - may not really have to know..
390
Lipid
A hydrophobic molecule, usually fomred from long hydrocarbon chains. The most common forms in which lipids are found in the body are as triglycerides (energy storage), phospholipids (cell membranes), and cholestero (cell membranes and steroid synthesis).
391
Lipoprotein
Large conglomerations of proteins, fats, and cholesterol that transport lipids in the bloodstream. (chylomicrons are a type of lipoprotein).
392
Liver
The largest organ in the abdominal cavity. The liver has many roles, including procesing of carbohydrates and fats, synthesis of urea, production of blood proteins, production of bile, recycling heme, and storage of vitamins.
393
Local autoregulation
The ability of tissues to regulate their own blood flow in the absence of neural stiulation. THis is generally accomplished via metabolic wastes (such as CO2) that act as vasodilators.
394
Log phase
The period of exponential growth of bacterial population.
395
Long bone
The most common class of bone in the body, long bones have a well-defined shaft (the diaphysis) and two well-defined ends (the epiphyses).
396
Longitudinal muscle
The outer layer of smooth muscle in the wall of the digestive tract. When the longitudinal muscle contracts the tube shortens.
397
Loop of Henle
The loop of the nephron that dips downward into the renal medulla. The loop of Henle sets up a concentration gradient in the kidney such that from the cortex to the renal pelvis osmolarity increases. The descending limb of the loop of Henle is permeable to water, but not to sodium whereas the ascending limb is permeable to sodium, but not to water (and in fact, actively transports sodium out of the filtrate).
398
Loose connective tissue
Connective tissue that lacks great amount of collagen or elastic fibers (hence, loose), e.g., adipose tissue and areolar (general connective) tissue.
399
Lower esophageal sphincter
Formerly called the cardiac sphincter, this sphincter marks the entrance to the stomach. Its function is to prevent reflux of acid stomach contents into the esophagus; note that it does ***not regulate entry into the stomach*.
400
Lumen
The inside of the a hollow organ (e.g., the somach, intestines, bladder, etc.) or a tube (e.g., blood vessels, ureters, etc.)
401
Luteal phase
The third phase of the ovarian cycle, during which a corpus luteum is formed from the remnants of the follicle that has ovulated its oocyte. The corpus luteum secretes progestrone and estrogen during this time period, which typically lasts from day 15 to day 28 of the menstrual cycle. Formation of the corpul luteum is triggered by the same LH surge that triggers ovulation, however in the absence of LH (levels quickly decline after the surge) the corpus luteum begins to degenerate.
402
Luteinizing Hormone (LH)
A tropic hormone produced by the anterior pituitary gland that targets the gonads. In females LH triggers ovulation and the development of a corpus luteum during the menstrual cycle; in males, LH stimulates the production and release of testosteron.
403
Lymph node
A concentrated region of white blood cells found along the vessels of the lympatic system.
404
Lymphatic system
A set of vessels in the body that runs alongside the vessels of the circulatory system. It is a one-way system, with lymphatic capillaries beginning at the tissues and ultimately emptying into the large veins near the heart. It serves to return excess tissue fluid (lymph) to the circulatory system, and filters the fluid through millions of white blood cells on its way back to the heart.
405
Lymphocyte
The second most common of the five classes of leukocytes. Lymphocytes are involved in specific immunity and include two cell types, B-cells and T cells. B-cells produce and secrete antibodies and T-cells are invovled in cellular immunity.
406
Lymphokine
A chemical secreted by a T cell (usually the helper Ts) that stimulates activation and proliferation of other immune system cells.
407
Lysogenic cycle
A viral life cycle in which the viral genome is incorporated into the host genome where it can remain dormant for an unspecified period of time. Upon activation, the viral genome is excised from the host genome and typically enters the lytic cycle.
408
Lysosome
A eukaryotic organelle filled with digestive enzymes (acid hydrolases) that is involved in digestion of macromolecules such as worng organelles or material ingested by phagocytosis.
409
Lysozyme
An enzyme that lyses bacterial cell walls. Lysozyme is produced in the end stages of the lytic cycle so that new viral particles can escape their hosst; it is also found in human tears and human saliva.
410
Lytic cycle
A viral life cycle in which the host is turned into a "virus factory" and ultimately lysed to release the new viral particles.
411
Macrophage
A large, non-sepcific, phagocytic cell of the immune syste. Macrophages frequently leave the bloodstream to crawl around in the tissues and perform 'clean up' duties, such as ingesting dead cells or cellular debris at an injury site, or pathogens.
412
Macula densa
The cells of the distal tubule at the juxtaglomerular apparatus. They are receptors that monitor filtrate osmolarity as a means of regulatin filtration rate. If a drop is osmolarity is sensed, the macula densa dilates the afferent arteriole (to increase the blood pressure in the glomerulus and thus increase filtration) and stimulates the juxtaglomerular cells to secrete renin (to raise systemic blood pressure).
413
Maternal inheritance
Genes that are inherited only from the mother, such as mitochondrial genes (all organelles come only from the ovum).
414
Matrix
The interior of a mitochondrion (the region bounded by the inner membrane)., The matrix is the site of action of pyruvate dehydroganse complex and the Krebs cycle.
415
Mechanoreceptors
A sensory receptor that responds to mechanical disturbances, such as shape changes (being squashed, bent, pulled, etc.). Mechanoreceptors include touch receptors in the skin, hair cells, in the ear, muscle spindles, and others.
416
Medium
The environment in which or upon which bacteria grow. It typically contains a sugar source and any other nutrients that bacteria may require. 'Minimal medium' contain nothing but glucose.
417
Medulla
The inner region of an organ, e.g., the renal medulla, the ovarian medulla, and the adrenal medulla, etc.
418
Medulla oblongata
The portion of the hindbrain that controls respiratory and blood pressure, and specialized digestive and respiratory functions such as vomiting, sneezing, and coughing.
419
Meiosis
A type of cell division (in diploid cells) that reduces the number of chromosomes by half. Meiosis usualy produces haploid gametes in organisms that undergo sexual reproduction. It consists of a single interphase (G1, S, and G2) followed by two sets of chromosomal divisions, meiosis I and meiosis II. Meiosis I and II can both be subdivided into four phases similar to those in mitosis.
420
Melanin
A pigment produced by melanocytes in teh bottom cell layer of the epidermis. Melanin production is increased on sun exposure and helps prevent cllular damage due to UV radiation.
421
Memory cell
A cell produced when a B cell is activated by antigen. Memory cells do not actively fight the current infection, but patrol the body in case of future infection with the same antigen. If the antigen should appear again the future, memory cells are like 'preactivated' B cells, and can initiate a much faster immune response (the secondary immune response).
422
Meninges
The protective, connective tissue wrapping of the central nervous system (the dura mater, arachnoid mater, and pia mater).
423
Menopause
The perio dof tim ein a woman's life when ovulation and menstruation cease. Menopause typically begins in the late 40s.
424
Menstruation
The first phase of the uterine (endometrial) cycle, during which the endometrium from the previous cycle is shed off. Estrogen and progesterone levels are low during this time period. Menstruation typically lasts from day 1 to day 5 of the cycle.
425
Mesoderm
One of the three primary (embryonic) germ layers formed during gastrulation. Mesoderm ultimately forms 'middle' structures such as bones, muscles, blood vessels, heart, kindeys, etc.
426
Metaphase
The secon phase of mitosis. During metaphase chromosomes align at the center of the ell (the metaphase plate).
427
Metaphase I
The second phase of meiosis I. During metaphase I the paired homologous chromsomes (tetrads) align at the center of the cell (the metaphase plate).
428
Metaphase II
The second phase of meiosis II. Metaphase II is identical to mitotic metaphase, except that the number of chromosomes was reduced by half during meiosis I.
429
MHC
Major Histocompatability complex, a set of proteins found on the plasma membranes of cells that help display antigen to T cells. MHC I is found on all cells and displays bits of proteins from within the cell; this allows T cells to monitor cell contents and if abnormal peptides are displayed on the surface, the cell is destroyed by killer T cells. MHC II is found only on macrophages and B cells. This class of MHC allows these cells (known as antigen presenting cells) to display bitts of "eaten" (phagocytosed or internalized) proteins on their surface, allowing the activation of helper Ts --> thus further activating immune response.
430
Microfilament
The cytoskeleton filaments with the smallest diameter. Microfilaments are composed of the contractile protein actin. They are dynamic filaments, constantly beig made and broken down as needed, and are responsible for events such as pseudopod formation and cytokenesis during mitosis.
431
Microtubule
The largest of the cytoplasmic filaments. Microtubules are composed of two types of protein, alpha tubulin and beta tubulin. They are dynamic fibers, constantly being built up and broken down, according to cellular needs. Microtubules form the mitotic spindle during cell division, form the base of cilia and flagella, and are used for intracellular structure and transport.
432
Microvilli
Microscopic outward folds of the cells lining the small intestine; microvilli serve to increase the surface area of the small intestine for absorption.
433
Midbrain
The portion of the brain responsible for visual and auditory startle reflexes.
434
Milk letdown
The release of milk from the mammary glands via contraction of ducts within the glands. Contraction is stimulated by oxytocin, which is released from the posterior pituitary when the baby begins nursing.
435
Missense mutation
A point mutation in which a codon that specifies an amino acid is mutated into a codon that specifies a different amino acid.
436
Mitochondrion
An organelle surrounded by a double=membrane (two lipid bilayers) where ATP production takes place. The interior (matrix) is where PDC and the Krebs cycle occur, and the inner membrane contains the enzymes of the electron trasport chain and ATP synthase.
437
Mitosis
The phase of the cell cycle during which the replicated genome is divided. Mitosis has four phases (prophase, metaphase, anaphase, telophase) and includes cytokinesis (the physical splitting of the cell into two new cells).
438
Monocistronic mRNA
mRNA that codes forsingle type of protein, such as is found in eukaryotic cells.
439
Monosaccharide
The monomer of a carbohydrate. Monosaccharides have the general chemical formula CnH2nOn, and common monosaccharides include glucose, fructose, galactose, and ribose.
440
Morula
A solid clump of cells resulting from cleavage in the early embryo. Because there is very little growth of these cells during cleavage, the morula is ony about as large as the original zygote.
441
Motor end plate
The portion of the cell membrane at the neuromusclar junction; essentially the postsynaptic membrane at the synapse.
442
Motor unit
A motor neuron and all the all the skeletal muscle cells it innervates. Large motor units are typically found in large muscles (e.g., the thighs and buttocks) and produce fross movements. Small motor untis are found in smaller muscles (e.g. the rectus muscles that controle movements of the eyeball, the fingers) and produce more precise movements.
443
Motor unit recruitment
A mechanism for increasing tension (contractile length) in a muscle by activating more motor units.
444
mRNA
Messenger RNA; the type of RNa that is read by a ribosome to synthesize protein.
445
Mucocilliary escalator
The layer of ciliated, mucus-covered cells in the respiratory tract.The cilia continually beat, sweeping contaminated mucus upward toward the pharynx.
446
Mucosa
The layer of epithelial tissue that lines body cavities in contact with the outside environment (respiratory, digestive, urinary, and reproductive tracts).
447
Mullerian ducts
Earlier embryonic ducts that can develop into femal internal genitalia in the absence of testosteron.
448
Mullerian inhibiting factor (MIF)
A substance secreted by embryonic testes that causes the regression of the Mullerian ducts.
449
Multipolar neuron
A neuron with a single axon and multiple dendrites; the most common type of neuron in the nervous system.
450
Mutualism
A form of symbiosis in which both organisms involved benefit from the association.
451
Myelin
An insulating layer of membranes wrapped around the axons of almost all neurons in the body. Myelin is essentially the plasma membranes of specialized cells; Schwann cells in the peripheral nervous system, and oligodendrocytes in the central nervous system.
452
Myofiber
A skeletal muscle cell, also known as a muscle fiber. Skeletal muscle cells are formed from the fusion of many smaller cells (during development) consequently they are very long and are multinucleate.
453
Myofibril
A string of sarcomeres with a skeletal muscle cell (hence smaller than myofiber). Each muscle cell contains hundreds of myofibirils.
454
Myoglobin
A globular protein found in muscle tissue that has the ability to bind oxygen. Myoglobin helps to store oxygen in the muscle for use in aerobic respiration (it does not move, just stays there). Muscles that participate in endurance activities (including cardiac muscle) have abundant supplies of myoglobin.
455
Myometrium
The muscuar layer of the uterus. The myometrium is made of smooth muscles that retains its ability to divide in order to accomodate the massive size increases that occur during pregnancy. The myometrium is stimulated to contract during labor by the hormone oxytocin.
456
Myosin
One of the contractie proteins in muscle tissue. In skeletal and cardiac muscles, myosin forms the thick filaments. Myosin has intrinsic ATPase activity and can exist in two conformation, either high energy or low energy.
457
Myosin light-chain kinase (MLCK)
A kinase in smooth muscle cells activated by calmodulin the presence of Ca2+. As its name implies, this kinase phosphorylates myosin, activating it so that muscle contraction can occur.
458
Na+/K+ ATPase
A protein found in the plasma membrane of all cells in the body that uses the energy of an ATP (hydrolyzes ATP) to move three Na+ ions out of the cell and two K+ ions into the cell, thus establishing concentrations gradients for these ions across the cell membrane.
459
NADH
The reduced form of NAD+ (nicotinamide adenine dinucleotide). This is the most common electron carrier in cellular respiration.
460
Natural selection
The mechanism described by Charles Darwin that drives evolution. Through mutation, some organisms possess genes that make them better adapted to their environment. These organisms survive and reproduce more than those that do not possess the beneficial genes, thus these genes are passed on to offspring, making the offspring better adapted. Over time, these genes (and the organisms that possess them) become more abundant, and the less beneficial genes (and the organisms that possess them) become less abundant.
461
Nephron
The function unit of the kidney. Each kidney has about a million nehprons; this is where blood filtration and subsequent modification of the filtrate occurs. The nephron empties into collecting ducts, which empty into the ureter.
462
Neuralation
The formatino of the nervous system during weeks 5-8 of gestation. Neuralation begins when a section of the ectoderm invaginates and pinches off to form the neural groove, which ultimately forms the neural tube, from which the brain and spinal cord develop.
463
Neuromuscular junction
The synapse between a motor neuron and a muscle cell. At the NMJ, the muscle cel lmembrane is invaginated and the axon terminus is elongated so that a greater area of membrane can be depolarized at one time.
464
Neuron
The basic functional and structural unit of the nervous system. The neuron is a highly specialized cell, designed to transmit action potentials.
465
Neurotransmitter
A chemical released by the axon of a neuron in response to an action potential that binds to receptors on a postsynaptic cell and causes that cell to either depolarize slightlly (EPSP) or hyperpolarize slightly (IPSP). Examples are acetylcholine, norepinephrine, GABA, dopamine, and others.
466
Nociceptors
Pain receptors. Nociceptors are found everywhere in the body except for the brain.
467
Nodes of Ranvier
Gaps in the myelin sheath of the axons of peripheral neruons. Action potentials can 'hump' from node to node, thus increasing the speed of conduction (saltatory conduction).
468
Noncompetitive inhibitor
An enzyme inhibitor that binds at a site other than the active sit of an enzyme (binds at an allosteric site). THis changes the three-dimensional shape of the enzyme such that it can no longer catalyze the reaction
469
Nondisjunction
The failure of homologous chromosomes or sister chromatids to separate properly during cell division. This could ocur during *anaphase I of meiosis (homologous chromosomes) [--> leaving 2 gametes w/ 2 copies and 2 gametes w/ no copies of chromosome], or during *anaphase II of meiosis or *anaphase of mitosis (sister chromatids).
470
Nonsense mutation
A point mutation in which a condon that specifies an amino acid is mutated into a stop (nonsense) codon.
471
Norepinephrine
The neurotransmitter used by the sympathetic division of the ANS at the postganglionic (organ-level ) synapse.
472
Nuclear envelope
The membrane surrounding the DNA in eukaryotic cells made of two lipid bilayers.
473
Nuclear localization sequence
A sequence of amino acids (usually basic) that directs a protein to the nuclear envelope, where it is imported by a specific transport mechanism.
474
Nuclear pore
A protein channel in the nuclear envelope that llows the free passage of molecules smaller than 60 kD.
475
Nucleolus
A region within the nucleus where rRNA is transribed and ribosomes are partially assembled.
476
Nucleoside
A structure composed of a ribose molecule linked to one of the aromatic bases. In a deoxynucleoside, the ribose is replaced with deoxyribose.
477
Nucleosome
A structure composed of two coils of DNA wrapped around an octet of histone proteins. The nucleosome is the primary form of packagin of eukaryotic DNA.
478
Nucleotide
A nucleoside with one or more phosphate gropus attached. Nucleoside triphosphates (NTPs) are the building blocks of RNA and are also used as energy molecules, especially ATP. Deoxynucleoside triphosphates (dNTPs) are the building blocks of DNA; in these molecules, the ribose is replaced with deoxyribose.
479
Nucleus
An organelle bounded by a double membrane (double lipid bilayer) called the nuclear envelope. The nucleus contains the genome and is the site of replication and transcription.
480
Obligate aerobe
An organism that requires oxygen to survive (aerobic metabolism only).
481
Obligate anaerobe
An organism that can only survive in the absence of oxygen (anaerobic metabolism); oxygen is toxic to obligate anaerobes.
482
Okazaki fragments
Small fragments of DNa produced on the lagging strand during DNa replication, joined later by DNA ligase to form a complete strand.
483
Olfactory receptors
Chemoreceptors in the upper nasal cavity that respond to odo chemicals.
484
Oncotic pressure
The osmotic pressure in the blood vessels due only to plasma proteins (primarily albumin) --> causes water to rush back into capillaries at end.
485
Oogonium
A *precursor* cell that undergoes mitosis during fetal development to produce more oogonium. These cells are then activated to produce primary oocytes, which remain dormant until stimulated to undergo meiosis I during some future menstrual cycle.
486
Operator
A specific DNA nucleotide sequence where transcriptional regulatory proteins can bind.
487
Operon
A nucleotide sequence on DNA that contians three elemtns: a coding sequence for one or more enzymes, *a coding sequence for a regulatory protein, and upstream regulatory sequences where the regulatory proteins can bind. An example is the lac operon found in prokaryotes.
488
Optic disk
The 'blind spot' of the eye, this is where the axons of the ganglion cells exist the retinal to form the optic nerve. There are no photoreceptors in the optic disk.
489
Optic nerve
The nerve extending from the back of teh eyeball to teh brain that carries visual information. The ptic nerve is made up of the axons of the ganglion cells of the retina.
490
Organ of Corti
The structure in the cochlea of the inner ear made up of the basilar membrane, the auditory hair cells, and the tectorial membrane. The Organ of Corti is the site where auditory sensation is detected and transduced to action potentials.
491
Organogenesis
The stage of human development during which the organs are formed. Organogenesis begins after gastrulation and is completed by the eight week of gestation.
492
Orgasm
A function of the reproductive system controlled by the sympathetic nervous system. In males, organs includes emission and ejaculation; in females it is mainly a series of rhythmic contraction of the pelvic floor muscles and the uterus.
493
Origin of replication
The specific location on a DNa strand where replication begins.. Prokaryotes typically have a single origin of replication, while eukaryotes have several per chromosome.
494
Osmosis
The movement of water (the solvent) from its region of high concentration to its region of low concentration. NOte that the water concnetration gradient is opposite to the solute concentration gradient, since where solutes are concentrated, water is scarce.
495
Osmotic pressure
The force required to resist the movement of water by osmosis. Osmotic pressure is essentialy a measure of the concentration of a solution. A solution that is hyighly concnetrated has a strong tendency to draw water into itself, so the pressure required to resist that movement would be high. Thus, highly concentrated solutions are said to have high osmotic pressures.
496
Ossicles
The three small bones found in the middle ear (the malleus, the incus, and the stapes) that help to amplify the vibrations from sound waves. The malleus is atached to the tympanic membrane and the stapes is attached to the oval window of the cochlea.
497
Osteoblast
A cell that produces bone.
498
Osteoclast
A phagocytic-like bone cell that breaks down bone matrix to release calcium and phosphate into the bloodstream.
499
Osteocyte
A mature, dormant osteoblast.
500
Osteon
The unit of combact bone, also called a Haversian system. Osteons are essentially long cylinders of bone; the hollow center is called the central canal, and is where blood vessels, nervs, and lymphatic vessels are found. Compact bone is laid down around the central canal in rings (lamellae).
