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Flashcards in Biology Deck (500):
1

5' cap

a methylated guanine nucleotide added to the 5' end of eukaryotic mRNA. The cap is necessary to initiate translation of mRNA

2

A band

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.

3

Absolute refractory period

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)

4

Accessory glands

The three glands in the male reproductive system that reproduce semen: the seminal vesicles, the prostate, and the

5

Accessory organs

(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.

6

Acetylcholine (Ach)

The neurotransmitter used throughout the parasympathetic nervous system as well as the neuromuscular junction.

7

Acetylcholinesterase (AChE)

The enzyme that breaks down acetylcholine in the synaptic cleft.

8

Acetyl-CoA

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

Acid hydrolases

Enzymes that degrade various macromolecules and that require an acidic pH to function properly. Acid hydrolases are found within the lysosomes of cells.

10

Acinar cells

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.

11

Acrosome

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

12

Actin

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.

13

Action potential

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.

14

Activation energy (Ea)

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.

15

Active site

The 3D site of an enzyme where substrates (reactants) bind and a chemical reaction is facilitated.

16

Active transport

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.

17

Adenine

One of the four aromatic bases found in DNA and RNA; also a component of ATP, NADH, and FADH2. Adenine is apurine; it pairs with thymine (in DNA) and with uracil (in RNA)

18

Adenohypophis

anterior pituitary gland

19

Adipocyte

fat cell

20

Adrenal medulla

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.

21

Adrenergic tone

A constant input to the arteries that keeps them somewhat constricted to maintain a basal level of blood pressure.

22

Adrenocoricotropic hormone (ACTH)

A trop hormone produced by the anterior pituitary gand that targets the adrenal cortex, stimulating it to relase corisol and aldosterone.

23

Afferent arteriole

The small artery that carries blood toward the capillaries of the glomerulus.

24

Afferent neuron

A neuron that arries information (action potentials) to the central nervous system; a sensory neuron.

25

Albumin

A blood protein produced by the liver. Albumin helps to mantain blood osmotic pressure (oncotic pressure)

26

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).

27

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.

28

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)

29

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.

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

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.

32

Amino acid acceptor site

The 3' end of a tRNA molecule that binds an amino acid. The nucleotide sequence at this end is CCA

33

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

34

Aminion

A sac filled with fluid (aminotic fluid) that surroudns and protects a developing embryo.

35

Amphipathic

The characteristics of amolecule that has both polar (hydrophilic) and non-polar hydrophobic) regions, e.g. phospholipids, bile, etc.

36

Amylase

An enzyme that digests starch into disaccharides. Amylase is secreted by salivary glands and by the pancreas.

37

Anabolism

The process of bulidng complex structures out of simpler precursors, e.g. synthesizing protiens from amino acids.

38

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.

39

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).

40

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.

41

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.

42

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.

43

Androgens

Mal sex hormones. Testosteron is the primary androgen.

44

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.

45

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.

46

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.

47

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.

48

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.

49

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.

50

Antigen (Ag)

A molecule (usually a protein) capable of initiating an immune repsonse (antibody production).

51

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"

52

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

53

Antiporter

A carrier protein that transports two molecules acrss the plasma membrane in opposite directions.

54

Aorta

The largest artery in teh body; the aorta carries oxygenated blood away from the left ventricle of the heart.

55

Appendix

A mass of lymphatic tissue at the befenning of the large intestine that helps trap ingested pathogens.

56

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

57

Arousal

A function in the reproductive system, controlled by the parasympathetic nervous system, that includes erection (via dilation of erectile arteries) and lubrication.

58

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.

59

A site

Amino-acyl tRNA site; the site on a ribosome where a new amino acid is added to a growing peptide.

60

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

61

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.

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 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).

64

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.

65

Attachment

The first step in viral infection. Attachemen of a virus to its host is very specific and is also known as adsorption.

66

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.

67

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.

68

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.

69

Autosome

A chromosome that does not determine gender (is not a sex chromosome). Humans have two sex chromsomes and 22 autosomes.

70

Autotroph

An organism that makes its own, typically using CO2 as a carbon source.

71

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)

72

Avascular

Lacking a blood supply; cartialge is an example of this

73

Axon

A long projection off the cell body of a neruon down which an action potential can be propagated.

74

Bacilus

A bacterium having a rod-like shaped (plural = bacilli).

75

Bacteriophage

A virus that infects a bacterium.

76

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.

77

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.

78

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.

79

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.

80

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.

81

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.

82

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.

83

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.

84

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.

85

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.

86

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.

87

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.

88

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.

89

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.

90

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.

91

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).

92

Calcitriol

A hormone produced from vitamin D that acts in essentially the same manner as parathyroid hormone.

93

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.

94

Canaliculus

Very small tube or channel, such as is found between lacunae (connecting them together) in compact bone.

95

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.

96

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.

97

Capsid

The outer protein coat of a virus (the whole coat)

98

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).

99

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).

100

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.

101

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.

102

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**.

103

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'.

104

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.

105

Catabolism

The process of breaking down large molecules into smaller precursors, e.g. digesion of starch into glucose.

106

Catalase

The primary enzyme in peroxisomes; catalse catalyzes the hydrolysis of hydrogen peroxide (H2O2) into water and oxygen.

107

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.

108

cDNA

Complementary DNA. DNA produced synthetically by reverse trascribing mRNA. Because of eukaryotic mRNA splicing, cDNA contains no inrons.

109

Cecum

The first part of the large intestine.

110

Cell surface receptor

An integral membrane proteint hat binds extracellular signaling molecules, suchas hormones and peptides.

111

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.

112

Central chemoreceptors

Receptors in the central nervous system that monitor the pH of cerebrospinal luid to help regulate ventilation rate.

113

Central Nervous System

The subdivision of the nervous system consisting of the brain and spinal cord.

114

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.

115

Centromere

A structure near the middle of eukaryotic chromosomes to which the fibers of the mitotic spindle attach during cell division.

116

Cerebellum

The region of teh brain that coordinates and smooth skeletal muscle activity.

117

Cerebral cortex

A thin (4 mm) layer of gray matter on the surface of 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.

118

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.

119

Ceruminous gland

A gland that secretes a waxy product, found in the external ear canal.

120

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.

121

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'.

122

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.

123

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).

124

Chemotaxis

Movement that is directed by chemical gradients, such as nutrients or toxins. (seen in some bacteria)

125

Chemotroph

An organism that relies on a chemical source of energy (such as ATP) instead of light (which phototrophs).

126

Chief cells

Pepsinogen-secreting cells foudn at teh bottom of the gastric glands

127

Chitin

A poysaccharide found in the cell walls of fungi and in the exoskeletons of insects.

128

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.

129

Cholesterol

A large, ring shaped lipid found in cell membranes. Cholesterol is the precursor for steroid hormones, and is used to manufacture bile salts.

130

Chondrocyte

A mature, cartilage cell.

131

Chorion

The portion of the placenta derived from the zygote.

132

Choroid

The darkly pigmented middle layer of the eyeball, found between teh sclera (outer layer) and the retina (inner layer).

133

Chromosome

A single piece of double-stranded DNA; part of the genome of an organism. Prokaryotes have circular chromosomes and eukaryotes have linear chromosomes.

134

Chylomicron

A type of lipoprotein; the form in which absorbed fats from the intestines are transported to the circulatory system.

135

Chyme

Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.

136

Chymotrypsin

One of the main pancreatic proteases; it is activated (from chymotrypsinogen) by trypsin.

137

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.

138

Ciliary muscles

Muscles that help focus light on teh retin by controlling the curvature of the lens of the eye.

139

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).

140

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).

141

Cleavage

The rapid mitotic division of a zygot that being within 24-36 hours after fertilization

142

Coccus

A bacteria having a round shape (plural = cocci)

143

Cochlea

The curled structure in the inner ear that contains the membranes and hair cells that transduce sound waves into action potentials.

144

Codominance

A situation in which a heterozygote displays the phenotype associated with each of the alleles, e.g., human blood type AB.

145

Codon

A group of three nucleotides taht is specific for a particular amino acid, or that specifies 'stop translating'

146

Coenzyme

An **organic molecuel taht associates non-covalently with an enzyme, and that is required for the proper functioning of the enzyme.

147

Cofactor

An **inorganic molecule that associates non-covalently with an enzyme and that is required for the proper functioning of the enzyme

148

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.

149

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.

150

Common bile duct

The duct that carries bile from the gallbladder and liver to the small intestine (duodenum).

151

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.

152

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.

153

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.

154

Cones

Photoreceptors in the retina of the eye that responds to bright light and provide color vision.

155

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.

156

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.

157

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.

158

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.

159

Cornea

The clear portion of the tough outer layer of teh eye ball, found over the iris and pupil

160

Corona radiata

The layer of granulosa cells taht surround an oocyte after is has been ovulated.

161

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.

162

Corpus callosum

The largest bundle of white matter (axons) connecting th two cerebral hemispheres.

163

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.

164

Cortex

The outer layer of an organ, e.g. the renal cortex, the ovarian cortex, the adrenal cortex, etc.

165

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.

166

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.

167

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.

168

Cristae

The folds of the inner membrane of a mitochondrion

169

Cross bridge

The connection of a mosin head group to an actin filament during muscle contraction (the sliding filament theory).

170

Crossing over

The exchange of DNA between paired homologus chromosomes (tetrads) during *prophase I* of meiosis.

171

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.

173

Cytosine

One of the four aromatic bases found in DNA and RNA. Cytosine is a pyrimidine; it pairs with guanine.

174

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!

175

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.)

176

Depolarization

The movement of teh membrane potential of a cell away from rest potential in a more positive direction.

177

Dermis

A layer of connective tissue underneath the epidermis of the skin. The dermis contains blood vessels, lymphatic vessels, nerves, sensory receptors, and glands.

178

Desmosome

A general cell junction, used primarily for adhesion.

179

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.

180

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.

181

Diaphysis

The shaft of a long bone. The diaphysis is hollow and is made entirely from compact bone.

182

Diastole

The perio of time during which the ventricles of the heart are relaxed.

183

Diastolic pressure

The pressure measured in the arteries while the ventricles are relaxed (during diastole).

184

Diencephalon

The portion of theforebrain that includes the thalamus and hypothalamus.

185

Differentiation

The specialization of cell types, especially during the embryonic and fetal development.

186

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).

187

Diploid organism

An organism that has two copies of its genome it each cell. The paired genomes are said to be homologous.

188

Disaccharide

A molecule composed of two monosaccharides. Common disaccharides include maltose, sucrose, and lactose.

189

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.

190

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.

191

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.

192

Dominant

The allele in a heterozygous genotype that is expressed; the phenotype resulting from either a heterozygous genotype or a homozygous dominant genotype.

193

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).

194

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.'

195

Duodenum

The first (approximately 5%) of the small intestinte.

196

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.

197

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.

198

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).

199

Effector organ

The organ that carries out teh command sent along a particular motor neuron

200

Efferent arteriole

The small artery that carries blood away from the capillaries of the glomerulus.

201

Efferent neuron

A neuron that carries information (action potentials) away from the central nervous system; a motor neuron.

202

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.

203

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.

204

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.

205

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.

206

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.

207

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.

208

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.

209

Endocrine gland

A ductless gland that secretes a hormone into the blood

210

Endocrine system

A systme of ductless glands taht secrete chemical messengers (into) the blood - has to be into the blood.

211

Endocytosis

The uptake of material into a cell, usually by invagination. See also 'phagocytosis', pinocytosis, and receptor-mediated endocytosis..

212

Endoderm

One of the three primary (embryonic) germ layers formed during gastrulation. Endoderm ultimately forms internal structures, such as the inner lining of the GI tract and glandular organs.

213

Endometrial cycle

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.

214

Endometrium

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.

215

Endospore

A bacterial structure formed in unfavorable growth conditions. Endospores have very rough outer shells made of peptidoglycan and can survive harsh conditions. The bacterium inside the endospore is essentially dormant and can become active (called germination) when conditions again become favorable.

216

Endosymbitoic theory

the theory that mitochondria and chloroplasts originated as independent unicellular organsims living in symbiosis with larger cells

217

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.

218

End plate potential

The depolarzation of the motor end plate on a muscle cell.

219

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.

220

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.

221

Enterokinase

A duodenal enzyme that activates trypsinogen (from the pancreas) to trypsin.

222

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.

223

Enzyme

A physiological catalyst. Enzymes are usually proteins, although some RNAs have catalytic activity.

224

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.

225

Epididymis

A long, coiled duct on the outside of the testis in which sperm mature.

226

Epiglottis

A flexible piece of cartilage in the larynx that flips downward to seal teh trachea during swallowing.

227

Epinephrine

A hormone produced and secreted by teh adrenal medulla that prolongs and increases teh effects of the sympathetic nervous system.

228

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.

229

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.

230

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.

231

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.)

232

Epitope

The specific site on an antigenic molecule that binds to a T cell receptor or to an antibody.

233

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.

234

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.

235

Erythrocyte

A red blood cell; they are filled with hemoglobin, and teh function of the erythrocytes is to carry oxygen in the blood.

236

Erythropoietin

A hormone produced and released by the kidney that stimulates the production of red blood cells by the bone marrow.

237

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.

238

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.

239

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).

240

Exclusion

The removal ( and usually the activation) of a viral genome from its host's genome.

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.

242

Excretion

The elimination of wastes from the body.

243

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).

244

Exocytosis

The secretion of a cellular product to the extracellular medium through a secretory vesicle.

245

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.

246

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).

247

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).

248

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.

249

Facultative anaerobe

An organism that will use oxygen (aerobic metabolism) if it is available, and that can ferment (anaerobic metabolism) if it is not.

250

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).

251

Fascicle

A bundle of skeletal muscle cells. Fascicles group together to form skeletal muscles.

252

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.

253

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.

254

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.

255

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.

256

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'.

257

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.

258

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.

259

Fibroblast

A generic connective tissue cell that produces fibers; the progenitor of all other connective tissue cell types.

260

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.

261

Fimbriae

Fingerlike projection of the uterin (fallopian) tubes that drape over the ovary.

262

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.

263

Flagella

A long, whip-like filament that helps in cell motility. Many bacteria are flagellated, and sperm are flagellated.

264

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.

265

Follicle

A developing oocyte and all of its surrounding (supporting) cells.

266

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.

267

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.

268

F1 generation

The first generation of offspring from a given genetic cross.

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

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.

273

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).

274

Gametogenesis

The formation of haploid gametes (sperm or ova) via meiosis.

275

Ganglion

A clump of gray matter (unmyelinated neuron cell bodies) found in the peripheral nervous system.

276

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.

277

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.

278

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.

279

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.

280

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.

281

Gene pool

The sum of all genetic material in a population.

282

Genetic code

The 'language' of a molecular biology that specifies which amino acid corresponds to which three-nucleotide group (codon).

283

Genome

All the genetic information in an organism; all of an organism's chromosomes.

284

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.

285

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.

286

Glomerulus

The ball of capillaries at the beginning of the nephron where blood filtration takes place.

287

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

288

Glycolipid

A membrane lipid consisting of a glycerol molecule esteried to two fatty acid chains and a sugar molecule.

289

Goblet cells

Unicellular exocrine glands found along the respiratory and digestive tracts taht secrete mucus.

290

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.

291

Gonadotropin releasing hormone (GnRH

A hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH and LH.

292

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.

293

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.

294

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.

295

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.

296

Gram-positive bacteria

Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.

297

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).

298

Gray matter

Unmyelinated neuron cell bodies and short unmyelinated axons.

299

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.

300

Guanine

One of the four aromatic bases found in DNA and RNA. Guanine is a purine; it pairs with cytosine.

301

Gustatory receptors

Chemoreceptors on the tongue that respond to chemicals in a food.

302

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.

303

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).

304

Haploid organism

An organism that has only a single copy of its genome in each of its cells. Haploid organisms possess no homolous chromosomes.

305

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.

306

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.

307

Helicase

An enzyme that unwinds the double helix of DNA and separates the DNA strands in preparation for DNA replication.

308

Hematocrit

The percentage of wholeblood made up of erythrocytes The typical hematocrit value is between 40-45%.

309

Hematopoiesis

The synthesis of blood cells (occurs in the red bone marrow)

310

Hemizygous gene

A gene appearing in a single copy in diploid organisms, e.g. X-linked genes in human males.

311

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.

312

Hemophilia

An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured.

313

Hemostasis

The stoppage of bleeding; blood clotting.

314

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.

315

Heterochromatin

DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.

316

Heterotroph

An organism that cannot make its own food, and thus must ingest other organisms.

317

Heterozygous

A genotype in which two different alleles are possessed for a given gene.

318

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.

319

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.

320

Histones

Globular protein that assist in DNA packaging in eukaryotes. Histones form octamers around which DNA is wound to form a nucleosome.

321

hnRNA

Heterogeneous nuclear RNA; the primary transcript made in eukaryotes before splicing.

322

Homeostasis

The maintenance of relatively constant internal conditions (such as temperature, pressure, ion balance, pH, etc.) regardless of external conditions.

323

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.

324

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.

325

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)

326

Humoral immunity

Specif ic defense of the body by antibodies, secreted into the blood by B-cells.

327

Hydroxyapatite

Hardy crystals consisting of calcium and phosphate that form the bone matrix.

328

Hyperpolarization

The movement of the membrane potential of a cell away from rest potential in a more negative direction.

329

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.

330

Hypophysis

The pituitary gland.

331

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.

332

Hypothalamus

The portion of the diencephalon involved in maintaining body homeostasis. the hypothalamus also controls the release of hormones from the pituitary gland.

333

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.

334

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.

335

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.

336

Ileum

The final section (approximately 55%) of the small intestine.

337

Implantation

The burrowing of a blastocyst (a developing embryo) into the endometrium of the uterus, typically occuring about a week after fertilizaiton.

338

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.

339

Inducible enzymes

An enzyme whose transcription can be stimulated by an abundance of its substrate (as opposed to repressible enzyme). Usually in catabolism.

340

Induction

The process by which neighboring cells can influence the determination (and subsequent differentiation) of a cell.

341

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).

342

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.

343

Innate immunity

General, non-specific protection to the body, including the skin (barrier), gastric acid, phagocytes, lysozyme, and complement.

344

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.)

345

Inspiration

The movement of air into the respiratory tract. Inspiration is an *active process*, requiring contraction of the diaphragm.

346

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).

347

Integral membrane protein

A protein embedded in the lipid bilayer of a cell. These are typicallly cell surface receptors, channels, or pumps.

348

Intercalcated discs

The division between neighboring cardiac muscle cells. Intercalcated discs include gap junctions, which allow the cells to function as a unit.

349

Intercostal muscles

Muscles located in between the ribs that play a role in ventilation.

350

Interleukin

A chemical secreted by a T cell (usually the helper Ts) that stimulates activation and proliferation of other immune system cells.

351

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.

352

Interneuron

A neuron found completely within the central nervous system. Interneous typically connect sensory and motor neurons, especially in reflex arcs.

353

Internodal tract

The portion of the cardiac conduction system between the SA node and the AV node.

354

Interphase

All of the cell cycle except for mitosis. Interphase includes G1, S phase, and G2.

355

Interstitial cell

Also called Leydig cells, these are teh cells within testes that produce and secrete testosteron. They are stimulated by luteinizing hormone (LH).

356

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.

357

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).

358

IPSP

Inhibitory postsynaptic potential; a slight hyperpolarization of the postysynaptic cell, moving the membrane potential of that cell further from threshold.

359

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.

360

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

361

Jejunum

The middle (approximtely 40%) of the small intestine.

362

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.

363

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.

364

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.

365

Kinase

An enzyme that phosphorylates something else. Kinases are frequently used in regulatory pathways, phosphorylating other enzymes.

366

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)

367

Labia

The folds of skin that enclose the vaginal and urethral openings of females.

368

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.

369

Lacteals

Specialized lymphatic capillaries in the intestines that take up lipids as well as lymph.

370

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.

371

Lacunae

Small cavities in the bone or cartilage that hold individual bones or cartilage cells.

372

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

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

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.

375

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).

376

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).

377

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).

378

Lawn

A dense grwoth of bacteria that covers the surface of a petri dish.

379

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.

380

Leak channel

An ion channel that is constitutively open, allowing the movement of teh ion across the plasma membrane according to its concentration gradient.

381

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.

382

Leukocyte

A type of white blood cell; leukocytes are either B or T cells and are involved in disease defense.

383

Ligament

A strong band of connective tissue that connets bones to one another.

384

Ligand

The specific molecule that binds to a receptor.

385

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.

386

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.

387

Lipoprotein

Large conglomerations of proteins, fats, and cholesterol that transport lipids in the bloodstream. (chylomicrons are a type of lipoprotein).

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

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).

390

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.

391

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.

392

Log phase

The period of exponential growth of bacterial population.

393

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).

394

Longitudinal muscle

The outer layer of smooth muscle in the wall of the digestive tract. When the longitudinal muscle contracts the tube shortens.

395

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).

396

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.

397

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*.

398

Lumen

The inside of the a hollow organ (e.g., the somach, intestines, bladder, etc.) or a tube (e.g., blood vessels, ureters, etc.)

399

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.

400

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.

401

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.

402

Lymph node

A concentrated region of white blood cells found along the vessels of the lympatic system.

403

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.

404

Lymphokine

A chemical secreted by a T cell (usually the helper Ts) that stimulates activation and proliferation of other immune system cells.

405

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.

406

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.

407

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.

408

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.

409

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.

410

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).

411

Maternal inheritance

Genes that are inherited only from the mother, such as mitochondrial genes (all organelles come only from the ovum).

412

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.

413

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.

414

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.

415

Medulla

The inner region of an organ, e.g., the renal medulla, the ovarian medulla, and the adrenal medulla, etc.

416

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.

417

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.

418

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.

419

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).

420

Meninges

The protective, connective tissue wrapping of the central nervous system (the dura mater, arachnoid mater, and pia mater).

421

Menopause

The perio dof tim ein a woman's life when ovulation and menstruation cease. Menopause typically begins in the late 40s.

422

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.

423

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.

424

Metaphase

The secon phase of mitosis. During metaphase chromosomes align at the center of the ell (the metaphase plate).

425

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).

426

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.

427

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.

428

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.

429

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.

430

Microvilli

Microscopic outward folds of the cells lining the small intestine; microvilli serve to increase the surface area of the small intestine for absorption.

431

Midbrain

The portion of the brain responsible for visual and auditory startle reflexes.

432

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.

433

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.

434

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.

435

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).

436

Monocistronic mRNA

mRNA that codes forsingle type of protein, such as is found in eukaryotic cells.

437

Monosaccharide

The monomer of a carbohydrate. Monosaccharides have the general chemical formula CnH2nOn, and common monosaccharides include glucose, fructose, galactose, and ribose.

438

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.

439

Motor end plate

The portion of the cell membrane at the neuromusclar junction; essentially the postsynaptic membrane at the synapse.

440

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.

441

Motor unit recruitment

A mechanism for increasing tension (contractile length) in a muscle by activating more motor units.

442

mRNA

Messenger RNA; the type of RNa that is read by a ribosome to synthesize protein.

443

Mucocilliary escalator

The layer of ciliated, mucus-covered cells in the respiratory tract.The cilia continually beat, sweeping contaminated mucus upward toward the pharynx.

444

Mucosa

The layer of epithelial tissue that lines body cavities in contact with the outside environment (respiratory, digestive, urinary, and reproductive tracts).

445

Mullerian ducts

Earlier embryonic ducts that can develop into femal internal genitalia in the absence of testosteron.

446

Mullerian inhibiting factor (MIF)

A substance secreted by embryonic testes that causes the regression of the Mullerian ducts.

447

Multipolar neuron

A neuron with a single axon and multiple dendrites; the most common type of neuron in the nervous system.

448

Mutualism

A form of symbiosis in which both organisms involved benefit from the association.

449

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.

450

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.

451

Myofibril

A string of sarcomeres with a skeletal muscle cell (hence smaller than myofiber). Each muscle cell contains hundreds of myofibirils.

452

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.

453

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.

454

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.

455

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.

456

NADH

The reduced form of NAD+ (nicotinamide adenine dinucleotide). This is the most common electron carrier in cellular respiration.

457

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.

458

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.

459

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.

460

Neuron

The basic functional and structural unit of the nervous system. The neuron is a highly specialized cell, designed to transmit action potentials.

461

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.

462

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.

463

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.

464

Nociceptors

Pain receptors. Nociceptors are found everywhere in the body except for the brain.

465

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).

466

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

467

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).

468

Nonsense mutation

A point mutation in which a condon that specifies an amino acid is mutated into a stop (nonsense) codon.

469

Norepinephrine

The neurotransmitter used by the sympathetic division of the ANS at the postganglionic (organ-level ) synapse.

470

Nuclear envelope

The membrane surrounding the DNA in eukaryotic cells made of two lipid bilayers.

471

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.

472

Nuclear pore

A protein channel in the nuclear envelope that llows the free passage of molecules smaller than 60 kD.

473

Nucleolus

A region within the nucleus where rRNA is transribed and ribosomes are partially assembled.

474

Nucleoside

A structure composed of a ribose molecule linked to one of the aromatic bases. In a deoxynucleoside, the ribose is replaced with deoxyribose.

475

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.

476

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.

477

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.

478

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..

479

Obligate aerobe

An organism that requires oxygen to survive (aerobic metabolism only).

480

Obligate anaerobe

An organism that can only survive in the absence of oxygen (anaerobic metabolism); oxygen is toxic to obligate anaerobes.

481

Okazaki fragments

Small fragments of DNa produced on the lagging strand during DNa replication, joined later by DNA ligase to form a complete strand.

482

Olfactory receptors

Chemoreceptors in the upper nasal cavity that respond to odo chemicals.

483

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.

484

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.

485

Operator

A specific DNA nucleotide sequence where transcriptional regulatory proteins can bind.

486

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.

487

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.

488

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.

489

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.

490

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.

491

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.

492

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.

493

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.

494

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.

495

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.

496

Osteoblast

A cell that produces bone.

497

Osteoclast

A phagocytic-like bone cell that breaks down bone matrix to release calcium and phosphate into the bloodstream.

498

Osteocyte

A mature, dormant osteoblast.

499

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).

500

Outer ear

The portion of the ear consisting of the pinna and the external auditory canal. The outer ear is separated from the middle ear by the tympanic membrane (the eardrum).