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Flashcards in 1 Deck (382):
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 sacromere that extends to 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 mucle a striated appearance. The A band does not shorted 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 while K+ efflux)

4

Accessory glands

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

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 liver, the gallbladder, the pancreas, and 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 the Krebs cycle, produced primarily from the oxidation of pyruvate by the pyruvate dehydrogenase complex. However, acetyl-CoA is also produced during FA 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 the cells.

10

Acinar cells

Cells that make up exocrine glands and that secrete their products into ducts. For example, in the pancreas, acinar cells secrete digestive enzymes; in the salivary glands, acinar cells secrete saliva.

11

Acrosome

A region of the head of the sperm cell that contains digestive enzymes, which when released during the acrosomal 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 cytokinesis, pseudopod formation, and muscle contraction.

13

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.

14

Adenine

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

15

Adenohyphophysis

another name for anterior pituitary gland

16

Adrenal medulla

The inner region of the adrenal gland. The adrenal medulla is part of the sympathetic nervous system and releases epinephrine (adrenaline) and norepinephrine into the blood when stimulated. These hormones augment and prolong the effects of sympathetic stimulation in the body.

17

Adrenergic tone

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

18

Adrenocorticotropic hormone (ACTH)

A polypeptide tropic hormone (tropic means that it targets other endocrine glands). Produced by the anterior pituitary gland that targets the adrenal cortex, stimulating it to release cortisol and aldosterone.

19

Afferent arteriole

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

20

Afferent neuron

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

21

Albumin

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

22

Aldosterone

The principle mineralocorticoid secreted by the 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 and increased water comes out, increasing blood pressure indirectly.

23

Alimentary canal

aka the gastrointestinal tract of the digestive tract. The alimentary canal is the long muscular "tube" that includes the mouth, esophagus, stomach, small intestine, and large intestine.

24

Allosteric regulation

The modification of enzyme activity through interactions of molecules with specific sites on the enzyme other than the active site (called allosteric sites)

25

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.

26

Allele

A version of a gene. For example, the gene may be for eye color, and the alleles include those for brown eyes, blue eyes etc. At most, diploid organisms can possess only two alleles for a given gene. one on each of the two homologous chromosomes.

27

Amino acid

The monomer of a protein; amino acids have an amino group on one end of the molecule and a carboxylic acid group on the other.

28

Amino acid acceptor site

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

29

Aminoacyl tRNA

A tRNA with an amino acid attached. This is made by an aminoacyl-tRNA synthetase specific to the amino acid being attached.

30

Amnion

A sac filled with fluid (amniotic fluid) that surrounds and protects a developing embryo.

31

Amylase

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

32

Anabolism

The process of building complex structures out of simple precursors, e.g. synthesizing proteins from amino acids.

33

Analogous structures

Physical structures in two different organisms that have functional similarity due to their evolution in a common environment, but have different underlying structure. Analogous structures arise from convergent evolution.

34

Anal sphincter

The valve that controls the release of feces from the rectum. It has an internal part made of smooth muscle (thus involuntary) and an external part made of skeletal muscle (voluntary).

35

Anaphase

The 3rd phase of mitosis. During anaphase, replicated chromosomes are split apart at their centromeres (the sister chromatids are separated from each other) and moved to opposite sides of the cell.

36

Anaphase I

The 3rd phase of meiosis I. During anaphase I the replicated homologous chromosomes are separated (the tetrad is split) and pulled to opposite sides of the cell.

37

Anaphase II

The 3rd phase of meiosis II. During anaphase II the sister chromatids are finally separated at their centromeres and pulled to opposite sides of the cell. Note that anaphase II is identical to mitotic anaphase, except the number of chromosomes was reduced by half during meiosis i.

38

Androgens

Male sex hormones. Testosterone is the primary androgen.

39

Angiotensin

A normal blood protein produced by the liver, angiotensin is converted to angiotensin I by renin (secreted by the kidney when BP falls). Angiotensin I is further converted to Angiotensin II by ACE (angiotensin converting enzyme). Angiotensin II is a powerful systemic vasoconstrictor and stimulator of aldosterone release, both of which result in an increase in BP.

40

Antagonist

Something that acts to oppose the action of something else. For example, muscles that move a joint in opposite directions are said to be antagonists.

41

Anterior pituitary gland

aka the adenohypophysis. The anterior pituitary is made of gland tissue and makes and secretes six different hormones: FSH, LH, ACTH, prolactin, TSH, and growth hormone. The anterior pituitary is controlled by releasing and inhibiting factors from the hypothalamus.

42

Antibody (Ab)

Also called immunoglobins, the antibodies are proteins secreted by B-cells upon activation that bind in a highly specific manner to foreign proteins (such as those found on the surface of pathogens or transplated 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 inactivate antigens by clumping them together or by covering necessary active sites.

43

Anticodon

A sequence of three nucleotides (found in the 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.

44

Antidiuretic hormone (ADH)

Also called vasopressin, this hormone is produced in the hypothalamus and secreted by the posterior pituitary gland. It increases the kidney tubules permeability to water, and thus increases water retention by the body. Also raises blood pressure by inducing moderate vasoconstriction.

45

Antigen

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

46

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"

47

Antiparallel orientation

The normal configuration of the dsDNA in which the 5' end of one strand is paired with the 3' end of the other.

48

Antiporter

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

49

Aorta

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

50

Appendix

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

51

Aqueous humor

A thin, watery fluid found in the anterior segment of the eye (between the lens and the cornea). The aqueous humor is constantly produced and drained, and helps to bring nutrients to the lens and cornea, as well as to remove metabolic wastes.

52

Arousal

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

53

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 vessels.

54

A site

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

55

ATP synthase

A protein complex found in the inner membrane of the mitochondria. It is essentially a channel that allows H+ ions to flow from the intermembrane space to the matrix (down the gradient produced by the enzyme complexes of the etc); as the H+ ions flow through the channel, ATP is synthesized from ADP and Pi.

56

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.

57

Atrioventricular (AV) node

The second major node of the cardiac conduction system (after the SA node). The cardiac impulse is delayed slightly at the AV node, allowing the ventricles to contract just after the atria contract.

58

Atrioventricular valves

The valves in the heart that separate the atria from the ventricles. The tricuspid valve separates the right atrium from the right ventricle, and the bicuspid (mitral) valves separate the left atrium from the left ventricle. These valves close at the beginning of systole, preventing the back-flow of blood from the ventricles to atria, and producing the first heart sound.

59

Attachment

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

60

Auditory tube

The tube that connects the middle ear with the nasopharynx; also known as the Eustachian tube. Its function is to equalize middle ear pressure with atm pressure so that pressure on both sides of the tympanic membrane is equal.

61

Autoimmune reaction

An immune reaction directed against normal (necessary) cells. For example, diabetes melitus (typeI) is an autoimmune reaction directed against the beta cells of the pancreas (destroying them and preventing insulin secretion) and against insulin itself.

62

Autonomic

The division of the peripheral nervous system that innervates the and controls the visceral organs. It is also known as the involuntary nervous system and can be subdivied into sympathetic and parasympathetic.

63

Autosome

A chromosome that does not determine gender (not a sex chromosome). Humans have 2 sex chromosomes and 22 autosomes.

64

Autotroph

An organism that makes its own energy from light or inorganic oxidation.

65

Auxotroph

A bacterium that cannot survive on minimal medium (glucose alone) because it lacks the ability to synthesize a molecule it needs to live (typically an amino acid). Auxotrophs must have needed substance added to their medium in order to survive. They are typically denoted by the substance they require followed by a "-" sign in superscript.

66

Avascular

Lacking a blood supply; cartilage is an example of this.

67

Axon

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

68

Bacillus

A bacterium having a rod-like shape

69

Bacteriophage

A virus that infects a bacterium

70

Baroreceptor

A sensory receptor that responds to changes in pressure; for example, there are baroreceptors in the carotid arteries and the aortic arch that monitor bp.

71

Basement membrane

A layer of collagen fibers that separates epithelial tissue from connective tissue (example of epithelial cells in the digestive tract)- they are actual connective tissue.

72

Basilar membrane

The flexible membrane in the 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 window and long and flexible near the apex of the cochlea.

73

Bicarbonate

HCO3- This ion results from dissociation of carbonic acid, together with carbonic acid forms the major blood buffer system. Bicarbonate is also secreted by the pancreas to neutralize stomach acid in the intestines.

74

Bile

A green fluid made from cholesterol and secreted by the liver. It is stored and concentrated in the gallbladder. Bile is an amphipathic molecule that is secreted into the small intestine when fats are present. It serves to emulsify the fats for better digestion by lipases.

75

Binary fission

An asexual method of bacterial reproduction that serves only to increase the size of the population; there is no introduction of genetic diversity. The bacterium simply grows in size until it has doubled its cellular components, then it replicates its genome and splits in two.

76

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.

77

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.

78

Bohr effect

The tendency of certain factors to stabilize the hemoglobin in the tense conformation, thus reducing its affinity for oxygen and enhancing the release of oxygen to tissues. The factors include: increased PCO2, increase in temperature, increased BPG, and decreased pH. Bohr effect shifts with the oxy-hemoglobin saturation curve to the right.

79

Bone marrow

A non-bony material that fills the hollow spaces inside of bones. Red bone marrow is found in regions of spongy bone and is the site of red and white blood cell production. Yellow bone marrow is found in the diaphysis (shaft) of long bones, is mostly flat and is inactive.

80

Bowman's capsule

The region of the nephron that surrounds the glomerulus. The capsule collects plasma filtered from the capillaries in the glomerulus.

81

Bronchioles

Very small air tubes in the respiratory system. The walls of the bronchioles are made of smooth muscle (thus involuntary) to help regulate air flow.

82

Brush border enzymes

Enzymes secreted by the mucosal cells lining the intestine. The brush border enzymes are disaccharides and dipeptidases that digest the smallest peptides and carbohydrates into their respective monomers.

83

Bulbourethral glands

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 to neutralize any traces of acidic urine that may be harmful to sperm.

84

Calcitonin

A hormone produced by the C-cells of the thyroid gland that decreases serum calcium levels. It targets the bones (stimulates osteoblasts), the kidneys (reduces calcium reabsorption), and the small intestine (decreases calcium absorption).

85

Calcitriol

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

86

Calmodulin

A cytoplasmic Ca2+ binidng protein. Calmodulin is particularly important in smooth muscle cells, where binding of Ca2+ allows calmodulin to activate myosin light-chain kinase, the first step in smooth muscle contraction.

87

Canaliculus

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

88

Capacitation

An increase in the fragility of the membranes of sperm cells when exposed to the female reproductive tract. Capacitation is required so that the acrosomal enzymes can be released to facilitate fertilization.

89

Capilary

Smallest of all blood vessels, typically having a diameter just large enough for blood cells to pass through in single file. Capillaries have extremely thin walls to facilitate exchange of material between the blood and tissues.

90

Capsid

The outer protein coat of a virus.

91

Carbohydrates

Molecules made from monosaccharides that serve as the primary source of cellular energy. Carbohydrates can also act as cell surface markers.

92

Carbonic anhydrase

An enzyme present in the erythrocytes (as well as in other places) that catalyzes the conversion of CO2 and H2O into carbonic acid (H2CO3).

93

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 include the SA node, the internodal tract, the AV node, the AV bundle, the right and left bundle branches, and the Purkinje fibers.

94

Cardiac muscle

The muscle tissue of the heart. Cardiac muscle is striated, uninucleate, and under control of autonomic nervous system. Cardiac muscle is self-stimulatory, and autonomic control serves only to modify the intrinsic rate of contraction.

95

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.

96

Carrier protein

An integral membrane protein that undergoes a conformational change to move a molecule from one side of the membrane to another (uniporter, symporter, antiporter).

97

Cartilage

A strong connective tissue with varying degrees of flexibility. (1) Elastic cartilage is the most flexible, forming structures that require support but also need to bend (epiglottis and outer ear). (2) Hyaline cartilage is more rigid than elastic cartilage (ribs, respiratory tract, all joints). (3) Fibrocartilage is the least flexible, forms strong connections (pubic symphysis and intervertebral disks).

98

Catabolism

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

99

Catalase

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

100

Catalyst

Something that increases the rate of a chemical reaction by reducing the activation energy for that reaction. The free energy of the reaction remains unchanged.

101

cDNA

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

102

Cecum

The first part of the large intestine.

103

Cell surface receptor

An integral membrane protein that binds extracellular signaling molecules, such as hormones and peptides.

104

Central canal

The hollow center of an osteon, aka Haversian canal. The central canal contains blood vessels, lymphatic vessels, and nerves. Bone is laid down around the central canal in concentric rings called lamellae.

105

Central chemoreceptors

Receptors in the CNS that monitor the pH of cerebrospinal fluid to help regulate ventilation rate.

106

CNS

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

107

Centriole

A structure composed of a ring of nine microtube triplets, found in pairs of 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.

108

Centromere

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

109

Cerebellum

The region of the brain that coordinates motor control and smooth skeletal muscle activity.

110

Cerebral cortex

A thin (4mm) 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.

111

Cerebrospinal fluid

A clear fluid that circulates around through the brain and spinal cord that helps to physically support the brain and act as a shock absorber, and that also exchanges nutrients and wastes with the brain and spinal cord.

112

Ceruminous gland

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

113

Cervix

The opening to the uterus. The cervix is typically plugged with a sticky acidic mucus during non-fertile times (to form a barrier against the entry of pathogens). During ovulation the mucus becomes more water and alkaline to facilitate the sperm entry.

114

Channel protein

An integral protein that selectively allows molecules across the plasma membrane. (Ion channel, voltage-gated channel, ligand-gated channel).

115

Chemical synapse

A type of synapse at which a chemical (a neurotransmitter) is released from the axon of a neuron into the synaptic cleft. The chemical binds to receptors on the synaptic cleft on either another neuron or an organ.

116

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 the cerebrospinal fluid).

117

Chemotaxis

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

118

Chemotroph

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

119

Chief cells

Pepsinogen-secreting cells found at the bottom of the gastric glands.

120

Chitin

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

121

Cholecystokinin (CCK)

A hormone secreted by the small 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.

122

Cholesterol

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

123

Chondrocyte

A mature, cartilage cell.

124

Chorion

The portion of the placenta derived from the zygote.

125

Choroid

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

126

Chromosome

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

127

Chylomicron

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

128

Chyme

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

129

Chymotrypsin

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

130

Cilia

A hair-like structure on the cell surface composed of microtubules in a '9+2' arrangement (nine pairs of microtubules surrounding the 2 single microtubules in the center). The microtubules are connected with a contractile protein 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 mouse and nose.

131

Ciliary muscles

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

132

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).

133

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 cell surface receptors are associated with clathrin-coated pits at the plasma membrane binding of the ligand to the receptor triggering invagination (ex: cholesterol uptake via lipoprotein endocytosis).

134

Cleavage

The rapid mitotic division of a zygote that begins within 24-36 hours after fertilization.

135

Coccus

A bacteria having a round shape (plural= cocci).

136

Cochlea

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

137

Codominance

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

138

Codon

A group of 3 nucleotides that is specific for a particular amino acid, or that specifies 'stop translating'.

139

Coenzyme

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

140

Cofactor

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

141

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.

142

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 pass on its way to the ureter.

143

Common bile duct

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

144

Compact bone

A dense, hard type of bone constructed from osteons (at the microscopic level). Compact bone forms the diaphysis of the long bones, and the outer shell of the epiphyses and all other bones.

145

Competitive inhibitor

An enzyme inhibitor that competes with a substrate for binding at the active site of the enzyme. When the inhibitor is bound, no product can be made.

146

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.

147

Cones

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

148

Conjugation

A form of genetic recombination in bacteria in which plasmid and/or genomic DNA is transferred from one bacterium to the other though a conjugation bridge.

149

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 relatively few cells scattered around a great deal of extracellular material (matrix), and includes adipose tissue, bone, cartilage, the dermis of the skin, tendons, ligaments, and blood.

150

Convergent evolution

A form of evolution in which different organisms are placed into the same environment and exposed to the same selection pressures. This causes the organisms to evolve along similar lines. As a result, they may share functional, but not structural similarities (possessed different starting materials). Convergent evolution produces analogous structures.

151

Cooperativity

A type of substrate binding to a multi-active site enzyme, in which the binding of one substrate molecule facilitates the binding of subsequent substrate molecules. A graph of reaction rate vs. substrate concentration appears sigmoidal. Note that cooperativity can be found in other situates as well, ex. hemoglobin bind oxygen cooperatively.

152

Cornea

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

153

Corona radiata

The layer of granulosa cells that surround an oocyte after it has ovulated.

154

Coronary vessels

The blood vessels that carry blood to and from cardiac muscle. The coronary arteries branch off the aorta and carry oxygenated blood to the cardiac tissue. The coronary veins collect deoxygenated blood from the cardiac tissue, merge to form the coronary sinus, and drain into the right atrium.

155

Corpus callosum

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

156

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.

157

Cortex

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

158

Corticosteroids

Steroid hormones secreted from the adrenal cortex. The two major classes are the mineralcorticoids and glucocorticoids. Aldosterone is the principal mineralcorticoid, and cortisone is the principal glucocorticoid.

159

Cortisol

The principal glucocorticoid secreted from the adrenal cortex. This steroid hormone is released during stress, causing increased BG levels and reducing inflammation. The latter effect has had led to a clinical use of cortisol as an anti-inflammatory agent.

160

Creatine Phosphate

An energy storage molecule used by muscle tissue. The phosphate from the creatine phosphate can be removed and attached to an ADP to generate ATP quickly.

161

Cristae

The folds of the inner membrane of a mitochondrion.

162

Cross bridge

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

163

Crossing over

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

164

Cyclic AMP (cAMP)

A cyclic version of adenosine monophosphate where the phosphate is esterified to both the 5' and 3' carbons to form a ring. Cyclic AMP is an important intracellular signaling molecule, often called the 'second messenger'. It serves to activate cAMP-dependent kinases, which regulate the activity of other enzymes in the cell. Levels of cAMP are in part regulated by adenyl cyclase, the enzyme that makes cAMP, and the activity of adenyl cyclase is ultimately controlled by the binding of various ligands to cell surface receptors.

165

Cytokinesis

The phase of mitosis during which the cell physically splits into two daughter cells. Cytokinesis begins near the end of anaphase, and is completed during telophase.

166

Cytosine

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

167

Dendrite

A projection of the cell body of a neuron that receives a nerve impulse from a different neuron and sends the impulse to the cell body. Neurons can have one or several dendrites.

168

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.)

169

Depolarization

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

170

Dermis

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

171

Desmosome

A general cell junction, used primarily for adhesion.

172

Determination

The point during development at which a cell becomes committed to a particular fate. Note that the cell is not differentiated at this point. Determination can be due to cytoplasmic effects or to induction by neighboring cells.

173

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 (voluntary control), these stimulations occur autonomously.

174

Diaphysis

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

175

Diastole

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

176

Diastolic pressure

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

177

Diencephalon

The portion of the forebrain that includes the thalamus and hypothalamus.

178

Differentiation

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

179

Diffusion

The movement of a particle (the solute) in a solution from its high concentration to low concentration (down its concentration gradient.)

180

Diploid organism

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

181

Disaccharide

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

182

Distal convoluted tubule

The portion of the nephron tubule after the loop of Henle, but before the collecting duct. Selective reabsorption and secretion occur here, most notably regulated reabsorption of water and sodium.

183

Divergent evolution

A form of evolution in which the same organism is placed into different environments with different selective pressures. This causes organisms to evolve differently, to diverge from their common ancestor. The resulting species may share structural (but not necessarily functional) similarities; divergent evolution produces homologous structures.

184

DNA polymerase

Also called DNA pol, is the enzyme that replicates DNA. Eukaryotes have a single version of the enzyme, DNA pol; prokaryotes have three versions called DNA pol I, DNA pol II, DNA pol III.

185

Dominant

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

186

Dorsal root ganglion

A group of sensory neuron cell bodies found just posterior to the spinal cord on either side. A pari of root ganglia exists for each spinal nerve that extends from the spinal cord. The ganglia are part of the peripheral nervous system (PNS).

187

Downstream

Toward the 3' end of an RNA transcript (the 3' end toward the coding strand). Stop codons and (in eukaryotes) the pol-A tail are found 'downstream'.

188

Duodenum

The first (~5%) of the small intestine.

189

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.

190

Ectoderm

One of the three primary (embryonic) germ layers formed during gastrulation. Ectoderm ultimately forms external structures such as the skin, hair, nails, inner lining of the mouth and anus, as well as the entire nervous system.

191

Edema

Swelling of tissues, sometimes caused by inflammation letting in too many white blood cells (decreasing osmotic pressure at the end of the capillaries and not letting as much water back into the capillaries and staying in tissues).

192

Effector organ

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

193

Efferent arteriole

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

194

Efferent neuron

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

195

Ejaculation

A subphase of male orgasm, a reflex reaction triggered by presence of semen in the urethra. Ejaculation is a series of rhythmic contractions of the muscles near the base of the penis that increase the pressure in the urethra, forcing semen out.

196

Ejection fraction

The fraction of the end-diastolic volume ejected from the ventricles in a single contraction of the heart. The ejection fraction is normally around 60% of the end diastolic volume.

197

Elastin

A fibrous, connective-tissue protein that has the ability to recoil to its original shape after being stretched. Elastin is found in great amounts in lung tissue, arterial tissue, skin, and the epiglottis.

198

Electrical synapse

A type of synapse 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. (compare to chemical synapse)

199

Electron transport chain

A series of enzyme complexes found along the inner mitochondrial membrane. NADH and FADH2 are oxidized by these enzymes; the electrons are shuttled down the chain and are ultimately passed to oxygen and to produce water. The electric energy is used to pump H+ out of the mitochondrial membrane; the resulting H+ gradient is subsequently used to drive the production of ATP.

200

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 an embryo during this time period.

201

Emission

A subphase of male orgasm. Emission is the movement of sperm (via the vas deferens) and semen into the urethra in preparation for ejaculation.

202

Endocrine gland

A ductless gland that secretes a hormone into the blood

203

Endocrine system

A system of ductless glands that secrete chemical messengers into the blood

204

Endocytosis

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

205

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.

206

Endometrial cycle

The 28 days of the menstrual cycle as they apply to the events in the uterus. The endometrial cycle is aka the uterine cycle, and has 3 subphases: menstruation, the proliferative phase, and the secretory phase.

207

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 menstruation if a pregnancy does not occur.

208

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 become favorable again.

209

Endosymbiotic theory

The theory that mitochondria and chloroplasts originated as independent unicellular organisms living in symbiosis with larger cells.

210

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.

211

End plate potential

The depolarization of the motor end plate on a muscle cell

212

Enteric nervous system

The nervous system of the GI tract. It controls secretion and motility within the GI tract, and is linked to the CNS.

213

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.

214

Enterokinase

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

215

Envelope

A lipid bilayer that surrounds the capsid of an animal virus. The envelope is acquired as the virus buds out through the plasma of its host cell. Not all viruses possess an envelope.

216

Enzyme

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

217

Epidermis

The outermost layer of the skin. The epidermis is made of the epithelial tissue that is constantly dividing at the bottom; the cells migrate to the surface (dying along the way) to be sloughed off.

218

Epididymis

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

219

Epiglottis

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

220

Epinephrine

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

221

Epiphyseal plate

A band of cartilage (hyaline) found between the diaphysis and epiphyses of long bones during childhood and adolescence. Cell proliferation in the middle of the epiphyseal plate essentially forces the diaphysis and the epiphysis further apart, while the older cartilage at the ends of the plate is replaced with bone. This allows the bone to grow during childhood. The epiphyseal plate gets thinner and thinner the older a person gets, until finally it fuses to the diaphysis in late adolescence, preventing further elongation of the bones.

222

Enteric nervous system

The nervous system of the GI tract. It controls secretion and motility within the GI tract, and is linked to the CNS.

223

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.

224

Enterokinase

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

225

Epitope

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

226

Enzyme

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

227

Epidermis

The outermost layer of the skin. The epidermis is made of the epithelial tissue that is constantly dividing at the bottom; the cells migrate to the surface (dying along the way) to be sloughed off.

228

Epididymis

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

229

Epiglottis

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

230

Epinephrine

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

231

Epiphysis

One of the two ends of long bone. It has an outer shell made of compact bone and an inner core of spongy bone (red bone marrow, site of RBC formation).

232

Epistasis

A situation in which the expression of one gene prevents the expression of all allelic forms of another gene. E.g. The gene for male pattern baldness is epistatic to the hair color gene.

233

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, lining of urinary tract, etc.) or a glandular tissue (e.g. the liver, the pancreas, the ovaries, etc.)

234

Epitope

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

235

Excitatory postsynaptic potential (EPSP)

A slight depolarization of a postsynaptic cell, bringing the membrane potential of that cell closer to the threshold for an action potential.

236

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, gastric glands (acid, mucus, protease), the liver (bile), sebaceous glands (oil), and lacrimal glands (tears).

237

Erythrocyte

A RBC; they are filled with hemoglobin, and the function of the erythrocytes is to carry oxygen int he blood.

238

Erythropoietin

A hormone produced and released by the kidney that stimulates the production of RBCs by the bone marrow.

239

Estrogen

The primary female sex hormone. Estrogen stimulates the development of female secondary sex characteristics during adulthood, stimulates the development of a new uterine lining after menstruation, and stimulates mammary gland development during pregnancy.

240

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.

241

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).

242

Exclusion

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

243

Excitation-contraction coupling

The mechanism that ensures that skeletal muscle contraction does not occur without neural stimulation (excitation). At rest, 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 the cytosol of the muscle cell. Ca2+ binds to troponin, causing a conformational change int he troponin-tropomyosin complex that shifts it away form the myosin-binding sites. This allows myosin and actin to interact according to the sliding filament theory.

244

Fascicle

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

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 is secreted by a bacterium into its surrounding medium that help the bacterium compete with other species. Some exotoxins can cause serious disease in humans (botulism, tetanus, diptheria, TSS).

247

Expiration

The movement of air out of the respiratory tract. Expiration can be passive (caused by the relaxation of the diaphragm and elastic recoil of the lungs) or active (caused by contraction of the abdominal muscles, which increases the intra-abdominal pressure and forces the diaphragm up past its normal relaxed position).

248

Facilitated diffusion

Movement of a hydrophilic molecule across the PM 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 form (carries electrons) of FAD (flavin adenine dinucleotide). This is the other main electron carrier in cellular respiration (NADH is the most common).

251

Fast block to polyspermy

The depolarization of the egg PM upon fertilization, designed to prevent the entry of more than one sperm into the egg.

252

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 unnecessary. Feedback inhibition is the most common form of regulation int he body, controlling such things as enzyme reactions, hormone levels, BP, body temperature, etc.

253

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 allows glycolysis to continue under those conditions.

254

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 release of the acrosomal enzymes. Fertilization is a species-specific process, requiring binding of a sperm protein to an egg receptor.

255

F (fertility) factor

A bacterial extrachromosomal element that allows the bacterium to initiate conjugation. Bacteria that possess the F factor are known as F+ 'males'.

256

Fetal stage

The period of human development beginning at 8 weeks of gestation and lasting until birth (38-42 weeks). 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.

257

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.

258

Fibroblast

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

259

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.

260

Follicular phase

The first phase of the ovarian cycle, during which a follicle (an oocyte and its surrounding cells) enlarges and matures. This phase is under control of FSH (secreted form anterior pituitary) and typically lasts from day 1-14 of the menstrual cycle. The follicle secretes estrogen during this period.

261

F1 generation

The first generation of offspring from a given genetic cross.

262

Formed elements

The cellular elements of blood; erythrocytes, leukocytes, and platelets.

263

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 the amino acid sequence of the protein) is altered.

264

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).

265

Functional synctium

A tissue in which the cytoplasm of the cells are connected by gap junctions, allowing the cells to function as a unit. Cardiac smooth muscle tissues are examples of functional synctiums.

266

Gallbladder

A digestive accessory organ near the liver. The gallbladder stores and concentrates bile produced by the liver, and is stimulated to contract by cholecystokin (CCK).

267

Gametogenesis

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

268

Ganglion

A clump of gray matter (unmyelinated neuron cell bodies) found in the PNS.

269

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 the cytoplasms of both cells. Gap junctions allow small molecules to flow between the cells, and are important to cell-to-cell communication, for example, in relaying the action potential between cardiac muscle cells, and relaying nutrients between osteocytes.

270

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 G0 for these cells.

271

Gastrin

A hormone released by the 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.

272

Gastrulation

The division of the inner cell mass of a blastocyst (developing embryo) into three primary germ layers. Gastrulation occurs during weeks 2-4 of gestation.

273

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.

274

Gene pool

The sum of all genetic material in a population.

275

Genetic code

The 'language' of a molecular biology that specifies which amino acid corresponds to which 3-nucleotide group (codon).

276

Genome

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

277

Genotype

The combination of alleles an organism carries. In a homozygous genotype, both alleles are the same, whereas in a heterozygous genotype the alleles are different.

278

Gibbs free energy

The energy in a system that can be used to drive chemical reactions. If the change in free energy of a chemical reaction (the free energy of the products minus the free energy of the reactants) is negative, the reaction will occur spontaneously.

279

Glomerulus

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

280

Glucagon

A peptide hormone produced and secreted by the alpha cells of the pancreas. It targets primarily the liver, stimulating the breakdown of glycogen, thus increasing the BG levels.

281

Glycolipid

A membrane lipid consisting of a glycerol molecule esterified to 2 FA chains and a sugar molecules.

282

Goblet cells

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

283

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 packaging proteins.

284

Gonadotropin releasing hormone (GnRH)

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

285

Gonadotropins

Anterior pituitary tropic hormones FSH (follicle stimulating hormones) and LH (leutinizing hormone) that stimulates the gonads (testis and ovaries to produce gametes and to secrete sex steroids.

286

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 cyclase; this modifies the intracellular levels of the second messenger cAMP. When the GTP is hydrolyzed to GDP, the protein becomes inactive again.

287

Graafian follicle

A large, mature, ovarian follicle with a well-developed antrum and a secondary oocyte. Ovulation of the oocyte occurs from this type of follicle.

288

Gram-negative bacteria

Bacteria that have a thin peptidoglycan cell wall covered by an outer PM. They stain very lightly (pink) with gram stain. Gram negative bacteria are typically more resistant to antibiotics than Gram-positive bacteria.

289

Gram-positive bacteria

Bacteria that have a thick peptidoglycan cell wall, and no outer membrane. They stain very dark purple.

290

Granulosa cells

The majority of the cells surrounding an oocyte in a follicle. Granulosa cells secrete estrogen during the follicular phase of the ovarian cycle (before ovulation).

291

Gray matter

Unmyelinated neuron cell bodies and short unmyelinated axons.

292

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, and increases cell turnover rate in adults.

293

Guanine

One of the 4 aromatic bases found in DNA and RNA. Guanine is a purine; pairs with cytosine.

294

Gustatory receptors

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

295

Gyrase

A prokaryotic enzyme used to twist the single circular chromosome of prokaryotes upon itself to form supercoils. Supercoiling helps to compact prokaryotic DNA and make it sturdier.

296

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).

297

Hardy-Weinberg law

A law of population genetics that states that the frequency of alleles in a given gene pool do not change over time. There are 5 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 a 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.

298

hCG

Human Chorionic Gonadotropin, a hormone secreted by the trophoblast cells of a blastocyst (i.e. developing embryo) that prolongs the life of the corpus luteum, and thus increases the duration and amount of secreted progesterone. This helps 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.

299

Helicase

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

300

Hematocrit

The percentage of whole blood made up of erythrocytes. The typical hematocrit value is 40-45%.

301

Hematopoiesis

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

302

Hemizygous gene

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

303

Hemoglobin

A four subunit protein found in RBCs 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 4 oxygen molecules in a cooperative manner.

304

Hemophilia

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

305

Hemostasis

The stoppage of bleeding; blood clotting.

306

Hepatic portal vein

A vein connecting the capillary bed of the intestines with the capillary bed of the liver. This allows amino acids and glucose absorbed from the intestine to be delivered first to the liver for processing before being transported throughout the circulatory system.

307

Heterachromatin

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

308

Hardy-Weinberg law

A law of population genetics that states that the frequency of alleles in a given gene pool do not change over time. There are 5 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 a 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.

309

hCG

Human Chorionic Gonadotropin, a hormone secreted by the trophoblast cells of a blastocyst (i.e. developing embryo) that prolongs the life of the corpus luteum, and thus increases the duration and amount of secreted progesterone. This helps 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.

310

Helicase

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

311

Hematocrit

The percentage of whole blood made up of erythrocytes. The typical hematocrit value is 40-45%.

312

Hematopoiesis

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

313

Hemizygous gene

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

314

Hemoglobin

A four subunit protein found in RBCs 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 4 oxygen molecules in a cooperative manner.

315

Hemophilia

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

316

Hemostasis

The stoppage of bleeding; blood clotting.

317

Hepatic portal vein

A vein connecting the capillary bed of the intestines with the capillary bed of the liver. This allows amino acids and glucose absorbed from the intestine to be delivered first to the liver for processing before being transported throughout the circulatory system.

318

Heterachromatin

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

319

Heterotroph

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

320

Heterozygous

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

321

Hexokinase

The enzymes that catalyze the phosphorylation of glucose to form G6P in the first step of glycolysis. This is one of the main regulatory steps of this pathway. Hexokinase is feed-back inhibited by G6P

322

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.

323

Histones

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

324

hnRNA

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

325

Homeostasis

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

326

Homologous chromosomes

A pair of similar chromosomes that have the same genes in the same order, but may have different alleles of those genes. One of the pair of chromosomes came from the ovum and the other came from the sperm. Humans have 23 pairs of homologous chromosomes.

327

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.

328

Homozygous

A genotype in which two identical alleles are possessed for a given gene. The alleles can both be dominant (homozygous dominant) or both be recessive (homozygous recessive).

329

Humoral immunity

Specific defense of the body by antibodies, secreted in the blood by B-cells.

330

Hydroxyapatite

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

331

Hyperpolarization

The movement of the membrane potential of a cell away from the resting potential in a more negative direction. (after depolarization)

332

Hypodermis

Also 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.

333

Hypophysis

The pituitary gland

334

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 gland.

335

Hypothalamus

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

336

H zone

The region at the center of the A band of a sarcomere that is made up of myosin only. The H zone gets shorter(and may disappear) during muscle contraction.

337

Inner cell mass

The mass of cells in the blastocyst that ultimately give rise to the embryo and other embryonic structures (the amnion, the umbilical vessels, etc.)

338

Ileocecal valve

The sphincter that separates the final part of the small intestine (the ileum) from the front 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.

339

Ileum

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

340

Implantation

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

341

Incomplete dominance

A situation in which a heterozygote displays a blended version of the phenotypes 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.

342

Inducible enzymes

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

343

Interleukin

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

344

Inflammation

An irritation of a tissue caused by infection or injury. Inflammation is characterized by 4 cardinal symptoms: redness, swelling, heat, and pain.

345

Inhibin

A protein hormone secreted by sustenacular cells of the testes that act to inhibit the release of FSH and LH from the anterior pituitary.

346

Innate immunity

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

347

Interphase

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

348

Inspiration

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

349

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 the blood (lowering BG levels).

350

Integral membrane protein

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

351

Intercalated discs

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

352

Intercostal muscles

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

353

Interleukin

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

354

Jejunum

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

355

Interneuron

A neuron found completely within the CNS. Interneurons typically connect sensory and motor neurons, especially in reflex arcs.

356

Internodal tract

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

357

Interstitial cell

Also called Leydig cells, these are the cells within the testis that produce and secrete testosterone. They are stimulated by leutenizing hormone (LH).

358

Intron

A nucleotide sequence that intervenes between proton-coding sequences. In DNA these intervening sequences contain *regulatory sequences*, however, in RNA they are simply spliced out to form the mature (translated) transcript.

359

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).

360

IPSP

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

361

Iris

A pigmented membrane found just in front of the lens of the eye. In the center of the 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.

362

Islets of Langerhans

Also called "islet cells". These are the endocrine glands of the pancreas. Different cell types within the islets secrete insulin, glucagon, and somatostatin.

363

Juxtaglomerular apparatus (JGA)

A contact point between the afferent arteriole of the glomerulus and the distal convoluted tubule of the nephron. It is involved in regulated BP.

364

Lacunae

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

365

Keratin

A protein-based substance secreted by cells of the epidermis as they migrate outward. The keratin makes the cells tougher and helps make skin waterproof.

366

Kinase

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

367

Krebs cycle

The third stage of cellular respiration, in which acetyl-coA is combined with oxaloacetate to form citric acid. The citric acid is then decarboxylated twice and isomerized to recreate oxaloacetate. In the process, 3 molecules of NADH, 1 molecule of FADH2, and 1 molecule are formed (per acetyl -CoA).

368

Labia

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

369

Law of Independent assortment

Mendel's second law. States that genes found on different chromosomes, or genes found very far apart on the same chromosome (unlinked genes) sort independently of one another during gamete formation (meiosis).

370

Lacteals

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

371

Lawn

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

372

Lagging strand

The newly forming daughter strand of DNA that is replicated in a discontinuous fashion, via Okazaki fragments that are ultimately ligated together. The daughter 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

Luteinizing Hormone

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 testosterone (leydig cells).

375

Larynx

A rigid structure at the top of the trachea made completely out of cartilage. The larynx has 3 main functions 1. rigidness ensures trachea is held open for breathing 2. Epigloittis folds down to seal the trachea during swallowing, thus directing food to the esophagus and 3. this is where the vocal cords are found.

376

Law of segregation

Mendel's first law. The law of segregation states that two alleles of a given gene will be separate from one another during gamete formation (meiosis).

377

Lawn

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

378

Law of segregation

Mendel's first law. The law of segregation states that two alleles of a given gene will be separate from one another during gamete formation (meiosis).

379

Lawn

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

380

Length-tension relationship

The relationship of muscle length to its ability to generate strong contractions. Maximum tension is achieved at sarcomere lengths between 2.0 and 2.2 microns. Tension decreases outside of this range.

381

Luteal phase

The third phase of the ovarian cycle. After ovulation (follicle ruptures and releases secondary oocyte), the anterior pituitary hormones FSH and LH cause remaining parts of the follicle to transform into the corpus luteum. It produces progesterone (plays a vital role in making the endometrium receptive to implantation).

382

Luteinizing Hormone

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 testosterone (leydig cells).