biooo Flashcards
Term
Definition
5’ cap
a methylated guanine nucleotide added to the 5’ end of eukaryotic mRNA. The cap is necessary to initiate translation of mRNA
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.
A site
Amino-acyl tRNA site; the site on a ribosome where a new amino acid is added to a growing peptide.
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) z
Accessory glands
The three glands in the male reproductive system that reproduce semen: the seminal vesicles, the prostate, and the
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.
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.
Acetylcholine (Ach)
The neurotransmitter used throughout the parasympathetic nervous system as well as the neuromuscular junction.
Acetylcholinesterase (AChE)
The enzyme that breaks down acetylcholine in the synaptic cleft.
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.
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.
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
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.
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.
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.
Active site
The 3D site of an enzyme where substrates (reactants) bind and a chemical reaction is facilitated.
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.
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 with uracil (in RNA)
Adenohypophis
anterior pituitary gland
Adipocyte
fat cell
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.
Adrenergic tone
A constant input to the arteries that keeps them somewhat constricted to maintain a basal level of blood pressure.
Adrenocoricotropic hormone (ACTH)
A trop hormone produced by the anterior pituitary gand that targets the adrenal cortex, stimulating it to relase corisol and aldosterone.
Afferent arteriole
The small artery that carries blood toward the capillaries of the glomerulus.
Afferent neuron
A neuron that arries information (action potentials) to the central nervous system; a sensory neuron.
Albumin
A blood protein produced by the liver. Albumin helps to mantain blood osmotic pressure (oncotic pressure)
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).
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.
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.
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)
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.
Aminion
A sac filled with fluid (aminotic fluid) that surroudns and protects a developing embryo.
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.
Amino acid acceptor site
The 3’ end of a tRNA molecule that binds an amino acid. The nucleotide sequence at this end is CCA
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
Amphipathic
The characteristics of amolecule that has both polar (hydrophilic) and non-polar hydrophobic) regions, e.g. phospholipids, bile, etc.
Amylase
An enzyme that digests starch into disaccharides. Amylase is secreted by salivary glands and by the pancreas.
Anabolism
The process of bulidng complex structures out of simpler precursors, e.g. synthesizing protiens from amino acids.
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).
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.
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.
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.
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.
Androgens
Mal sex hormones. Testosteron is the primary androgen.
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.
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.
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.
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.
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.
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.
Antigen (Ag)
A molecule (usually a protein) capable of initiating an immune repsonse (antibody production).
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”
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
Antiporter
A carrier protein that transports two molecules acrss the plasma membrane in opposite directions.
Aorta
The largest artery in teh body; the aorta carries oxygenated blood away from the left ventricle of the heart.
Appendix
A mass of lymphatic tissue at the befenning of the large intestine that helps trap ingested pathogens.
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
Arousal
A function in the reproductive system, controlled by the parasympathetic nervous system, that includes erection (via dilation of erectile arteries) and lubrication.
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.
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
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.
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.
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).
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.
Attachment
The first step in viral infection. Attachemen of a virus to its host is very specific and is also known as adsorption.
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.
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.
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.
Autosome
A chromosome that does not determine gender (is not a sex chromosome). Humans have two sex chromsomes and 22 autosomes.
Autotroph
An organism that makes its own, typically using CO2 as a carbon source.
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)
Avascular
Lacking a blood supply; cartialge is an example of this
Axon
A long projection off the cell body of a neruon down which an action potential can be propagated.
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.
Bacilus
A bacterium having a rod-like shaped (plural = bacilli).
Bacteriophage
A virus that infects a bacterium.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
Calcitriol
A hormone produced from vitamin D that acts in essentially the same manner as parathyroid hormone.
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.
Canaliculus
Very small tube or channel, such as is found between lacunae (connecting them together) in compact bone.
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.
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.
Capsid
The outer protein coat of a virus (the whole coat)
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).
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).
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.
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.
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**.
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’.
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.
Catabolism
The process of breaking down large molecules into smaller precursors, e.g. digesion of starch into glucose.
Catalase
The primary enzyme in peroxisomes; catalse catalyzes the hydrolysis of hydrogen peroxide (H2O2) into water and oxygen.
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.
cDNA
Complementary DNA. DNA produced synthetically by reverse trascribing mRNA. Because of eukaryotic mRNA splicing, cDNA contains no inrons.
Cecum
The first part of the large intestine.
Cell surface receptor
An integral membrane proteint hat binds extracellular signaling molecules, suchas hormones and peptides.
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.
Central chemoreceptors
Receptors in the central nervous system that monitor the pH of cerebrospinal luid to help regulate ventilation rate.
Central Nervous System
The subdivision of the nervous system consisting of the brain and spinal cord.
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.
Centromere
A structure near the middle of eukaryotic chromosomes to which the fibers of the mitotic spindle attach during cell division.
Cerebellum
The region of teh brain that coordinates and smooth skeletal muscle activity.
Cerebral cortex
the cerebral hemispheres. The cerebral cortex is the conscious mind, and is functionally divided into four pairs of lobes: the frontal lobes, the parietal lobes, the temporal lobes, and the occipital lobes.
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.
Ceruminous gland
A gland that secretes a waxy product, found in the external ear canal.
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.
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’.
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.
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).
Chemotaxis
Movement that is directed by chemical gradients, such as nutrients or toxins. (seen in some bacteria)
Chemotroph
An organism that relies on a chemical source of energy (such as ATP) instead of light (which phototrophs).
Chief cells
Pepsinogen-secreting cells foudn at teh bottom of the gastric glands
Chitin
A poysaccharide found in the cell walls of fungi and in the exoskeletons of insects.
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.
Cholesterol
A large, ring shaped lipid found in cell membranes. Cholesterol is the precursor for steroid hormones, and is used to manufacture bile salts.
Chondrocyte
A mature, cartilage cell.
Chorion
The portion of the placenta derived from the zygote.
Choroid
The darkly pigmented middle layer of the eyeball, found between teh sclera (outer layer) and the retina (inner layer).
Chromosome
A single piece of double-stranded DNA; part of the genome of an organism. Prokaryotes have circular chromosomes and eukaryotes have linear chromosomes.
Chylomicron
A type of lipoprotein; the form in which absorbed fats from the intestines are transported to the circulatory system.
Chyme
Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.
Chymotrypsin
One of the main pancreatic proteases; it is activated (from chymotrypsinogen) by trypsin.
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.
Ciliary muscles
Muscles that help focus light on teh retin by controlling the curvature of the lens of the eye.
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).
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).
Cleavage
The rapid mitotic division of a zygot that being within 24-36 hours after fertilization
Coccus
A bacteria having a round shape (plural = cocci)
Cochlea
The curled structure in the inner ear that contains the membranes and hair cells that transduce sound waves into action potentials.
Codominance
A situation in which a heterozygote displays the phenotype associated with each of the alleles, e.g., human blood type AB.
Codon
A group of three nucleotides taht is specific for a particular amino acid, or that specifies ‘stop translating’
Coenzyme
An **organic molecuel taht associates non-covalently with an enzyme, and that is required for the proper functioning of the enzyme.
Cofactor
An **inorganic molecule that associates non-covalently with an enzyme and that is required for the proper functioning of the enzyme
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.
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.
Common bile duct
The duct that carries bile from the gallbladder and liver to the small intestine (duodenum).
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.
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.
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.
Cones
Photoreceptors in the retina of the eye that responds to bright light and provide color vision.
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.
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.
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.
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.
Cornea
The clear portion of the tough outer layer of teh eye ball, found over the iris and pupil
Corona radiata
The layer of granulosa cells taht surround an oocyte after is has been ovulated.
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.
Corpus callosum
The largest bundle of white matter (axons) connecting th two cerebral hemispheres.
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.
Cortex
The outer layer of an organ, e.g. the renal cortex, the ovarian cortex, the adrenal cortex, etc.
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.
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.
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.
Cristae
The folds of the inner membrane of a mitochondrion
Cross bridge
The connection of a mosin head group to an actin filament during muscle contraction (the sliding filament theory).
Crossing over
The exchange of DNA between paired homologus chromosomes (tetrads) during *prophase I* of meiosis.
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.
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.
Cytosine
One of the four aromatic bases found in DNA and RNA. Cytosine is a pyrimidine; it pairs with guanine.
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!
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.)
Depolarization
The movement of teh membrane potential of a cell away from rest potential in a more positive direction.
Dermis
A layer of connective tissue underneath the epidermis of the skin. The dermis contains blood vessels, lymphatic vessels, nerves, sensory receptors, and glands.
Desmosome
A general cell junction, used primarily for adhesion.
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.
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.
Diaphysis
The shaft of a long bone. The diaphysis is hollow and is made entirely from compact bone.
Diastole
The perio of time during which the ventricles of the heart are relaxed.
Diastolic pressure
The pressure measured in the arteries while the ventricles are relaxed (during diastole).
Diencephalon
The portion of theforebrain that includes the thalamus and hypothalamus.
Differentiation
The specialization of cell types, especially during the embryonic and fetal development.
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).
Diploid organism
An organism that has two copies of its genome it each cell. The paired genomes are said to be homologous.
Disaccharide
A molecule composed of two monosaccharides. Common disaccharides include maltose, sucrose, and lactose.
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.
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.
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.
Dominant
The allele in a heterozygous genotype that is expressed; the phenotype resulting from either a heterozygous genotype or a homozygous dominant genotype.
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).
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.’
Duodenum
The first (approximately 5%) of the small intestinte.
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.
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.
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).
Effector organ
The organ that carries out teh command sent along a particular motor neuron
Efferent arteriole
The small artery that carries blood away from the capillaries of the glomerulus.
Efferent neuron
A neuron that carries information (action potentials) away from the central nervous system; a motor neuron.
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.
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.
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.
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.
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.
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.
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.
End plate potential
The depolarzation of the motor end plate on a muscle cell.
Endocrine gland
A ductless gland that secretes a hormone into the blood
Endocrine system
A systme of ductless glands taht secrete chemical messengers (into) the blood - has to be into the blood.
Endocytosis
The uptake of material into a cell, usually by invagination. See also ‘phagocytosis’, pinocytosis, and receptor-mediated endocytosis..
Endoderm
One of the three primary (embryonic) germ layers
Endometrial cycle
formed during gastrulation. Endoderm ultimately forms internal structures, such as the inner lining of the GI tract and glandular organs.
Endometrium
The 28 days of the menstrual cycle as they apply to the events in the uterus. The endometrial cycle is also known as the uterine cycle, and has the three subphases: menstruation, the proliferative phase, and the secretory phase.
Endospore
The inner epithelial lining of the uterus that thickens and develops during the menstrual cycle, into which a fertilized ovum can implant, and which sloughs off during menstration if a pregnancy does not occur.
Endosymbitoic theory
the theory that mitochondria and chloroplasts originated as independent unicellular organsims living in symbiosis with larger cells
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.
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.
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.
Enterokinase
A duodenal enzyme that activates trypsinogen (from the pancreas) to trypsin.
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.
Enzyme
A physiological catalyst. Enzymes are usually proteins, although some RNAs have catalytic activity.
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.
Epididymis
A long, coiled duct on the outside of the testis in which sperm mature.
Epiglottis
A flexible piece of cartilage in the larynx that flips downward to seal teh trachea during swallowing.
Epinephrine
A hormone produced and secreted by teh adrenal medulla that prolongs and increases teh effects of the sympathetic nervous system.
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.
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.
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.
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.)
Epitope
The specific site on an antigenic molecule that binds to a T cell receptor or to an antibody.
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.
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.
Erythrocyte
A red blood cell; they are filled with hemoglobin, and teh function of the erythrocytes is to carry oxygen in the blood.
Erythropoietin
A hormone produced and released by the kidney that stimulates the production of red blood cells by the bone marrow.
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.
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.
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).
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.
Exclusion
The removal ( and usually the activation) of a viral genome from its host’s genome.
Excretion
The elimination of wastes from the body.
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).
Exocytosis
The secretion of a cellular product to the extracellular medium through a secretory vesicle.
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.
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).
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).
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’.
F1 generation
The first generation of offspring from a given genetic cross.
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.
Facultative anaerobe
An organism that will use oxygen (aerobic metabolism) if it is available, and that can ferment (anaerobic metabolism) if it is not.
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).
Fascicle
A bundle of skeletal muscle cells. Fascicles group together to form skeletal muscles.
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.
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.
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.
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.
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.
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.
Fibroblast
A generic connective tissue cell that produces fibers; the progenitor of all other connective tissue cell types.
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.
Fimbriae
Fingerlike projection of the uterin (fallopian) tubes that drape over the ovary.
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.
Flagella
A long, whip-like filament that helps in cell motility. Many bacteria are flagellated, and sperm are flagellated.
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.
Follicle
A developing oocyte and all of its surrounding (supporting) cells.
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.
Formed elements
The cellular elements of blood; erythrocytes, leukocytes, and platelets.
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.
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).
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.
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.
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.
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).
Gametogenesis
The formation of haploid gametes (sperm or ova) via meiosis.
Ganglion
A clump of gray matter (unmyelinated neuron cell bodies) found in the peripheral nervous system.
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.
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.
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.
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.
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.
Gene pool
The sum of all genetic material in a population.
Genetic code
The ‘language’ of a molecular biology that specifies which amino acid corresponds to which three-nucleotide group (codon).
Genome
All the genetic information in an organism; all of an organism’s chromosomes.
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.
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.
Glomerulus
The ball of capillaries at the beginning of the nephron where blood filtration takes place.
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
Glycolipid
A membrane lipid consisting of a glycerol molecule esteried to two fatty acid chains and a sugar molecule.
Goblet cells
Unicellular exocrine glands found along the respiratory and digestive tracts taht secrete mucus.
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.
Gonadotropin releasing hormone (GnRH
A hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH and LH.
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.
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.
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.
Gram-positive bacteria
Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.
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).
Gray matter
Unmyelinated neuron cell bodies and short unmyelinated axons.
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.
Guanine
One of the four aromatic bases found in DNA and RNA. Guanine is a purine; it pairs with cytosine.
Gustatory receptors
Chemoreceptors on the tongue that respond to chemicals in a food.
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.
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.
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).
Haploid organism
An organism that has only a single copy of its genome in each of its cells. Haploid organisms possess no homolous chromosomes.
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.
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.
Helicase
An enzyme that unwinds the double helix of DNA and separates the DNA strands in preparation for DNA replication.
Hematocrit
The percentage of wholeblood made up of erythrocytes The typical hematocrit value is between 40-45%.
Hematopoiesis
The synthesis of blood cells (occurs in the red bone marrow)
Hemizygous gene
A gene appearing in a single copy in diploid organisms, e.g. X-linked genes in human males.
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.
Hemophilia
An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured.
Hemostasis
The stoppage of bleeding; blood clotting.
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.
Heterochromatin
DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.
