MCAT BIOLOGICAL SCIENCES

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

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 tissue a striated appearance. The A band does not shorten during muscle contraction.

A period of time following an action potential during which no additional action potential can be evoked regardless of the level of stimulation

The three glands in the male reproductive system that produce semen: the SEMINAL VESCICLES, the PROSTATE, and the BULBOURETHRAL GLANDS.

1. in the GI tract, organs play a role in digestion, but are not directly part of the alimentary canal. These include the LIVER, the GALLBLADDER, the PANCREAS, and the SALIVARY GLANDS

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

the enzyme that breaks down acetylcholine in the synaptic cleft.

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 fatty acid oxidation and protein catabolism

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

cells that make up exocrine glands and that secrete digestive enzymes in the salivary glands. acinar celle secrete saliva

a region at the head of a sperm cell that contains digestive enzymes which, when released during the acrosome reaction, can facilitate penetration of the corona radiata of the oocyte and fertilization

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

a localized change in a neuron's or muscle's membrane potential that can propagate itself away from its point of origin. Action potentials are an all or nothing process mediated by the opening of voltage gated Na+ and K+ channels when the membrane is brought to the threshold potential; opening od the Na+ channels causes a characteristic depolarization, while opening of the K+ channels repolarizes the membrane.

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

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

the movement of molecules through the plasma membrane against their concentration gradients. Active transport requires inout of cellular energy, often in the form of ATP. an exmaple is the Na+/K+ ATPase in the plasma membranes of all cells.

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 thymine (DNA) and uracil (RNA)

anterior pituitary gland; made of glandular tissue. makes and secretes 6 different hormones: FSH, LH, ACTH, TSH, prolactin, and GH. the anterior pituitary is controlled by releasing and inhibiting factors from the hypothalamus

fat cell

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

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

a tropic hormone produced by the anterior pituitary gland that targets the adrenal cortex, stimulating it to release cortisol and aldosterone.

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

a neuron that carrie information (action potentials) to the central nervous system; a sensory neuron

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

the principal mineralcorticoid secreted by the adrenal cortex. this steroid hormone targets the kidney tubules and increases renal reabsorption of sodium

also known as th GI tract or digestive tract, includes the long muscular tube that includes the mouth, esophagus,stomach, small intestine, and large intestine.

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

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

tiny sacs, with walls only a single cell thick, found at the end of the respiratoyu bronchiole tree. Alveoli are the sites of gas exchange in the respiratory system.

the monomer of a protein. amino acids have an amino group on one end of the moleculem,a carboxylic acid group on the other, and one of 20 different side chains

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

tRNA loading; the attachment of an amino acid to a tRNA (a specific interaction) requires two high energy phosphate bonds.

a tRNA with an amino acid attached. this is made by an aminoacyl-tRNA synthetase, and enzyme that is specific to the amino acid being attached

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

the characteristic of a molecule that has both polar (hydrophilic) and non polar (hydrophobic) regions examples include phospholipids and bile

an enzyme that digests starch into disaccharides. amylase is secreted by salivary glands and by the pancreas

the process of building complex structures out of simpler precursors (synthesizing proteins from amino acids)

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

that 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 (thus voluntary)

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

the third phase of meiosis I. during anaphase I, the replicated homologous chromosomes are separated (the tetrad is split apart) and pulled to opposite sides of the cell.

the third phase of meiosis II. during anaphase II, the sister chromatids are finallyt separated at their centromeres and pulled to opposite sides of the cell. note that anaphase II is identical to mitotic anaphase, except that the number of chromosomes was reduced by half during meiosis I

male sex hormones. testosterone is the male primary androgens

a normal blood protein produced by the liver, angiotensinogen 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 cause an increase in bp

something that acts to oppose the action of something else. for example, muscles that move a joint in opposite directions

also called inmmunoglobulins, antibodies are proteins secreted by activated b cell (plama cells ) that bind in a highly specific manner to foreign proteins (such as those found on the surface of pathogens or transplanted tissues). the foreign proteins are called antigens. antibodies do not destroy antigens directly, rather, they mark them for destruction through other methods, and can inactivate antigens by clumpling them together, or by covering necessary active sites.

a sequence of three nucleotides ( found in the anticodon loop of tRNA) that is complentary to a specific codon in mRNA. the codon to which the anticodon is complementary specifies the amino acid that is carried by that tRNA

also called vasopressin, this hormone is produced in the hypothalamus, but secreted by the posterior pituitary gland. it targets the kidney tubules, increasing their permeability to water, thus increasing water retention by the body.

ag, a molecule, usually a protein, capable of initiating an immune response, (antibody production)

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.

normal configuration of double stranded DNA in which the 5' end of one strand is paired with the 3' end of the other.

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

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

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

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.

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

blood vessel that carried blood away from the heart chambers. arteries have muscular walls to regulate blood flow and are typically high pressure vessels.

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

a protein complex found in the inner membrane of the mitochondria. it is essentially a channel that allows H+ ions to flow from the inter membrane space to the matrix (down the gradient produced by the enzyme complexes of the electron transport chain); as the H+ ions flow through the channel, ATP is synthsized from ADP and P_I

also known as the bundle of HIS, this is the first portion of the cardiac conduction system after the AV node.

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

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) valve separated the left atrium from the left ventricle. these valves close at the beginning of systole, preventing the backflow of blood from ventricles to atria, and producing the first heart sound

one of two small chambers in the heart that receive blood and pass it on to the ventricles. the right atrium receives deoxygenated blood from the body through the superior and inferior vena cavae and the left atrium receives blood from the lungs through the pulmonary veins.

first step in the viral infection. attachment of a virus to its host is very specific and is known as adsorption

tube that connects the middle ear cavity with the pharnyx. also known as the eustachian tube. its function is to equalize middle ear pressure with atmospheric pressure so that pressure is equal on both sides of the tympanic membrane.

an immune reaction directed against normal (necessary) cells. for example type I diabetes mellitus is an autoimmune rxn against B cells of the pancreas (destroying them and preventing insuling secretion, and against insulin itself)

the division of the peripheral nervous system the innervates and controls the visceral organs (everything but skeletal muscles) it is also known as the involuntary nervous system and can be divided into the sympathetic and parasympathetic nervous systems.

a chromosome that does not determine gender (is not a sex chromosome) humans have 2 sex chromosomes and 22 autosomes

an organism that can make its own food, typically using CO₂as a carbon source

A bacterium that cannot survive on minimal medium (glucaose alone) because it lacks the ability to synthesize a molecule it needs to live (typically an amino acid) auxotrpohs must have the needed substance (the auxillary trophic substance) added to the medium in order to survive. they are typically denoted by the substance they require followed by a minus sign) a bacterium that connot synthsize leucine would be a leucine auxotroph and would be indicated as leu^-

lacking a blood supply, for example cartilage

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

a bacterium having a rod like shape

virus that infects the bacteria

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

a layer of collagen fibers that separetes epithlial tissue from connected tissue.

the flexible membrane in the cochlea that supports the organ of corti (the structure that 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. this difference in structure allows the basilar membrane to transduce pitch

type of lymphocyte that can recognize (bind to) an antigen and secrete an antibody specific for that antigen. when activated by binding an antigen, B cells mature into plasma cells (that secrete antibody) and memory cells ( that patrol the body for future encounters with that antigen)

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

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 and serves to emulsify the fats for better digestion by lipases.

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 until it has doubled its cellular components, then it replicates its genome and splits into two.

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 neurons in the retina of the eye

a fluid filled sphere formed about 5 days after fertilization of an ovum that is made up of an outer ring of cells and an inner cell mass, this is the structure that implants in the endometrium of the uterus

the transfer of DNA or proteins from an electrophoesis gel to a nitrocellulose filter

tendency of certain factors to stabilize hemoglobin in the tense conformation, thus reducing its affinity for oxygen and enhancing the release of oxygen to the tissues. the factors include increased PCO₂ increased temperature, increased bisphosphoglycerate, and decreased pH. note that the Bohr effect shifts the oxyhemoglobin saturation to the RIGHT

non bony material that fills the hollow spaced inside the bones. red bone marrow is found in regions of the spongy bone and is the site of RBC production. yellow bone marrow is found in the diaphysis (shaft) of long bones, is mostly fat, and is inactive

region of the nephron the surrounds the glomerulus. the capsule collects the plasma the is filtered from the capilaries in the glomerulus.

very small air tubes in the respiratory system (diameter is 0.5-1mm) the walls of the bronchioles are made of smooth muscle to help regulate air flow

enzymes secreted by the mucosal cells lining the intestine. the brush border enzymes are disaccharides and dipeptidases that digest the smallest carbs and peptides into their respiective monomers.