Mcat -- Biology

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cytoskeleton

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1. gives cell mechanical support, maintains shape, & functions in motility
2. composed of microtubules, microfilaments, and intermediate filaments

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facilitated diffusion

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1. passive movement of particles from a region of higher concentration using carrier molecules
2. does not require energy

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lysosome

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membrane-bound vesicle that contains hydrolytic enzymes used for intracellular digestion

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mitochondria

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1. site of aerobic resperation that provides the cell with a majority of its energy in the form of ATP
2. is a semiautonomous organelle enclosed by two membranes, with an intermmebrane space between the two membranes and mitochondrial matrix enclosed by the inner membrane

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obligate intracellular parasites

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organisms that require a host cell to express their genes and reproduce

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osmosis

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passive movement of water from a region or higher water concentration; diffusion of water

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simple diffusion

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passive movement of particles from a region of higher concentration to a region of lower concentration without the use of energy

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activation energy

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1. difference in potential energy between the initial state (reactants) and the transition state.
2. reactants must overcome the activation energy in order to undergo the reaction

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allosteric enzyme

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an enzyme with two or more active sites that can exist in more than one conformation, usually an active form or an inactive form

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apoenzyme

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an enzyme that requires cofactors in order to become catalytically active

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competitive inhibitor

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1. molecule that inhibits the activity of an enzyme by directly binding to the active site of the enzyme.
2. this type of inhibition is usually reversible and can be overcome by increasing the substrate concentration

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enzyme

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1. protein catalysts that accelerate reactions by reducing the activation energy without being consumed or altered by the reaction.
2. Note: enzymes affect only the rate of reaction and not the amounts of products formed

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free energy change

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1. difference in potential energy between the initial state (reactants) and the final state (products).
2. a negative ^G indicates a spontaneous reaction, whereas a positive ^G indicates a nonspontaneous reaction

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holoenzyme

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an active enzyme containing all necessary cofactors

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induced fit hypothesis

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1. theory of enzyme catalysis which states that the partial binding of a substrate to an enzyme alters the structure of the enzyme so that its active site becomes complementary to the structure of the substrate, enabling binding

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lock and key theory

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theory of enzyme catalysis stating that the active site's structure is complementary to the structure of the substrate

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Michaelis constant

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1. Km, is the ratio of the breakdown of an enzyme-substrate complex to its formation in simple michaelis-menton reactions.
2. Km is also half Vmax, and a low Km indicates a strong affinity between an enzyme and its substrate

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noncompetitive inhibitor

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1. molecule that inhibits the activity of an enzyme by binding to a regulatory site on the enzyme, thereby changing the conformation of the enzyme.
2. because these inhibitors do not directly compete with the substrate, increasing the substrate concentration usually has little effect on the catalytic rate

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regulator

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a molecule, other than the substrate, that can bind to the allosteric site of an enzyme and either increase its activity (allosteric activator) or decrease its activity (allosteric inhibitor)

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zymogen

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enzyme that must undergo processing before it can catalyze reactions

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citric acid cycle

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1. cycle begins when the two-carbon acetyl group from acetyl CoA combines with oxaloacetate to form citric acid
2. this product then proceeds through a series of reactions that result in the regeneration of oxaloacetate and the production of three NADH, one FADH2, and one GTP

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electron transport chain

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1. chain of cytochromes and other proteins in the inner membrane of the mitochondria that transfers electrons from NADH and FADH2 to oxygen.
2. the energy released from the series of oxidations is used to create a proton gradient, which ATP synthase then uses to synthesize ATP

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energy carriers (NAD+, NADP+, FAD)

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molecules involved in cell respiration that serve as energy stores, releasing energy when oxidized to NAD+, NADP+, and FAD

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facultative anaerobe

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an organism that makes ATP by aerobic respiration if oxygen is present, but that can switch to fermentation when oxygen is not available

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fatty acid activation

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fats must be activated using two ATP molecules before they can be converted into acetyl CoA and enter the citric acid cycle

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fermentation

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process by which the cell is able to replenish the NAD+ used during glycolysis by oxidizing NADH.
2. in this process, pyruvate (the product of glycolysis) is reduced by NADH to form ethanol (in yeast) or lactic acid (in humans)

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glycogen

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1. the form in which carbohydrates are primarily stored in the liver.
2. glycogen is easily converted to glucose-6-phosphate when the body needs it

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glycolysis

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1. through a series of enzymatic reactions in the cytoplasm, glucose is converted into two molecules of pyruvate.
2. the energy released in this process is used to produce a net yield of two ATP and two NADH molecules

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oxidative phosphorylation

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1. the coupling of the oxidation of NADH, NADPH, and FADH2 with the phosphorylation of ADP.
2. the electron transport chain utilizes oxidative phosphorylation to produce ATP

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pyruvate decarboxylation

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1. the first stage of cellular respiration.
2. pyruvate is oxidized to acetate, which then combines with coenzyme A to form acetytl CoA in the mitochondrial matrix.
3. this process results in the formation of one NADH per pyruvate molecule or two NADH per glucose molecule

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portal systems

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1. circulatory routes in which blood travels through two capillary beds before returning to the heart
2. some examples include the hepatic portal system, the renal system, and the hypophyseal portal system

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primary response

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1. the initial response to a specific antigen.
2. during a primary response, T & B lymphocytes are activated and specific antibodies and memory cells to the antigen are produced

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secondary response

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subsequent infections by antigens trigger a more immediate response by the memory cells produced during the primary response

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semilunar valves

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valves that prevent backflow of blood from the arteries back into the ventricles (aortic valve and pulmonic valve)

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substrate level phosphorylation

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1.the transfer of a phosphate group from an organic compound to ADP.
2. Glycolysis and the citric acid cycle utilize substrate level phosphorylation to produce ATP

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alleles

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genes coding for alternative forms of a given trait

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binary fission

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1. method of asexual reproduction by which prokaryotes divide.
2. the circular DNA molecule replicates and then moves to opposite sides of the cell
3. the cell then divides into two daughter cells of equal size

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centrosome

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the portion of the cell containing the centrioles

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chromatin

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1. chromosomes in their uncoiled active state
2. chromatin is not visible under a light microscope

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corona radiata

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1. outer layer of cells surrounding the oocyte
2. these cells are secreted by follicle cells

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crossing over

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1. the exchange of genetic material between chromosomes (usually homologous chromosomes) that occurs during prophase 1 of meiosis
2. crossing over aids in evolution and genetic diversity by unlinking linked genes

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diploid

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1. diploid cells have two copies of each chromosome, usually one from the mother and one from the father.
2. eukaryotic somatic cells are diploid

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disjunction

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the seperation of homologous chromosomes during anaphase 1 of meiosis

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dizygotic twins

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1. results when two ova are fertilized by two distinct sperm.
2. since the two resulting embryos develop from distinct zygotes, they do not have identical alleles

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follicle

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a multilayered sac of cells that protects and nourishes the developing ovum

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haploid

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1. haploid cells have only one copy of each chromosome.
2. germ cells in humans are haploid

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homologous chromosomes

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chromosomes in diploid cell that contain different alleles for the same trait at corresponding loci

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bacteriophages

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viruses that can only infect bacteria

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stabalizing selection

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type of natural selection where the normal phenotype is favored while those outside the norm are eliminated

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disruptive selection

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type of natural selection where both phenotype extremes are favored over the normal phenotype

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directional selection

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type of natural selection where one extreme phenotype is favored over the normal phenotype and other extreme phenotypes

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analogous structures

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similar structures that share a common function but not similar origins

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semiconservative replication

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a replicated molecule of DNA contains one strand of original DNA molecule (used as the template) and a newly synthesized DNA strand

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reverse transcriptase

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an enzyme in retroviruses that uses RNA strands as templates for synthesizing cDNA molecules