Biology MCAT Flashcards
Action Potential
A sharp change in the membrane potential of neurons or muscle cells caused by a change in the selective permeability of K+ and Na+ using ion-gated channels. Action potentials are all-or-none events
Activation Energy
The difference in potential energy between the inital state (reactants) and the transition state. Reactants must overcome the activation energy in order to undergo the reaction
Active Immunity
Immunity resultin from the produciton of antibodies during a previous infection or a vaccination
Active Transport
Movement of particles from a region of lower concentration to a region of higher concentration utilizing energy
ADH
Antidiuretic hormone (ADH), also known as vasopressin, acts on the collecting duct to increase water reabsorption. ADH is produced by the hypothalamus and stored in the posterior pituitary
Adrenal Cortex
Synthesizes and releases corticosteroids (including glucocorticoids and mineralcorticoids) when stimulated by adrenocroticotropic hormone (ACTH)
Adrenal Meduall
Synthesizes and releases epinephrine and norepinephrine, which stimulate an increase in the metabolic rate and blood glucose levels
Adrenocorticotropic Hormone
Synthesized and released by the anterior pituitary, ACTH stimulates the adrenal cortex to synthesize and secrete glucocoritcoids. ACTH is regulated by corticotrophin-releasing hormone (CRF) which is released by the hypothalamus
Afferent Neurons
Neurons that carry information to the central nervous system
Aldosterone
A steroid hormon produced in the adrenal cortex that is responsible for reabsorpiton of sodium and water and the excretion of potassium
Allantosis
The embryonic membrane that contains the growing embryo’s waster products
Allelels
Genes coding for alternative forms of a given trait
Allosteric Enzyme
An enzyme with two or more active sites that can exist in more than one conformation, usually an active form or an inactive form
Amino Acid Derived Hormones
Hormones that are synthesized from amino acids. Some amino acid derived hormones act via secondary messengers, while others act in a fashion similar to steroid hormones
Amnion
The innermost extraembryonic membrane that contains amniotic fluid in which the growing fetus is suspended
Analogous Structures
Similar structures that share a common funciton but not similar origins
Anterior Pituitary
Synthesizes and releases many vital hormones, including follicle-stimulating hormone, luteinizing hormone, adrenocorticotropic hormone, thyroid-stimulating hormone, prolactin, endorphins, and growth hormone (“FLATPED”). The anterior pituitary is under the hormonal control of the hypothalamus
Apoenzyme
An enzyme that requirees cofactors in order to become catalytically active
Appendicular Skeleton
The bones of the pelvis, the pectoral girdles, and the limbs
Arteries
Vessels that carry blood away from the heart. These vessels are muscular and do not have valvves
Ascending Limb of the Loop of Henle
Portion of the nephron not permeable to water. As the filtrate flows up the ascending limb through decreasing concentration of the intersitital fluid, Na+ is actively pumped out of the filtrate, decreasing filtrate concentration
Atria
The two thin-walle dupper chambers of the heart. The right atrium receives deoxygenated blood from the vena cava, while the left atrium receives oxygenated blood from the pulmonary vein
Atrioventricular Valves
Valves located between the atria and the centricles (tricuspid valve and mitral valve)
Axial skeleton
The skull, vertebral column, and bones of the chest
Axon Hillock
The portion of the neuron that connects the cell body (soma) to the axon. The impulses the neuron receives from all the dendrites are summed up at the axon hillock to determine whether an action potential will be initiated
Bacteriophages
Viruses that can only infect bacteria
Bile
An alkaline fluid synthesized in the liver, stored in the gall bladder, and released into the duodenum. Bile aids in the emulsification, digestion, and absorption of fats
Binary Fission
Metod of asexual reproduction by which prokaryotes divide. The ciruclar DNA molecule replicates and then moves to opposite sides of the cell. The cell then divides into two daughter cells of equal size
Blastulation
The process by which a morula develops into a blastula with a fluid-filled cavity called a blastocoel
Blood Antigens
Proteins found on the erythrocyte cell surface. Three antigens used to differentiate blood groups are A, B, and Rh. If a host organism is transfused with erythrocytes containing antigens that the host doe not have, an immune response will be triggered, such as in the case of erythroblastosis fetalis
Bohr Effect
Increasing teh concentration of H+ and CO2 reduces hemoglobin’s affinity for oxygen, allowing for the transfer of oxygen to cells that require it most
Calcitonin
Hormone synthesized and released by the thyroid gland that decreases plasma Ca2+ concentration
Capillaries
Blood vessels composed of a single layer of endothelial cells, facilitating exchange between the blood and interstitial fluid
Carbonic Anhydrase
Enzyme that catalyzes the conversion of carbonic acid to carbon dioxide and water as well as the formation of carbonic acid from carbon dioxide and water
Cardiac Output
The total volume of blood that left ventricle pumps into circulation per minute. The cardiac output can be increased by increasing either the heart rate or the stroke volume
Cardiac Sphincter
A valve between the esophagus and the stomach the prevents the content of the stomach from going back up through the esophagus
Cartilage
A firm, elastic, translucent connective tissue consisting of collagenous fibers embedded in chondrin. Produced by cells called chondrocytes. Cartilage is the principal component of embryonic skeletons and can harden and calcify into bone
Central Nervous System
The central nervous system consists of the brain and the spinal cord
Centrosome
The protion of the cell containing the centrioles
Chemical Digestion
Enzymatic breakdown of large molecules into smaller molecules
Chloroplast
The site of photosynthesis in plants. The chloroplast contains chlorophyll, is semiautonomous, and has two cell membrane
Cholecytoskinin
CCK is a hormone that is secreted by the duodenum in response to the presence of chyme. CCK stimulates the release of bile and pancreatic enzymes into the small intestine
Chorion
The outermost extraembryonic membrane; contributes to the formation of the placenta
Chromatin
Chromosomes in their uncoiled active states. Chromatin is not visibile under a light microscope
Chyme
Combination of partially digested food and acid that forms in the stomach
Ciliary Muscles
Muscular tissue attached to the lens that is used to control the lens’s shape
Citric Acid Cycle
The cycle begins when the two-carbon acetyl group from acetyl CoA combines with oxaloacetate to form citric acid. This product then proceeds througha series of reactions that result in the regeneration of oxaloacetate and the production of three NADH, one FADH2, and one GTP
Codon
Nonoverlapping group of three bases that code for a particular amino acid
Collecting Duct
Portion of te nephron permeable to water and ions. As the filtrate flows down the collecting duct through the increasing concentration of the intersitial fluid, the filtrate is concentrated further. The degree of water reabsorption in the collecting duct is controlled by the action of the hormones ADH and aldosterone
Compact bone
Much more dense than spongy bone, compact bone consists of havrsian systems (osteons)
Competitive inhibitor
Molecule that inhibits the activity of an enzyme by directly binding to the active site of the enzyme. This type of inhibition is usuallly reversible and can be overcome by increasing the substrate concentration
Cornea
Transparent coverin in front of the eye that refracts light and helps keep the eye in focus
Corona Radiata
Outer layer of cells surrounding the oocyte. These cells are secreted by follicle cells
Coronary Arteries
Blood vessels that supply the heart with oxygenated blood
Coronary Veins
Blood vessels that ransport deoxygenated blood from the heart toward the right atrium
Corpus Callosum
The crpus callosum connects the brain’s left hemisphere with its right hemisphere and correlates their activities
Corpus Luteum
Tissue that forms from the collapsed ovarian follicle. Produces and secretes progesteron and estrogen
Crossing Over
The exchange of genetic material between chromosomes (usually homologous chromosomes) that occurs during prophase I of meiosis. Crossing over aids in evolution and genetic diversity by unlinking linked genes
Cytoskeleton
The cytoskeleton gives the cell mechanical support, maintains shape, and functions in motility. It is composed of microtubules, micorfilaments, and intermediate filaments
Dendrite
As extension of the neuron that transmits impulses toward the cell body
Depolarization
A porcess that occurs when the voltage-gated Na+ channels open, allowing Na+ to rush into the cell and depolarize it
Dermis
The layer of skin beneath the epidermins that is subdivided into the papillary layer and the reticular layer. It contains the sweat glands, sense organs, blood vessels, and the bulbs of hair follicles, and is derived from the mesoderm
Descending Limb of the Loop of Henle
Portion of the nephron permeable only to water. The filtrate becomes more concentrated (loses water) as it travels through the descending limb due to the increasing concentration of interstitial fluid
Determinate Cleavage
A cleavage whose future differentiation pathways are determined
Diastole
The stage of the heart cycle in which the heart muscle relaxes and collects blood into its four chambers
Dihybrid Cross
A cross between two organisms where two distinct traits are being studied
Diploid
Diploid cells have two copis of each chromosome, usually one from the mother and one from the father. Eukaryotic somatic cells are diploid
Directional Selection
Type of natural selection where one extreme pheotype is favored over the normal phenotype and other extremem phenotypes
Disjunction
The separation of homologous chromosomes during anaphase I of meiosis
Disruptive Selection
Type of natural selection where both phenotypic extremes are favored over the normal phenotype
Dizygotic Twins
Results when two ova are fertilized by two different sperm. Since the two resulting embryos develop form distinct zygotes they do not have identical alleles.
DNA ligase
Enzyme that covalently links the Okazaki fragments together
DNA polymerase
An enzyme that polymerizes a complementary DNA strand in the 5’ to 3’ direction using a template DNA strand. A primer is necessary for DNA polymerase to initiate polymerization
Ductus Arteriosus
A shunt that connects the pulmonary artery to the aorta in order to bypass the fetal lung
Ductus venosus
A shunt that connects the umbilical vein to the inferior vena cava in order to bypass the fetal liver
Ectoderm
The outermost of teh three primary germ layers, which gives rise to the skin, and the nervous system
Efferent Neurons
neurons that carry information from the central nervous system to other parts of the body
Electron Transport Chain
A chain of cytochromes and other proteins in the inner membrane of teh mitochondria that transfers electrons form NADH and FADH2 to oxygen. The energy released from teh series of oxidations is used to create a proton gradient, which ATP synthase then uses to synthesize ATP
Endocrine Glands
Glands that synthesize and secrete hormones into the circulatory system. Examples include the hypothalamus, pituitary gland, pineal gland, thymus, pancrease, testes, ovaries, adrenal glands, thyroid gland, and parathyrodi glands
Endoderm
The innermost of the three primary germ layers, which gives rise to the linings of the digestive and respiratory tracts, and to parts of the liver, pancrease, thyroid, and bladder
Endometrium
The mucosal lining of the uterus where the embryo implants. Progesterone is necessary for the maintenance of the endometrium during pregnancy
Endorphins
Synthesized and released by the anterior pituitary, endorphins inhibit the perception of pain
Energy Carriers (NAD+, NADP+, FAD)
Molecules involved in cell respiration that serve as energy stores, releasing eneryg when oxidized to NAD+, NADP+, and FAD
Enzymes
Protein catalysts that accelerate reactions by reducing the activation energy without being consumed or altered by the reaction. Note the enzymes affect only the rate of reaction and not the amounts of products formed
Epidermis
The outermost layer of skin, which is composed of the following sublayers: stratum baslia, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. Serves as a protective barrier against microbial attack. Derived from the ectoderm
Epiglottis
A flap of cartilage that covers the glottis when swallowing food in order to prevent food particles from entereing the larynx
Episomes
Plasmids that have the ability to integrate into the host genome
Erythrocytes
The oxygen-carrying component of blood (red blood cells). These anaerobic cells, which lack organelles, are packed with hemoglobin and have a characteristic biconcave, dislike shape that facilitates gas exchange and mobility within blood vessels
Estrogen
Hormone syntheized and relazed by the ovaries, the ovarian folicles, the corpus luteum, and the placenta. Estrogen stimulates the development of the female reproductive tract and secondary sexual characteristics and is partly responsible for the LH spike that causes ovulation. Estrogen, along with progesterone produced by the placent during the second trimester of pregnancy, helps inhibit the oncset of a new menstrual cycle by blocking GnRH release
Exocrine Glands
Glands that synthesize and secrete substanes through ducts. The gall bladder is an example of an exocrine gland
Exons
Segments of coding eukaryotic mRNA that are spliced together and translated
Expiratory Reserve Volume
the amount of air that can be forcibly exhaled after a normal exhalation
Expressivity
The degree to which an organism expresses its genotype
Exteroceptor
Type of sensory receptor that monitors external signals such as light, sound, and temperature
Facilitated Diffusion
Passive movement of particles from a region of higher concentration to a region of lower concentration using carrier molecules. Does not require energy
Facultative Anaerobe
An organism that makes ATP by aerobic respiration if oxygen is present, but that can switch to fermentation when oxygen is not available
Fatty Acid Activation
Fats must be activated using two ATP molecules before they can be converted into acetyl CoA and enter the citric acid cycle
Fermentation
Process by which the cell is able to replenish the NAD+ used during glycolysis by oxidizing NADH. In this process, pyruvate (the product of glycolysis) is reduced by NADH to form ethanol (in yeast) or lactic acid (in humans)
Fibrin
Protein responsible for blood clotting
Filtrate
The material that passes from the blood vessles into Bowman’s capsule
Follice-Stimulating Hormone
Synthesized and released by the anterior pituitary, FSH stimulates maturation of ovarian follicles in females and maturation of the seminiferous tubules and sprem production in males. FSH is regulated by estrogen and gonadotropin-releasing hormone (GnRH)
Follicle
A multilayered sac of cells that protects and nourishes the developing ovum
Foramen Ovale
A shunt that connects the right atrium to the left atrium in order to bypass the fetal lung
Frame Shift Mutation
Mutation in which a number of nucleotides (except multiples of three) are either deleted or inserted. Such mutations lead to a shift in the DNA reading frame and often result in the translation of nonfunctional proteins
Free Energy Change
The difference in potential energy between the initial state (reactants) and the final state (products). A negative delta G indicates a spontaneous reaction, whereas a postive delta G indicates a nonspontaneous reaction
Frequency summation
The strengthening of contraction that results when the stimuli are so frequent that muscle cannot fully relax. The stronger contraction is due to the incorporation of more muscle fibers
Ganglia
A group of neural cell bodies in the peripheral nervous system
Gastric Glands
Located in the stomach; secrete HCl and various enzymes (eg. pepsin) when stimulated by gastrin
Gastrulation
The process by which a single-layer blastula becomes a three-layered gastrula
Genotype
The genetic makeup of an individual
GLomerulus
Network of capillaries within Bowman’s capsul that serves as the site of filtration. Blood cells and proteins are too large to be filtered, but ions, glucose, and amino acids readily pass into the filtrate
Glucagon
Produced and secreted by the alpha cells of the pancrease, glucagon increases blood glucose concentration by promotin gluconeogenesis and the conversion of glycogen to glucose in the liver