MCAT Biology Flashcards
Oligodendrocytes
Cells that produce myelin in the central nervous system.
Myelin sheath
Electrically insulating substance that surrounds axons, secreted by Schwann cells and oligodendrocytes.
Anaphase
The mitotic phase involving the separation of chromosomes.
Cell wall
The cell’s protection from external stimuli and desiccation.
Heterozygotes
Organisms containing two different alleles for the same gene on corresponding chromosomes.
Neural crest cells
Cells at the tip of the neural fold; this group of cells gives rise to many components of the peripheral nervous system.
Microfilaments
Solid rods of actin that are involved in cell movement and cell wall support.
Appendicular skeleton
The bones of the pelvis, pectoral girdles, and limbs.
Cholecystokinin
A hormone that is secreted by the duodenum in response to the presence of chyme. It stimulates the release of bile and pancreatic enzymes into the small intestine.
Inversion
A form of chromosomal rearrangement in which a portion of a chromosome breaks off and rejoins the same chromosome in the reverse position.
Adrenal medulla
Synthesizes and releases epinephrine and norepinephrine, which stimulates an increase in the metabolic rate and blood glucose levels.
Bacteriophages
Viruses that can infect bacteria.
Cornea
Transparent covering in front of the eye that refracts light and helps keep the eye in focus
Osmoregulation
Maintenance of water and solute concentrations.
Humoral immunity
The synthesis of specific antibodies by activated B-cells in response to an antigen. These antibodies bind to the antigen and either clump together to become insoluble or attract other cells that engulf them.
Exteroceptor
Type of sensory receptor that monitors external signals such as light, sound, and temperature.
Endometrium
The mucosal lining of the uterus where the embryo implants. Progesterone is necessary to maintain it during pregnancy.
Iris
Muscular tissue in the eye that controls the amount of light allowed in through the pupil.
Penetrance
The percentage of people in a population with a certain genotype who express the associated phenotype.
Microtubules
Structures that maintain cell shape, form the spindle, and provide tracks along which organelles can move. They also compose cilia and flagella.
Gametocyte
A cell from which gametes form by meiotic division, especially a spermatocyte or an oocyte.
Enzymes
Catalysts (usually proteins) that accelerate reactions by reducing the activation energy without being consumed or altered by the reaction.
Capillaries
Blood vessels composed of a single layer of endothelial cells, facilitating exchange between the blood and interstitial fluid.
Homozygotes
Organisms containing two identical copies of the same gene on corresponding chromosomes.
Glycogen
The primary form in which carbohydrates are stored in the liver.
Directional selection
Type of natural selection where one extreme phenotype is favored over the mean phenotype and other extreme phenotypes.
Parthenogenesis
The development of an unfertilized egg into an adult organism.
Autotroph
An organism that can harness sunlight to create energy via photosynthesis.
Zygote
A fertilized egg.
Fluid mosaic model
A model that states that a cell membrane consists of a phospholipid bilayer with proteins embedded throughout.
Intramembranous ossification
This is the transformation of mesenchymal tissue into bone.
Lock and key theory
Theory of enzyme catalysis stating the active site’s structure is complementary to the structure of the substrate.
Mendel’s Law of Independent Assortment
The alleles of different genes assort independently during meiosis. We now know that this is true only for unlinked genes.
Helicase
An enzyme that unwinds the double helix of a DNA molecule and separates the two strands, allowing replication to take place.
Coronary arteries
Blood vessels that supply the heart with oxygenated blood
Adrenocorticotropic hormone
Synthesized and released by the anterior pituitary, it stimulates the adrenal cortex to synthesize and secrete glucocorticoids.
Seminiferous tubules (testes), epididymis, vas deferens, ejaculatory duct, (nothing), urethra, penis
Name the structures of the male reproductive tract using the Kaplan acronym (SEVEN UP).
Fovea
The region of the retina with a high density of cones.
Osmosis
The passive movement of water; diffusion of water.
Pyloric glands
Glands located in the walls of the stomach that secrete the hormone gastrin in response to certain substances in food.
Ventricles
The muscular lower chambers of the heart.
Genotype
Genetic makeup of an individual
Testosterone
Hormone secreted by the interstitial cells of the testes. It is responsible for embryonic sexual differentiation, male sexual development, and maintenance of masculine secondary sexual characteristics.
Lagging strand
During DNA replication, the strand of DNA that is synthesized in small fragments and then ligated together.
Homeostasis
The maintenance of a stable internal environment.
Diploid
Cells that have two copies of each chromosome, like somatic eukaryotic cells.
Large intestine
Section of the GI tract that consists of the cecum, colon, and rectum. The major function is to absorb salts and water.
Rough endoplasmic reticulum
Serves as an attachment point for ribosomes, which functions in protein synthesis.
Autonomic nervous system
Division of the peripheral nervous system that is responsible for involuntary movement
Monosynaptic reflex
Reflex pathway that has only one synapse between the sensory neuron and the motor neuron.
Posterior pituitary
Stores and releases hormones synthesized in the hypothalamus. Release of hormones is triggered by an action potential that originates in the hypothalamus.
Efferent neurons
Neurons that carry information from the central nervous system to other parts of the body.
Negative pressure breathing
The contraction of the diaphragm and the intercostal muscles increases the volume of the thoracic cavity, reducing the pressure in the intrapleural space.
Nephron
The functional unit of the kidney.
Purines
Adenine and guanine. They have characteristic bicyclic nitrogenous bases and pair with pyrimidines in double-stranded DNA.
Diastole
The stage of the heart cycle in which the heart muscle relaxes and collects blood into its four chambers.
Osteoclasts
Cells in the bone matrix that are involved in bone degradation.
Hypothalamus
Structure responsible for visceral functions such as hunger, thirst, and sex drive.
Expressivity
The degree to which an organism expresses its genotype.
Spermatozoa
Mature sperm specialized for transporting a male’s genetic information to the ovum.
Glomerulus
Network of capillaries within the Bowman’s capsule 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.
Arteries
Vessels that carry blood away from the heart. These vessels are muscular and do not have valves.
Haploid
Cells that have only one copy of each chromosome, such as human gametes.
DNA ligase
Enzyme that covalently links the Okazaki fragments together during DNA replication
Repressible system
A system that is normally “turned on” but can be inactivated by the addition of a repressor or corepressor.
Semen
The fluid discharged during ejaculation, consisting of sperm cells and seminal fluid.
Small intestine
It can be divided into three sections; the duodenum, jejunum, and ileum. Most digestion takes place in the duodenum, and most absorption takes place in the jejunum and the ileum.
Alleles
Genes coding for alternative forms of a given trait.
Disjunction
The separation of homologous chromosomes during anaphase I of meiosis.
Vestigial structures
Structures that have lost ancestral function, like the human tailbone.
Transcription
The process whereby mRNA is synthesized from a DNA template.
Synaptic terminals
Ends of axons that form one side of the synaptic cleft; the location where neurotransmitters are stored.
Proximal convoluted tubule
Site where glucose, amino acids, and other important organic molecules are reabsorbed from the filtrate into the interestitial fluid. It lies in the cortex of the kidney.
Cerebellum
Part of the brain that is responsible for coordination.
Adaptive radiation
The emergence of a number of distinct lineages from a single ancestral species.
Cytoskeleton
Gives cell mechanical support, maintains cell shape, and functions in cell motility. Composed of microtubules, microfilaments, and intermediate filaments.
Transverse tubules
A system of structures that provides channels for ion flow throughout the muscle fibers to facilitate the propagation of electrical signals from the nervous system.
Prolactin
A hormone synthesized and released by the anterior pituitary that stimulates milk production and secretion in female mammary glands.
Tetrad
Four chromatids that result when a pair of homologous chromosomes synapse during prophase I of meiosis.
Veins
Vessels that carry blood toward the heart. They have thin walls and have valves to prevent backflow.
Golgi apparatus
Receives vesicles from the smooth ER, modifies them, and repackages them into vesicles for distribution.
Right atrium, tricuspid valve, right ventricle, pulmonary arteries, pulmonary capillaries, pulmonary veins, left atrium, bicuspid valve, left ventricle, aorta, arteries, arterioles, vapillaries, venules, veins, vena cava
Starting with the right atrium, trace the path of blood flow throughout the body.
Placenta
An organ formed by the uterus and extraembryonic membranes of the fetus. It contains a network of capillaries through which exchange between the fetal and maternal circulations take place.
Medulla oblongata
The part of the brain that controls many basic, autonomic functions, such as breathing and heart rate.
Pyrimidines
Cytosine and thymine. They have characteristic monocyclic nitrogenous bases and pair with purines in double-stranded DNA.
Ganglion
A group of neural cell bodies in the peripheral nervous system.
Nodes of Ranvier
Gaps between segments of myelin sheath where action potentials can propagate, allowing for saltatory conduction.
Inner cell mass
The group of cells in a blastocyst that develop into the embryo.
Cerebral cortex
Processes and integrates sensory input and motor response, and controls memory.
Inducible system
A system in which a repressor bound to an operator prevents transcription. Addition of inducers can activate it by preventinr the repressor from binding to the operator.
Zymogen
Enzyme that must undergo processing before it can catalyze reactions
Fatty acid activation
The usage of two ATP molecules to convert fats into acetyl CoA for usage in the citric acid cycle.
Hyperpolarization
State where the potential across the membrane is more negative than the resting potential.
Polar body
A small, short-lived haploid cell created during oogenesis that receives very little cytoplasm, organelles, and nutrients.
Phenotype
The physical manifestation of an individual’s genotype
Retrovirus
An RNA virus that codes for the enzyme reverse transcriptase, which uses the RNA as a template for DNA synthesis.
Telophase
The mitotic phase where cytokinesis occurs.
Depolarization
A process that occurs when the voltage-gated Na+ channels open, allowing Na+ to rush into the cell.
Residual volume
The amount of air that must remain in the lung at all times in order to prevent collapse
Ribonucleic acid
Similar to DNA but the sugar deoxyribose is replaced with the sugar ribose, and adenine pairs with uracil instead of thymine.
Incomplete dominance
Describes a situation in which an organism heterozygous for a trait will have a phenotype that is intermediate both alleles.
Sarcoplasmic reticulum
A modified form of endoplasmic reticulum, which stores calcium that is use to trigger contraction when muscle is stimulated.
Pyloric sphincter
A valve between the stomach and the small intestine that regulates the flow of chyme into the small intestine.
Cell theory
States that all living things are composed of cells; cells are the basic functional unit of life; cells arise only from pre-existing cells, and carry their genetic information in the form of DNA.
Hypodermis
Layer of loose connective tissue below the dermis that binds the dermis to the body.
Leukocytes
White blood cells; the component of blood involved in cell defense and immunity. Types include neutrophils, basophils, eosinophils, lymphocytes, and monocytes.
Frameshift 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.
Pancreas
Secreates amylase, trypsin, chymotrypsin, carboxypeptidase, and lipase into the small intestine.
Punctuated equilibrium
A model that holds that evolution is characterized by long periods of stasis punctuated by rapid evolutionary changes.
Pyruvate decarboxylation
The stage of aerobic cellular respiration that comes after glycolysis. Pyruvate is oxidized to acetate, which combines with coenzyme A to form acetyl CoA in the mitochondrial matrix. This process result in the formation of one NADH per pyruvate or two NADH per glucose.
Secondary immune response
Subsequent infections by antigens trigger a more immediate response by the memory cells produced during the primary response.
Osteoblasts
Cells in the bone tissue that secrete organic constituents of the bone matrix.
Substrate
A molecule upon which an enzyme acts.
Centrosome
A region of the cell that contains the centrioles.
Interkinesis
A short rest period between meiosis I and meiosis II. DNA is not replicated.
Prophage
A virus that has integrated its DNA into the host cell’s DNA.
Hepatic portal vein
Carries nutrients absorbed in the small intestine to the liver, where they are modified to enter circulation
Point mutation
Mutation in which one nucleotide base is substituted for another. The protein products are often functional.
Exocytosis
A process in which a vesicle within the cell fuses with the membrane and releases its contents to the extracellular medium.
Threshold value
The minimal value that must be reached in order for a system to respond. Muscle fibers and neurons both exhibit this all-or-none response.
Progesterone
Hormone synthesized and released by the ovaries, corpus luteum, and placenta. During the luteal phase of the menstrual cycle, the corpus luteum secretes it, which, along with estrogen, stimulates the development and maintenance of the endometrial walls for implantation of the embryo.
Superior vena cava
A large vein that returns deoxygenated blood from the head and neck to the right atrium of the heart.
Prophase
The mitotic phase where chromosome condensation and spindle formation occurs. In mesiosis, crossing over occurs here.
Rh factor
An antigen on the surface of erythrocytes, classified as either positive (possessing the factor) or negative (not possessing the factor).
mRNA
Class of RNA that is created from the transcription of DNA (and post-transcriptional processing in eukaryotes).
Somatostatin
Produced and secreted by the delta cells of the pancreas, inhibits the release of glucagon, insulin, and several other hormones throughout the body.
Gluconeogenesis
A process in the liver by which glucose is produced using by-products of glycolysis, lipids, or fats.
Amnion
The innermost extraembryonic membrane that contains amniotic fluid in which the growing fetus is suspended.
Red fibers
Slow-twitch muscle fibers. They are primarily aerobic and contain many mitochondria and myoglobin.
Steroid hormones
Nonpolar hormones that permeate the cell membrane and act by binding to intracellular receptors.
Codon
Nonoverlapping group of three nucleotides. During translation, each is read to determine the next step in protein synthesis, usually by dictating which amino acid is added.
Mesoderm
Primary germ layer that gives rise to the musculoskeletal system, circulatory system, excretory system, gonads, connective tissue, and portions of the digestive and respiratory organs.
Operon
A group of genes or segment of DNA that regulates (bacterial) transcription.
Lysogenic cycle
Phase of viral replication in which the DNA of the bacteriophage becomes integrated in the host’s genome and replicates as the bacteria replicates.
Post-transcriptional RNA processing
In eukaryotes, once an RNA molecule is transcribed, it is spliced and a 5’ cap and 3’ poly-adenine tail are added. This does not occur in prokaryotes.
Portal systems
Circulatory routes in which blood travels through two capillary beds before returning to the heart. Examples are the hepatic, renal, and hypophyseal.
Foramen ovale
A shunt that connects the right atrium to the left atrium in order to bypass the fetal lung.
Nares, pharynx, larynx, trachea, bronchi, bronchioles, alveoli
Sequence the following structures of the respiratory tract: alveoli, trachea, larynx, nares, pharynx, bronchi, bronchioles
Lysosome
Membrane-bound vesicle that contains hydrolytic enzymes used for intracellular digestion.