Comprehensive MCAT Biology & Biochemistry Review

Vocabulary flashcards covering key structures, processes, and definitions from multiple MCAT biology and biochemistry chapters, designed for comprehensive exam review.

What is the Nucleus?

The Nucleus is a membrane-bound organelle that houses genetic material required for replication and transcription in eukaryotic cells.

What is the Nuclear Envelope?

The Nuclear Envelope is a double membrane surrounding the nucleus that separates nuclear contents from the cytoplasm.

What are Histones?

Histones are positively charged proteins around which DNA winds to form nucleosomes; they help organize and condense DNA.

What is a Chromosome?

A Chromosome is a highly condensed structure of DNA and histone proteins formed during cell division.

What is the Nucleolus?

The Nucleolus is a dense region within the nucleus where ribosomal RNA (rRNA) is synthesized.

What is a Mitochondrion?

A Mitochondrion is a semi-autonomous organelle with inner and outer membranes that generates ATP by oxidative phosphorylation and can trigger apoptosis.

What are Cristae?

Cristae are infoldings of the mitochondrial inner membrane that increase surface area for the electron-transport chain.

What is Apoptosis?

Apoptosis is programmed cell death, which in mitochondria is initiated by release of ETC enzymes into the cytosol.

What is a Lysosome?

A Lysosome is a membrane-bound vesicle containing hydrolytic enzymes that digest cellular waste, macromolecules, and pathogens.

What is Autolysis?

Autolysis is the self-destruction of a cell via lysosomal enzyme release.

What is the Rough Endoplasmic Reticulum (RER)?

The Rough Endoplasmic Reticulum (RER) is ER studded with ribosomes; it synthesizes proteins destined for secretion or membrane insertion.

What is the Smooth Endoplasmic Reticulum (SER)?

The Smooth Endoplasmic Reticulum (SER) lacks ribosomes; it functions in lipid synthesis, detoxification, and shuttling proteins from RER to Golgi.

What is the Golgi Apparatus?

The Golgi Apparatus is a stack of membrane-bound sacs that modifies, sorts, and packages proteins and lipids for delivery.

What is Exocytosis?

Exocytosis is the process by which a vesicle fuses with the plasma membrane to release its contents outside the cell.

What is a Peroxisome?

A Peroxisome is an organelle containing hydrogen peroxide; it breaks down very long-chain fatty acids via β-oxidation and participates in phospholipid synthesis.

What is the Cytoskeleton?

The Cytoskeleton is a network of protein fibers (microfilaments, microtubules, intermediate filaments) that provides cell shape, support, and intracellular transport pathways.

What is a Microfilament?

A Microfilament is a solid rod of actin; it resists compression, enables movement with myosin, and forms the contractile ring in cytokinesis.

What is a Microtubule?

A Microtubule is a hollow polymer of tubulin providing tracks for motor proteins and forming structures such as cilia, flagella, and the mitotic spindle.

What are Cilia?

Cilia are microtubule-based projections that move fluid along the cell surface, e.g., in the respiratory tract.

What is a Flagellum (Eukaryotic)?

A Flagellum (Eukaryotic) is a microtubule-based whip-like structure enabling cell motility (9+2 arrangement).

What is the 9 + 2 Structure?

The 9 + 2 Structure is an arrangement of nine doublet microtubules surrounding two central singlets in eukaryotic motile cilia and flagella.

What are Centrioles?

Centrioles are cylindrical microtubule organizing centers located in centrosomes; they form the mitotic spindle and attach to kinetochores.

What is Epithelial Tissue?

Epithelial Tissue consists of sheets of cells covering body surfaces, lining cavities, and forming the functional (parenchymal) part of many organs.

What is the Basement Membrane?

The Basement Membrane is a layer of connective tissue anchoring epithelial cells to underlying structures.

What is the Parenchyma?

The Parenchyma refers to the functional parts of an organ, usually composed of epithelial cells (e.g., nephrons, hepatocytes).

What is Stroma?

Stroma is the supportive connective tissue framework of an organ.

What is Simple Epithelium?

Simple Epithelium is a single layer of epithelial cells.

What is Stratified Epithelium?

Stratified Epithelium consists of multiple layers of epithelial cells providing protection.

What is Pseudostratified Epithelium?

Pseudostratified Epithelium is a single layer of cells with varying heights that appear multilayered.

What are Cuboidal Cells?

Cuboidal Cells are cube-shaped epithelial cells specialized for secretion.

What are Columnar Cells?

Columnar Cells are tall, slender epithelial cells specialized for absorption or secretion.

What are Squamous Cells?

Squamous Cells are flat, scale-like epithelial cells allowing diffusion.

What are Archaea?

Archaea are single-celled prokaryotes visually resembling bacteria but genetically/metabolically closer to eukaryotes; often extremophiles.

What is a Bacterium?

A Bacterium is a single-celled prokaryote with a cell wall, plasma membrane, and often flagella or fimbriae.

What is a Coccus?

Coccus refers to a spherical bacterial shape.

What is a Bacillus?

Bacillus refers to a rod-shaped bacterium.

What is a Spirillum?

Spirillum refers to a spiral-shaped bacterium.

What is an Obligate Aerobe?

An Obligate Aerobe is a bacterium that requires oxygen for metabolism.

What is an Obligate Anaerobe?

An Obligate Anaerobe is a bacterium that is poisoned by oxygen.

What is a Facultative Anaerobe?

A Facultative Anaerobe is a bacterium that can switch between aerobic and anaerobic metabolism.

What is a Gram-Positive Cell Wall?

A Gram-Positive Cell Wall has a thick peptidoglycan layer containing lipoteichoic acid; it stains purple with Gram stain.

What is a Gram-Negative Cell Wall?

A Gram-Negative Cell Wall has a thin peptidoglycan layer plus an outer membrane with lipopolysaccharides; it stains pink and elicits a strong immune response.

What is the Cell Envelope (Bacteria)?

The Cell Envelope (Bacteria) is the combined structure of the cell wall and plasma membrane in bacteria.

What is Chemotaxis?

Chemotaxis is a directed cell movement toward or away from chemical stimuli; used by bacteria with flagella.

What is a Plasmid?

A Plasmid is a small, extrachromosomal DNA molecule that may confer advantages such as antibiotic resistance.

What is an Episome?

An Episome is a plasmid capable of integrating into the bacterial genome.

What is Transformation (Bacteria)?

Transformation (Bacteria) is a genetic recombination process where bacteria uptake free DNA from the environment.

What is Conjugation?

Conjugation is bacterial 'mating' involving the transfer of DNA through a sex pilus from an F⁺ donor to an F⁻ recipient.

What is the F Fertility Factor?

The F Fertility Factor is a plasmid encoding sex pilus genes; it confers donor ability in conjugation.

What is Transduction?

Transduction is gene transfer in bacteria via a bacteriophage vector.

What is a Transposon?

A Transposon is a mobile genetic element that can move within the genome, causing insertions or deletions.

What is the Lag Phase?

The Lag Phase is the initial period of bacterial growth where cells adapt to a new environment.

What is the Exponential (Log) Phase?

The Exponential (Log) Phase is rapid bacterial population growth once adaptation is complete.

What is the Stationary Phase?

The Stationary Phase is when growth slows as resources become limited; population size plateaus.

What is the Death Phase?

The Death Phase is when the bacterial population declines as resources are depleted.

What is a Virus?

A Virus is an obligate intracellular parasite consisting of genetic material in a protein coat, sometimes surrounded by an envelope.

What is a Capsid?

A Capsid is the protein coat surrounding a viral genome.

What is a Virion?

A Virion is an individual viral particle capable of infecting cells.

What is a Bacteriophage?

A Bacteriophage is a virus that infects bacteria; it injects genetic material via a tail sheath and tail fibers.

What is a Positive-Sense RNA Virus?

A Positive-Sense RNA Virus has a single-stranded RNA genome that can be directly translated by host ribosomes.

What is a Negative-Sense RNA Virus?

A Negative-Sense RNA Virus has a single-stranded RNA genome complementary to mRNA; it requires RNA replicase to synthesize a template strand.

What is a Retrovirus?

A Retrovirus is an enveloped RNA virus using reverse transcriptase to integrate a DNA copy into the host genome.

What is the Lytic Cycle?

The Lytic Cycle is a viral life cycle leading to host cell lysis and release of progeny; the phage is considered virulent.

What is the Lysogenic Cycle?

The Lysogenic Cycle is where the phage genome integrates as a prophage; it replicates with the host until stress induces a lytic switch.

What is a Prion?

A Prion is an infectious protein causing misfolding of other proteins, often by converting α-helix to β-sheet.

What is a Viroid?

A Viroid is a small circular RNA pathogen that silences plant gene expression; few infect humans.

What is Interphase?

Interphase is the portion of the cell cycle including G₁, S, and G₂ phases; the cell grows and replicates DNA.

What is Cyclin-Dependent Kinase (CDK)?

Cyclin-Dependent Kinase (CDK) is a kinase activated by cyclins; it phosphorylates transcription factors to drive cell-cycle progression.

What is p53?

p53 is a tumor-suppressor protein controlling cell-cycle checkpoints; its loss leads to cancer.

What is Crossing Over?

Crossing Over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis; it increases genetic diversity.

What is Independent Assortment?

Independent Assortment is a Mendelian principle that allele segregation of one gene is independent of another, due to random orientation of homologs in metaphase I.

What are Seminiferous Tubules?

Seminiferous Tubules are the site of spermatogenesis within the testes; they contain Sertoli cells that nourish developing sperm.

What are Leydig (Interstitial) Cells?

Leydig (Interstitial) Cells are testicular cells stimulated by LH to secrete testosterone.

What is Oogenesis?

Oogenesis is the production of female gametes; primary oocytes are arrested in prophase I until ovulation.

What is the Zona Pellucida?

The Zona Pellucida is a glycoprotein layer surrounding the oocyte; it is required for sperm binding and acrosome reaction.

What is the Corpus Luteum?

The Corpus Luteum is a ruptured follicle after ovulation that secretes progesterone under LH stimulation.

What is Human Chorionic Gonadotropin (hCG)?

Human Chorionic Gonadotropin (hCG) is a placental hormone that maintains the corpus luteum in early pregnancy.

What is a Blastocyst?

A Blastocyst is a mammalian blastula with a trophoblast (future placenta) and inner cell mass (future embryo).

What is Gastrulation?

Gastrulation is the developmental process forming the three germ layers: ectoderm, mesoderm, and endoderm.

What is Neurulation?

Neurulation is the formation of the neural tube from ectoderm under the inductive influence of the notochord.

What is a Totipotent Cell?

A Totipotent Cell is a stem cell capable of differentiating into any embryonic or extra-embryonic tissue.

What is a Pluripotent Cell?

A Pluripotent Cell is a stem cell able to differentiate into any cell type of the three germ layers, but not extra-embryonic tissues.

What is a Morphogen?

A Morphogen is a signaling molecule that diffuses through tissues, forming a concentration gradient to dictate cell fate.

What is the Foramen Ovale?

The Foramen Ovale is a fetal shunt that directs blood from the right atrium to the left atrium, bypassing fetal lungs.

What is the Ductus Arteriosus?

The Ductus Arteriosus is a fetal vessel connecting the pulmonary artery to the aorta to bypass the lungs.

What is Resting Membrane Potential?

Resting Membrane Potential is the electrical potential difference (\approx -70 mV) across a neuronal membrane maintained by Na⁺/K⁺ ATPase and leak channels.

What is Saltatory Conduction?

Saltatory Conduction is the jumping propagation of action potentials along myelinated axons at nodes of Ranvier.

What is the Absolute Refractory Period?

The Absolute Refractory Period is the time during which another action potential cannot be initiated, regardless of stimulus strength.

What is Neurotransmitter Reuptake?

Neurotransmitter Reuptake is the transport of a neurotransmitter from the synaptic cleft back into the presynaptic neuron, terminating the signal.

What is the Somatic Nervous System?

The Somatic Nervous System is a division of the PNS controlling voluntary skeletal muscle movement; it involves a single efferent neuron.

What is the Autonomic Nervous System?

The Autonomic Nervous System is the involuntary division of the PNS controlling smooth muscle, cardiac muscle, and glands; it uses a two-neuron chain.

What is the Parasympathetic Nervous System?

The Parasympathetic Nervous System is a branch of the autonomic system that conserves energy; rest-and-digest responses are mediated by acetylcholine.

What is the Sympathetic Nervous System?

The Sympathetic Nervous System is a branch of the autonomic system activating fight-or-flight responses; it releases norepinephrine and epinephrine.

What is a Peptide Hormone?

A Peptide Hormone is a hydrophilic hormone derived from amino acids; it binds cell-surface receptors and acts via second messengers.

What is a Steroid Hormone?

A Steroid Hormone is a lipophilic hormone derived from cholesterol; it binds intracellular receptors to regulate gene transcription.

What is an Amino-Acid Derivative Hormone?

An Amino-Acid Derivative Hormone is a hormone synthesized from one or two amino acids, e.g., thyroid hormones, catecholamines; receptor location varies.

What is a Tropic Hormone?

A Tropic Hormone is a hormone that triggers the release of another hormone (e.g., ACTH, TSH).

What is Growth Hormone (GH)?

Growth Hormone (GH) is an anterior pituitary hormone that promotes bone and muscle growth and elevates blood glucose.

What is Antidiuretic Hormone (ADH)?

Antidiuretic Hormone (ADH) is a posterior pituitary peptide increasing water reabsorption in collecting ducts; it raises blood pressure.

What is Calcitonin?

Calcitonin is a thyroid C-cell hormone that lowers plasma calcium by increasing excretion, decreasing gut absorption, and promoting bone uptake.