MCAT Biology/Biochem Set

MCAT biology

Macromolecule

A large polymer built from repeating monomer subunits.

Monomer

A small molecule that can join with others to form a polymer.

Polymerase

Enzyme that catalyzes polymerization of monomers into polymers.

Polymerization

The chemical process of linking monomers to form a polymer.

Protein

A biological macromolecule composed of amino acids linked by peptide bonds.

Amino Acid

The monomeric building block of proteins; contains an amine, carboxyl, and variable side chain.

N-C-C Backbone

The repeating nitrogen-carbon-carbon structure common to all amino acids in a peptide chain.

Peptide Bond

Covalent linkage between amino acids formed by dehydration synthesis.

Dehydration Synthesis

Reaction that joins two molecules by removing water.

Hydrolysis

Reaction that splits molecules by the addition of water.

Primary Structure (Protein)

The linear sequence of amino acids in a polypeptide chain.

Secondary Structure (Protein)

Local folding into α-helices or β-sheets stabilized by hydrogen bonds.

α-Helix

Right-handed coil secondary structure of proteins.

β-Sheet

Extended, sheet-like secondary structure of proteins.

Tertiary Structure (Protein)

Three-dimensional folding of a polypeptide driven by side-chain interactions.

Quaternary Structure (Protein)

Assembly of multiple polypeptide subunits into a functional complex.

Disulfide Bridge

Covalent bond between two cysteine residues stabilizing protein structure.

Hydrophobic Effect

Tendency of non-polar residues to cluster away from water in proteins.

Carbohydrate

Macromolecule composed of sugar monomers; source of energy and structure.

Monosaccharide

Single sugar molecule such as glucose, fructose, or galactose.

Disaccharide

Carbohydrate composed of two monosaccharides linked by glycosidic bond.

Polysaccharide

Long chain carbohydrate formed by many monosaccharides.

Glucose

Six-carbon aldose sugar; primary cellular energy source.

Fructose

Six-carbon ketose sugar found in fruit.

Galactose

Monosaccharide structurally similar to glucose; component of lactose.

Ribose

Five-carbon sugar in RNA.

Deoxyribose

Five-carbon sugar lacking one oxygen; found in DNA.

Maltose

Disaccharide of two glucose units.

Sucrose

Table sugar composed of glucose and fructose.

Lactose

Milk sugar composed of glucose and galactose.

Glycogen

Highly branched glucose storage polysaccharide in animals.

Starch

Glucose storage polysaccharide in plants.

Cellulose

Structural polysaccharide in plant cell walls.

Lipid

Hydrophobic biomolecule including fats, oils, and cholesterol.

Fatty Acid

Long hydrocarbon chain with terminal carboxylic acid.

Saturated Fat

Fatty acid with no carbon-carbon double bonds; solid at room temperature.

Unsaturated Fat

Fatty acid with at least one double bond; liquid at room temperature.

Triglyceride

Ester of glycerol with three fatty acids; storage fat.

Phospholipid

Glycerol, two fatty acids, and phosphate-containing head; forms lipid bilayers.

Amphipathic

Having both hydrophilic and hydrophobic regions.

Lipid Bilayer

Double-layered arrangement of phospholipids in membranes.

Terpene

Lipid built from isoprene units; basis of waxes and certain vitamins.

Isoprene

Five-carbon building block of terpenes.

Cholesterol

Steroid lipid with 3 six-carbon and 1 five-carbon rings; membrane component.

Steroid Hormone

Cholesterol-derived signaling molecule such as testosterone or estrogen.

Gibbs Free Energy (G)

Energy available to do work in a system.

Enthalpy (H)

Heat content or potential energy of a system.

Entropy (S)

Measure of disorder or randomness in a system.

Exergonic

Reaction with negative ΔG; releases energy; spontaneous.

Endergonic

Reaction with positive ΔG; requires energy input; non-spontaneous.

Reaction Coupling

Using a favorable reaction (e.g., ATP hydrolysis) to drive an unfavorable one.

ATP

Adenosine triphosphate; universal cellular energy currency.

Activation Energy (Ea)

Minimum energy required to initiate a chemical reaction.

Transition State

High-energy, unstable state during a reaction.

Catalyst

Substance that increases reaction rate without being consumed.

Enzyme

Protein catalyst that accelerates biochemical reactions.

Active Site

Region on enzyme where substrate binds and reaction occurs.

Allosteric Site

Regulatory site on enzyme distinct from active site.

Lock-and-Key Model

Enzyme theory where active site fits substrate exactly.

Induced-Fit Model

Enzyme theory where active site molds around substrate.

Feedback Inhibition

Product of pathway inhibits an earlier step to regulate flux.

Vmax

Maximum reaction velocity when enzyme is saturated with substrate.

Km

Substrate concentration at which reaction rate is half Vmax.

Competitive Inhibitor

Molecule that competes with substrate for active site; raises Km.

Non-competitive Inhibitor

Binds allosterically; lowers Vmax without changing Km.

Uncompetitive Inhibitor

Binds only to enzyme-substrate complex; lowers both Km and Vmax.

Mixed Inhibitor

Binds enzyme with or without substrate; lowers Vmax, Km variable.

Lineweaver-Burk Plot

Double-reciprocal graph of enzyme kinetics.

Oxidation

Loss of electrons, hydrogen, or gain of oxygen.

Reduction

Gain of electrons, hydrogen, or loss of oxygen.

Redox Reaction

Chemical reaction involving electron transfer.

Cellular Respiration

Process that converts glucose and O₂ to CO₂, H₂O, and ATP.

Glycolysis

Anaerobic breakdown of glucose into pyruvate; occurs in cytoplasm.

Pyruvate

Three-carbon end product of glycolysis.

Pyruvate Dehydrogenase Complex (PDC)

Enzyme converting pyruvate to acetyl-CoA in mitochondrial matrix.

Acetyl-CoA

Two-carbon molecule entering Krebs cycle.

Krebs Cycle

Citric acid cycle oxidizing acetyl-CoA to CO₂; produces NADH/FADH₂.

Oxidative Phosphorylation

Coupling of electron transport to ATP synthesis via ATP synthase.

Electron Transport Chain (ETC)

Series of membrane proteins that transfer electrons and pump protons.

NADH

Reduced electron carrier that donates electrons to ETC.

FADH₂

Reduced flavin carrier donating electrons to ETC.

Proton Gradient

H⁺ concentration difference across membrane used to make ATP.

ATP Synthase

Membrane enzyme that synthesizes ATP using proton motive force.

Fermentation

Anaerobic process regenerating NAD⁺ from NADH; forms lactate or ethanol.

Gluconeogenesis

Formation of glucose from non-carbohydrate precursors like pyruvate.

Glycogenesis

Synthesis of glycogen from glucose for storage.

Glycogenolysis

Breakdown of glycogen to release glucose.

Pentose Phosphate Pathway (PPP)

Metabolic pathway producing NADPH and ribose-5-phosphate.

NADPH

Electron carrier used in reductive biosynthesis and antioxidant defense.

Beta-Oxidation

Catabolic removal of two-carbon units from fatty acids to form acetyl-CoA.

Fatty Acid Synthesis

Anabolic process building fatty acids from acetyl-CoA and malonyl-CoA.

Ketogenesis

Formation of ketone bodies from acetyl-CoA during starvation.

Protease

Enzyme that hydrolyzes peptide bonds in proteins.

Metabolism

All chemical reactions involved in maintaining life.

Nucleotide

Monomer of nucleic acids composed of sugar, phosphate, and base.

Purine

Two-ring nitrogenous base: adenine or guanine.

Pyrimidine

Single-ring base: cytosine, thymine, or uracil.

Phosphodiester Bond

Covalent linkage between nucleotides in DNA/RNA backbone.

Antiparallel

Orientation of DNA strands running 5′→3′ opposite each other.

Complementary Base Pairing

Specific hydrogen bonding of A-T (or A-U) and C-G.