Lecture Vocabulary: Enzymes, Metabolism, and Cellular Respiration

Vocabulary flashcards covering key terms and concepts from enzyme structure/function and carbohydrate metabolism, including glycolysis, TCA cycle, ETC, and respiration.

Primary structure

The linear sequence of amino acids in a protein that determines its higher-level structures.

Secondary structure

Local folding patterns (e.g., alpha helices, beta sheets) stabilized by hydrogen bonds.

Tertiary structure

The three-dimensional shape of a single polypeptide arising from folding and side-chain interactions.

Quaternary structure

The assembly of multiple polypeptide subunits into a functional protein.

Enzyme

A biological catalyst that speeds up chemical reactions by lowering activation energy at physiological temperatures.

Active site

The binding pocket of an enzyme where substrates bind and the reaction occurs.

Substrate

The molecule(s) acted upon by an enzyme, becoming transformed during the reaction.

Coenzyme

An organic non-protein molecule (e.g., NADPH, NADP+, ATP) that participates in enzyme reactions.

Cofactor

An inorganic ion (e.g., Cu2+, Zn2+) that assists enzyme activity by stabilizing substrates or catalysis.

Activation energy

The energy input required to start a reaction; enzymes lower this value.

Specificity

Enzymes recognize and act on specific substrates due to the shape and chemistry of the active site.

Enzyme–substrate complex

The temporary complex formed when a substrate binds the enzyme’s active site.

Reusable enzyme

Enzymes are not consumed in reactions and can catalyze many cycles.

Denaturation

Loss of protein structure and function due to factors like heat or extreme pH.

pH optimum

The pH at which an enzyme has maximal activity; deviations reduce activity.

Protonation

Addition of protons to a molecule, altering charge and potentially protein shape.

Deprotonization

Removal of protons from a molecule, altering charge and potentially protein shape.

Competitive inhibitor

A molecule that binds the active site, blocking substrate binding and slowing the reaction.

Allosteric inhibitor

An inhibitor that binds at a site away from the active site and distorts the active site.

Feedback inhibition

End product inhibits an early enzyme in a pathway to regulate production.

Metabolic pathway

A series of enzyme-catalyzed steps converting a substrate to a product with potential regulation.

End product

The final product of a pathway, which can feedback to regulate its production.

Glycolysis

Cytoplasmic pathway converting glucose to pyruvate, with energy investment and payoff phases, yielding net 2 ATP and NADH per glucose.

Pyruvate oxidation

Conversion of pyruvate to acetyl-CoA, releasing CO2 and generating NADH; links glycolysis to the TCA cycle.

Acetyl-CoA

Two-carbon acetyl group bound to CoA; substrate that enters the TCA cycle.

TCA cycle (Krebs, citric acid cycle)

Oxidizes acetyl-CoA to CO2, producing NADH, FADH2, and ATP/GTP.

CO2

Carbon dioxide produced during pyruvate oxidation and the TCA cycle; exhaled as waste.

NAD+/NADH

Electron carrier; NAD+ accepts electrons to become NADH (oxidized to reduced form).

FAD/FADH2

Flavin adenine dinucleotide; accepts electrons to become FADH2 in the TCA cycle.

Electron Transport Chain (ETC)

Membrane-bound proteins that transfer electrons, pump protons, and create a proton gradient to drive ATP synthesis.

Proton motive force

Proton gradient across a membrane that powers ATP synthesis via ATP synthase.

ATP synthase

Enzyme that uses the proton gradient to phosphorylate ADP to ATP.

Oxygen as terminal electron acceptor

In aerobic respiration, oxygen accepts electrons at the end of the ETC to form water.

Cyanide poisoning

Cyanide blocks electron transfer to oxygen, halting ATP production and energy metabolism.