Bioenergetics, Cellular Respiration, and Fermentation

Vocabulary flashcards covering key terms and definitions from the lecture on bioenergetics, cellular respiration, and fermentation.

Energy (biological definition)

The capacity to do work or bring about change within cells.

Mechanical Energy

Energy of movement, such as muscle contraction or cytoplasmic streaming.

Chemical Energy

Energy stored in molecular bonds, e.g., those in food molecules like glucose.

First Law of Thermodynamics

Energy cannot be created or destroyed; it can only change forms.

Second Law of Thermodynamics

Energy conversions are never 100% efficient—some useful energy is lost as heat.

ATP (Adenosine Triphosphate)

The cell’s immediate, directly usable energy currency.

High-Energy Phosphate Bond

The terminal phosphate-phosphate bond in ATP that stores/release energy.

Metabolism

All biochemical reactions occurring within a cell.

Catabolism

Metabolic pathways that break down molecules, releasing energy (often via oxidation).

Anabolism

Metabolic pathways that build molecules, consuming energy (often via reduction).

Oxidation

Loss of electrons or hydrogen atoms from a molecule.

Reduction

Gain of electrons or hydrogen atoms by a molecule.

Hydrolysis Reaction

Catabolic reaction in which water splits bonds, e.g., ATP → ADP + Pi.

Dehydration Synthesis

Anabolic reaction that forms bonds by removing water.

Enzyme

A (usually) protein catalyst that speeds up specific biochemical reactions.

Active Site

The region of an enzyme where substrate binding and catalysis occur.

Activation Energy

Energy input required to start a chemical reaction.

Enzyme Saturation

Point at which all active sites are occupied and reaction rate plateaus.

Enzyme Denaturation

Loss of an enzyme’s 3-D shape (and function) due to extreme heat or pH.

Optimal Temperature (enzyme)

Temperature at which an enzyme’s activity is maximal before denaturation.

Optimal pH (enzyme)

pH value at which an enzyme functions best (e.g., pepsin ~pH 2).

Coenzyme

Non-protein molecule (often vitamin-derived) that assists enzymes; e.g., NAD⁺, FAD.

NAD⁺

Oxidized coenzyme that accepts electrons/H to become NADH.

NADH

Reduced, high-energy electron carrier form of NAD⁺.

FAD

Oxidized coenzyme that accepts electrons/H to become FADH₂.

FADH₂

Reduced, high-energy electron carrier form of FAD.

Aerobic Cellular Respiration

Glucose breakdown with oxygen, yielding CO₂, H₂O, and up to 38 ATP.

Anaerobic Respiration (Fermentation)

Energy extraction from glucose without oxygen, producing 2 ATP and organic by-products.

Glycolysis

Cytoplasmic pathway that splits glucose into 2 pyruvate, producing 2 ATP and 2 NADH; oxygen not required.

Transition Reaction

Conversion of 2 pyruvate to 2 acetyl-CoA, generating 2 NADH and 2 CO₂ in mitochondria (requires O₂).

Acetyl-CoA

Two-carbon molecule that enters the Krebs cycle after combining with oxaloacetate.

Krebs Cycle (Citric Acid Cycle)

Mitochondrial cycle producing 2 ATP, 6 NADH, 2 FADH₂, and 4 CO₂ per glucose.

Electron Transport Chain (ETC)

Series of inner-mitochondrial membrane proteins that transfer electrons to O₂ and pump H⁺.

ATP Synthase

Membrane enzyme that uses H⁺ gradient to phosphorylate ADP to ATP (oxidative phosphorylation).

Oxygen (cellular respiration)

Final electron acceptor in the ETC, forming water.

Oxidative Phosphorylation

ATP production coupled to electron transport and H⁺ gradient in mitochondria.

Max ATP Yield per Glucose

Up to 38 ATP (2 glycolysis, 2 Krebs, ~34 ETC).

Lactic Acid Fermentation

Human anaerobic pathway converting pyruvate to lactate and regenerating NAD⁺.

Alcohol Fermentation

Yeast anaerobic pathway converting pyruvate to ethanol and CO₂ while regenerating NAD⁺.

Fatty Acid Catabolism

β-oxidation of fats to acetyl-CoA for Krebs cycle entry.

Protein Catabolism

Deamination of amino acids followed by entry of carbon skeletons into glycolysis or Krebs.