Bioenergetics, Cellular Respiration, and Fermentation

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

Energy

Capacity to do work or cause change; required by cells for growth, repair, and reproduction.

First Law of Thermodynamics

Energy cannot be created or destroyed, only converted from one form to another.

Second Law of Thermodynamics

Every energy conversion loses usable energy as heat; no conversion is 100 % efficient.

ATP (Adenosine Triphosphate)

Immediate, usable energy currency of the cell; energy stored in its terminal phosphate bond.

Metabolism

Sum of all biochemical reactions in a cell, including catabolism and anabolism.

Catabolic Reactions

Breaking-down (degradative) reactions that release energy, often via oxidation and hydrolysis.

Anabolic Reactions

Building-up (synthetic) reactions that require energy, often via reduction and dehydration synthesis.

Oxidation

Loss of electrons or hydrogen atoms from a molecule.

Reduction

Gain of electrons or hydrogen atoms by a molecule.

Hydrolysis

Catabolic reaction that splits molecules by adding water.

Dehydration Synthesis

Anabolic reaction that forms bonds by removing water.

Enzyme

Protein catalyst that speeds up reactions by lowering activation energy without being consumed.

Active Site

Region on an enzyme where the substrate binds and reaction occurs.

Activation Energy

Minimum energy required to start a chemical reaction; lowered by enzymes.

Substrate

Reactant molecule upon which an enzyme acts.

Enzyme-Substrate Complex

Temporary molecule formed when enzyme binds its substrate at the active site.

Substrate Saturation

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

Denaturation

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

Optimal Temperature (Enzymes)

Temperature at which an enzyme’s activity is at its maximum before denaturation occurs.

Optimal pH (Enzymes)

Specific pH range where an enzyme functions best (e.g., pepsin in acid, trypsin near pH 7).

Coenzyme

Organic molecule (often vitamin-derived) that assists enzymes in redox reactions.

NAD+

Oxidized coenzyme that can accept electrons/hydrogen to become NADH.

NADH

Reduced form of NAD+; high-energy electron carrier delivering electrons to ETC.

FAD

Oxidized coenzyme that becomes FADH₂ after gaining electrons/hydrogen.

FADH₂

Reduced form of FAD; electron carrier entering the ETC at complex II.

Cellular Respiration

Process of converting energy in food molecules to ATP; includes glycolysis, transition, Krebs, and ETC.

Glycolysis

Anaerobic splitting of glucose into two pyruvate, yielding 2 ATP and 2 NADH in cytoplasm.

Transition Reaction

Conversion of pyruvate to acetyl-CoA plus CO₂ and NADH inside mitochondria; requires oxygen.

Acetyl-CoA

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

Krebs Cycle (Citric Acid Cycle)

Mitochondrial cycle that oxidizes acetyl-CoA, producing 2 ATP, 6 NADH, 2 FADH₂, and 4 CO₂ per glucose.

Electron Transport Chain (ETC)

Series of membrane proteins that pass electrons, pump H⁺, and drive ATP synthesis.

ATP Synthase

Mitochondrial enzyme that uses proton gradient to phosphorylate ADP → ATP (oxidative phosphorylation).

Aerobic Respiration

Complete oxidation of glucose with oxygen, yielding up to 38 ATP, CO₂, and H₂O.

Anaerobic Respiration

Energy production without oxygen, relying on glycolysis and fermentation; yields 2 ATP per glucose.

Fermentation

Pathway that regenerates NAD+ from NADH when ETC stops; produces lactic acid or ethanol + CO₂.

Lactic Acid Fermentation

Human anaerobic process converting pyruvate to lactate, freeing NAD+ for glycolysis.

Alcoholic Fermentation

Yeast process converting pyruvate to ethanol and CO₂, regenerating NAD+.

Oxidative Phosphorylation

ATP formation powered by electron transport and chemiosmotic proton gradient.

Oxygen (Terminal Electron Acceptor)

Final acceptor of electrons in ETC, forming water; absence stops ETC.

Pyruvate

Three-carbon end product of glycolysis; precursor for acetyl-CoA or fermentation.

Glucose Catabolism

Overall breakdown of glucose to CO₂, H₂O, and ATP through glycolysis, Krebs, and ETC.

38 ATP Yield

Theoretical maximum ATP produced per glucose in prokaryotes; ~36 ATP in eukaryotes.

Fatty Acid Catabolism

β-oxidation of fats into acetyl-CoA units that enter Krebs cycle for ATP production.

Protein Catabolism

Removal of amino groups and entry of carbon skeletons into glycolysis or Krebs for energy.

Oxygen Debt

Post-exercise demand for oxygen to clear lactate and restore aerobic conditions.