Microbial Metabolism: Glycolysis, CAC, and Oxidative Phosphorylation

Vocabulary practice flashcards covering microbial metabolism, including redox reactions, glycolysis, the intermediate step (pyruvate oxidation), the Citric Acid Cycle (Krebs cycle), and oxidative phosphorylation (ETC and chemiosmosis).

Oxidation

The loss of one or more electrons ($e^-$) by a molecule or atom during a chemical reaction.

Reduction

The gain of one or more electrons ($e^-$) by a molecule or atom during a chemical reaction.

Redox Reaction

A chemical reaction where an oxidation reaction (loss of electrons) is paired simultaneously with a reduction reaction (gain of electrons).

NADH (Nicotinamide Adenine Dinucleotide, Reduced Form)

A coenzyme and carrier of high-energy electrons that is formed when $NAD^+$ accepts two electrons ($2e^-$) and one proton ($H^+$) during oxidation reactions.

Cellular Respiration

The process by which cells harvest energy ($\text{ATP}$) from nutrients such as glucose through four major pathways: glycolysis, an intermediate step, the Krebs cycle, and oxidative phosphorylation.

Prokaryotic Cellular Respiration Locations

The cellular sites where respiration takes place in prokaryotes: glycolysis, the intermediate step, and the Krebs cycle occur in the cytoplasm, while the electron transport chain is located in the plasma membrane.

Eukaryotic Cellular Respiration Locations

The cellular sites where respiration takes place in eukaryotes: glycolysis occurs in the cytoplasm, the intermediate step and Krebs cycle occur in the mitochondrial matrix, and the electron transport chain resides in the inner mitochondrial membrane.

Glycolysis

A ten-reaction catabolic pathway occurring in the cytoplasm that breaks down one molecule of glucose ($6\text{-carbon}$ sugar) into two molecules of pyruvate ($3\text{-carbon}$ molecules) without directly requiring oxygen, producing a net gain of $2\text{ ATP}$ and $2\text{ NADH}$.

Energy Investment Stage

The initial phase of glycolysis during which $2\text{ ATP}$ molecules are consumed to split a $6\text{-carbon}$ sugar (glucose) into two $3\text{-carbon}$ sugars.

Energy Payoff Stage

The second phase of glycolysis that produces $4\text{ ATP}$ via substrate-level phosphorylation, $2\text{ NADH}$ electron shuttles, and two $3\text{-carbon}$ pyruvate molecules.

Substrate-Level Phosphorylation

The direct synthesis of ATP by transferring a phosphate group directly to ADP, generating $4\text{ ATP}$ during glycolysis and $2\text{ ATP}$ in the Krebs cycle.

Intermediate Step (Pyruvate Oxidation)

The reaction sequence that oxidizes two molecules of pyruvate into two molecules of acetyl-CoA ($2\text{-carbon}$ molecules), producing $2\text{ NADH}$ and releasing $2\text{ CO}_2$ as waste, thereby linking glycolysis to the Citric Acid Cycle.

Krebs Cycle (Citric Acid Cycle)

A series of redox and decarboxylation reactions that oxidizes acetyl-CoA in the mitochondrial matrix (or cytoplasm of prokaryotes), generating $2\text{ ATP}$, $6\text{ NADH}$, $2\text{ FADH}_2$, and $4\text{ CO}_2$ per glucose molecule.

Electron Transport Chain (ETC)

A series of membrane-associated electron carrier molecules that participate in redox reactions, receiving electrons from NADH and $FADH_2$ to pump protons ($H^+$) across the membrane and generate a proton motive force.

Chemiosmosis

The movement of hydrogen ions (protons, $H^+$) down their concentration gradient across a membrane through ATP synthase to supply the energy needed to make ATP from ADP and phosphate ($P_i$).

ATP Synthase

A membrane enzyme complex that captures the energy of protons flowing down their electrochemical gradient from high to low concentration to recharge ADP and phosphate into ATP.

Oxidative Phosphorylation

The metabolic process combining the electron transport chain and chemiosmosis that utilizes the energy released by electron transfer and a proton gradient to generate up to $34\text{ ATP}$.

Final Electron Acceptor

Molecular oxygen ($O_2$) in aerobic respiration, which combines with electrons and protons ($H^+$) at the end of the electron transport chain to form water ($H_2O$).

Proton Motive Force

The electrochemical concentration gradient of protons ($H^+$) created across the membrane by the proton pumps of the electron transport chain, used to power chemiosmosis.

Overall Chemical Equation for Aerobic Cellular Respiration

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + 38\text{ ATP}$, representing the theoretical maximum production of $38\text{ ATP}$ from one molecule of glucose.