Biol 110: Cellular Respiration, Fermentation, and Metabolic Pathways

Vocabulary practice flashcards covering aerobic respiration stages (glycolysis, pyruvate oxidation, Krebs cycle, electron transport chain, chemiosmosis), net ATP bookkeeping, anaerobic respiration, fermentation, and metabolic fuel switching.

Aerobic Respiration

A cellular process that breaks down glucose ($C_6H_{12}O_6$) across four stages in the presence of oxygen ($O_2$), which acts as the final electron acceptor to form water ($H_2O$) and generate a net yield of $36\text{ to }38\,\text{ATP}$.

Glycolysis

An ancient metabolic process occurring continuously in the cytosol outside the mitochondria, operating with or without oxygen to split one $6\text{-carbon}$ glucose molecule into two $3\text{-carbon}$ pyruvate molecules.

Energy Investment Phase

The beginning phase of glycolysis in which $2\,\text{ATP}$ are consumed to attach two phosphate groups to glucose, creating molecular stress and destabilizing it so it can be cleaved in half.

Energy Harvest Phase

The second phase of glycolysis that yields a gross amount of $4\,\text{ATP}$ and $2\,\text{NADH}$, resulting in a net yield of $2\,\text{ATP}$ and $2\,\text{NADH}$ per glucose after repaying the initial investment.

$\text{NAD}^+$ and $\text{NADH}$

High-energy electron carriers; $\text{NAD}^+$ is the oxidized state, while $\text{NADH}$ is the reduced state carrying two high-energy electrons that can yield up to $3\,\text{ATP}$ in the electron transport chain.

Pyruvate

The three-carbon end-product molecule of glycolysis; two pyruvate molecules are produced per glucose molecule and undergo subsequent processing in the mitochondria.

Pyruvate Oxidation

The second stage of cellular respiration occurring as pyruvate enters the mitochondrial matrix, where each $3\text{-carbon}$ pyruvate is broken down into a $2\text{-carbon}$ acetyl group, releasing $CO_2$ and producing $\text{NADH}$.

Pyruvate Dehydrogenase

The eukaryotic enzyme responsible for removing a molecule of $CO_2$ from pyruvate and attaching the resulting two-carbon acetyl fragment to coenzyme A.

Acetyl CoA

A compound formed by linking a $2\text{-carbon}$ acetyl group to coenzyme A, functioning as a molecular carrier to deliver the acetyl group into the citric acid cycle.

Mitochondrial Matrix

The innermost compartment at the center of the mitochondrion where pyruvate oxidation and the citric acid cycle take place.

Citric Acid Cycle (Krebs Cycle)

A cyclic pathway in the mitochondrial matrix that processes acetyl groups; each single turn produces $1\,\text{ATP}$, $3\,\text{NADH}$, and $1\,\text{FADH}_2$, doubling to $2\,\text{ATP}$, $6\,\text{NADH}$, and $2\,\text{FADH}_2$ per glucose molecule across two turns.

Oxaloacetate

A $4\text{-carbon}$ starting molecule in the Krebs cycle that binds to a $2\text{-carbon}$ acetyl group to form citric acid, and is regenerated at the completion of each turn.

$\text{FAD}$ and $\text{FADH}_2$

An electron carrier pair utilized in the Krebs cycle; $\text{FAD}$ is the oxidized form and $\text{FADH}_2$ is the reduced form that delivers electrons to CoQ10, yielding approximately $2\,\text{ATP}$.

Electron Transport Chain

A series of protein complexes located in the inner mitochondrial membrane that sequentially transfer electrons from $\text{NADH}$ and $\text{FADH}_2$ to oxygen, utilizing the liberated energy to pump protons into the intermembrane space.

CoQ10

A specialized electron carrier located at complex 2 of the electron transport chain where $\text{FADH}_2$ enters, bypassing the first proton pump.

ATP Synthase

A membrane-spanning enzyme channel that acts like a turbine or water wheel, synthesizing ATP from ADP and inorganic phosphate as protons flow through it via facilitated diffusion.

Chemiosmosis

The production of ATP driven by the facilitated diffusion of hydrogen ions ($H^+$) down their concentration gradient through ATP synthase across the inner mitochondrial membrane.

Oxygen ($O_2$) in Aerobic Respiration

The terminal electron acceptor in the electron transport chain, which possesses high electron affinity and combines with electrons and hydrogen ions to produce water ($H_2O$).

Cyanide

A toxic compound that binds permanently to a protein complex within the electron transport chain, halting electron movement, shutting down ATP production, and leading to cell death.

Symporter Membrane Transport Cost

An active transport mechanism in certain cells that expends $1\,\text{ATP}$ per pyruvate ($2\,\text{ATP}$ per glucose) to pump pyruvate into the mitochondrial matrix, reducing net yield from $38\,\text{ATP}$ to $36\,\text{ATP}$.

Anaerobic Respiration

A cellular respiration pathway utilized in oxygen-depleted environments by organisms such as bacteria, utilizing alternative electron acceptors like nitrates, sulfates, iron, or manganese to produce roughly $20\,\text{ATP}$.

Lactic Acid Fermentation

An anaerobic metabolic process in muscle cells that converts $3\text{-carbon}$ pyruvate into $3\text{-carbon}$ lactic acid, regenerating $\text{NAD}^+$ to keep glycolysis running and yielding $2\,\text{ATP}$.

Alcoholic Fermentation

An anaerobic metabolic pathway in yeast that breaks down $3\text{-carbon}$ pyruvate into $2\text{-carbon}$ acetaldehyde and then into ethanol, releasing $CO_2$, regenerating $\text{NAD}^+$, and producing $2\,\text{ATP}$.

Fuel Switching

A metabolic transition induced by low-carbohydrate diets (e.g., Atkins or keto) that redirects cellular respiration to burn fats and proteins; amino acids enter at pyruvate, acetyl CoA, or the Krebs cycle, while glycerol and fatty acids enter around stage one.