Campbell Biology: Chapter 7 - Cellular Respiration

Vocabulary review covering key concepts, chemical reactions, enzymes, and metabolic stages of cellular respiration from Chapter 7 of Campbell Biology in Focus.

Catabolic Pathway

A metabolic pathway that releases energy by breaking down complex organic molecules, such as glucose, into simpler compounds.

Redox Reactions

Coupled chemical reactions involving the transfer of one or more electrons from one reactant to another; short for oxidation-reduction reactions.

Oxidation

The complete or partial loss of electrons from a substance involved in a redox reaction, which decreases its negative charge and makes it more positive.

Reduction

The complete or partial addition of electrons to a substance involved in a redox reaction, which reduces the amount of positive charge.

Reducing Agent

The electron donor in a redox reaction that reduces another substance and becomes oxidized in the process.

Oxidizing Agent

The electron acceptor in a redox reaction that oxidizes another substance and becomes reduced in the process.

$$NAD^+$$

A coenzyme electron carrier that functions as an oxidizing agent during cellular respiration by accepting electrons and hydrogen to form $NADH$.

$$NADH$$

The reduced form of $NAD^+$ that represents stored energy tapped into to synthesize $\text{ATP}$ inside the mitochondria.

Glycolysis

A ten-step metabolic pathway located in the cytoplasm that breaks down one six-carbon glucose into two three-carbon pyruvate molecules without requiring oxygen.

Hexokinase

An enzyme in the first step of glycolysis that transfers a phosphate group from $\text{ATP}$ to glucose, producing glucose-6-phosphate.

Substrate-Level Phosphorylation

The enzyme-catalyzed formation of $\text{ATP}$ by direct transfer of a phosphate group from an organic substrate to $\text{ADP}$, occurring in glycolysis and the citric acid cycle.

Acetyl CoA

A two-carbon acetyl unit attached to coenzyme A produced by pyruvate oxidation in the mitochondrion that feeds into the citric acid cycle.

Citric Acid Cycle (Krebs Cycle)

An eight-step metabolic cycle in the mitochondrial matrix that decomposes citrate back to oxaloacetate, yielding $1\,\text{ATP}$, $3\,\text{NADH}$, and $1\,\text{FADH}_2$ per turn.

Oxaloacetate

The four-carbon molecule in the citric acid cycle that combines with the acetyl group of acetyl CoA to form citrate and is regenerated by step eight.

Oxidative Phosphorylation

The production of $\text{ATP}$ powered by the redox reactions of the electron transport chain and chemiosmosis, accounting for nearly $90\%$ of cellular respiration's $\text{ATP}$.

Cytochromes

Iron-containing proteins that function as electron carriers in the electron transport chain before passing electrons to oxygen.

Chemiosmosis

An energy-coupling mechanism that uses the energy stored in a hydrogen ion ($H^+$) gradient across a membrane to drive cellular work, such as $\text{ATP}$ synthesis.

Proton-Motive Force

The potential energy stored in an electrochemical hydrogen ion ($H^+$) gradient across the inner mitochondrial membrane.

ATP Synthase

A rotary molecular machine in the inner mitochondrial membrane that uses the exergonic flow of $H^+$ to phosphorylate $\text{ADP}$ into $\text{ATP}$.

Alcoholic Fermentation

An anaerobic catabolic pathway where pyruvate is converted to ethanol in two steps, releasing carbon dioxide and regenerating $NAD^+$ for glycolysis.

Lactic Acid Fermentation

An anaerobic pathway where pyruvate is directly reduced by $NADH$ to form lactate as an end product with no release of carbon dioxide.

Obligate Anaerobes

Organisms that carry out only fermentation or anaerobic respiration and cannot survive in the presence of oxygen.

Facultative Anaerobes

Organisms, such as yeasts and many bacteria, that can survive using either cellular respiration or fermentation depending on oxygen availability.

Beta Oxidation

A metabolic sequence that breaks fatty acids down into two-carbon fragments that enter the citric acid cycle as acetyl CoA.