Chapter 6: How Cells Obtain Energy - Cellular Respiration and Fermentation

Comprehensive vocabulary flashcards covering the stages of cellular respiration, redox chemistry, ATP synthesis mechanisms, and fermentation pathways from Chapter 6.

Metabolism

The complete set of all chemical reactions that take place within an organism.

Anabolic Reactions

Metabolic pathways in which small molecules are built into larger ones; these reactions require energy and are typically endergonic.

Catabolic Reactions

Metabolic pathways in which large molecules are broken down into smaller ones; these reactions release energy and are typically exergonic.

Cellular Respiration

The controlled aerobic breakdown of organic fuel molecules (such as carbohydrates, lipids, and proteins) to harvest chemical energy stored in covalent bonds and produce ATP, $CO_2$, and $H_2O$.

Redox Reaction

An oxidation-reduction reaction characterized by the movement or transfer of electrons (or hydrogen atoms, $H:^-$) from one molecule to another.

Oxidation

The loss of one or more electrons (or $H:^-$) from a substance during a chemical reaction.

Reduction

The addition or gain of one or more electrons (or $H:^-$) by a substance during a chemical reaction.

$$NAD^+$$

A coenzyme derived from niacin that serves as an electron carrier in cellular respiration, accepting $2\text{ electrons}$ and a proton to become reduced to NADH.

Riboflavin

Vitamin $B_2$, an essential nutrient that forms the structural basis of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).

Substrate-Level Phosphorylation

A mode of ATP synthesis occurring in glycolysis and the citric acid cycle where an enzyme directly transfers an inorganic phosphate group ($P_i$) from an organic substrate molecule to ADP.

Glycolysis

The initial stage of cellular respiration in the cytoplasm where a single molecule of glucose ($C_6H_{12}O_6$) is broken down into two molecules of pyruvate ($2 \times C_3$), generating a net yield of $2\text{ ATP}$ ($4\text{ ATP}$ generated $- 2\text{ ATP}$ consumed) and $2\text{ NADH}$.

Pyruvate Oxidation

The intermediate stage occurring in the mitochondria where pyruvate has a carboxyl group removed as $CO_2$, is oxidized to reduce $NAD^+$ to NADH, and joins coenzyme A to form acetyl CoA.

Citric Acid Cycle

Also called the Krebs cycle or TCA cycle; a metabolic pathway in the mitochondria that oxidizes acetyl CoA into $CO_2$, producing $2\text{ }CO_2$, $3\text{ NADH}$, $1\text{ ATP}$, and $1\text{ }FADH_2$ per acetyl CoA ($4\text{ }CO_2$, $6\text{ NADH}$, $2\text{ ATP}$, and $2\text{ }FADH_2$ per glucose).

Electron Transport Chain

A series of protein complexes and mobile carriers embedded in the inner mitochondrial membrane that transfer electrons from NADH and $FADH_2$ to $O_2$, utilizing the released energy to pump protons ($H^+$) into the intermembrane space.

Chemiosmosis

An energy-coupling mechanism in which a proton concentration gradient across the inner mitochondrial membrane drives the synthesis of ATP as $H^+$ diffuses back into the matrix.

$$F_1F_o\text{ ATP Synthase}$$

A membrane enzyme complex composed of an $F_o$ rotor embedded in the membrane and an $F_1$ catalytic headpiece that synthesizes ATP from ADP and $P_i$ using the energy of a proton gradient.

Oxidative Phosphorylation

The final stage of cellular respiration comprising the electron transport chain and chemiosmosis, generating approximately $28\text{ ATP}$ per glucose molecule across the inner mitochondrial membrane.

Fermentation

An anaerobic pathway for harvesting chemical energy that relies on glycolysis to produce a net of $2\text{ ATP}$ per glucose while providing an alternative mechanism to recycle NADH back to $NAD^+$ in the absence of oxygen.

Lactic Acid Fermentation

An anaerobic process occurring in muscle cells and some bacteria where NADH transfers electrons directly to pyruvate, reducing pyruvate to lactate and regenerating $NAD^+$ to keep glycolysis functioning.

Alcohol Fermentation

An anaerobic process utilized by yeasts where pyruvate is converted to $CO_2$ and reduced by NADH to ethanol ($C_2H_5OH$), regenerating $NAD^+$ for glycolysis.