Chapter 6: How Cells Harvest Chemical Energy - Vocabulary Flashcards

A set of vocabulary flashcards covering key terms, processes, and concepts from Chapter 6: How Cells Harvest Chemical Energy.

Photosynthesis

The cellular process occurring in chloroplasts that captures energy from sunlight to convert carbon dioxide and water into glucose and oxygen gas ($6\,\text{CO}_2 + 6\,\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2$).

Cellular Respiration

The aerobic process by which cells harvest chemical energy from food (glucose) to produce ATP, releasing carbon dioxide and water ($\text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2 \rightarrow 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + \text{ATP}$).

Kilocalorie (kcal)

The amount of heat required to raise the temperature of $1\,\text{kg}$ of water by $1\,^\circ\text{C}$.

Oxidation-Reduction Reaction

Also known as a redox reaction, a chemical reaction involving the movement of electrons from one molecule to another.

Oxidation

The loss of electrons from a molecule during an oxidation-reduction reaction.

Reduction

The gain of electrons by a molecule during an oxidation-reduction reaction.

Dehydrogenase

An enzyme that removes hydrogen atoms from organic molecules during cellular respiration.

NAD+

Nicotinamide adenine dinucleotide; an organic coenzyme that shuttles electrons, becoming reduced to NADH when accepting two electrons and oxidized when giving them up.

Coenzyme

A non-protein helper molecule, typically an organic molecule such as a vitamin, required for an enzyme to function properly.

Glycolysis

The initial stage of cellular respiration occurring in the cytoplasm that breaks down one 6-carbon glucose molecule into two 3-carbon pyruvate molecules, producing a net gain of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Energy Investment Phase

The first four reactions of glycolysis in which $2\,\text{ATP}$ molecules are consumed to add phosphate groups to glucose before it splits into two G3P molecules.

Energy Payoff Phase

The final five reactions of glycolysis that produce $4\,\text{ATP}$ molecules by substrate-level phosphorylation, $2\,\text{NADH}$, and $2$ pyruvate molecules.

Substrate-Level Phosphorylation

A metabolic mechanism of ATP formation in which an enzyme directly transfers a phosphate group from an organic molecule to ADP.

Pyruvate Oxidation

The mitochondrial process following glycolysis where a carbon atom is removed from pyruvate as $\text{CO}_2$, NAD+ is reduced to NADH, and Coenzyme A joins the remaining two-carbon group to form Acetyl CoA.

Acetyl CoA

A two-carbon compound bound to Coenzyme A, produced during pyruvate oxidation to enter the citric acid cycle.

Citric Acid Cycle

Also known as the Krebs cycle, a mitochondrial process that processes two acetyl CoA molecules per glucose, yielding $2\,\text{ATP}$, $4\,\text{CO}_2$, $6\,\text{NADH}$, and $2\,\text{FADH}_2$ after two turns.

Citrate

A six-carbon molecule formed in step 1 of the citric acid cycle when a two-carbon acetyl group enters the cycle.

Oxidative Phosphorylation

The third stage of cellular respiration in the mitochondria, comprising the electron transport chain and chemiosmosis, requiring oxygen and generating approximately $28\,\text{ATP}$ molecules (about $86\%$ of total ATP yield).

Electron Transport Chain

A collection of electron carrier molecules in the inner mitochondrial membrane that pass electrons sequentially like a staircase, pumping $\text{H}^+$ across the membrane to create a gradient.

Chemiosmosis

The process in which the flow of $\text{H}^+$ down its concentration gradient drives the phosphorylation of ADP to generate ATP.

Rotenone

A poison derived from the roots of tropical plants in South America and Southeast Asia that blocks the electron transport chain; used as a pesticide and in fish management to eradicate undesirable fish species.

Fermentation

An anaerobic pathway for harvesting chemical energy from glucose that utilizes glycolysis to generate $2\,\text{ATP}$ molecules per glucose while providing a mechanism to recycle NADH back to NAD+.

Lactic Acid Fermentation

An anaerobic process in which pyruvate is reduced to lactate while oxidizing NADH to NAD+; occurs in muscle cells during strenuous exercise and in certain bacteria.

Alcohol Fermentation

An anaerobic process carried out by yeast and bacteria where pyruvate is converted to $\text{CO}_2$ and ethanol while oxidizing NADH to NAD+.

Obligate Anaerobes

Organisms that require anaerobic conditions to generate ATP through fermentation and are poisoned by oxygen.

Facultative Anaerobes

Organisms, such as yeast and many bacteria, that can produce ATP using either fermentation or oxidative phosphorylation depending on oxygen availability.