Chapter 13: How Cells Obtain Energy from Food

Vocabulary flashcards covering the stages of cellular respiration, individual steps and enzymes of glycolysis, the citric acid cycle, metabolic regulation, gluconeogenesis, and energy storage polymers from Chapter 13.

Catabolism

A set of enzyme-catalyzed reactions by which complex molecules are degraded to simpler ones with the release of energy.

Stage 1 (Digestion)

The stage of catabolism where enzymes convert large molecules in food into simpler monomeric subunits; occurs outside cells or in lysosomes.

Stage 2 (Glycolysis)

The stage of catabolism that splits each molecule of glucose into pyruvate in the cytosol, generating ATP and NADH.

Kinase

An enzyme that catalyzes the addition of a phosphate group to molecules, transferring a phosphate group from ATP to substrate in steps 1 and 3 of glycolysis, or transferring a phosphate from ADP to ATP in steps 7 and 10.

Isomerase

An enzyme that catalyzes the rearrangement of bonds within a single molecule in steps 2 and 5 of glycolysis to prepare molecules for chemical alterations.

Dehydrogenase

An enzyme that catalyzes the oxidation of a molecule by removing a hydrogen atom and electron, such as glyceraldehyde 3-phosphate dehydrogenase in step 6.

Mutase

An enzyme that catalyzes the shifting of a chemical group from one position to another within a molecule.

Substrate-level phosphorylation

The process by which ATP is formed by the transfer of a phosphate group from a substrate molecule carrying a high-energy covalent bond to ADP.

Fermentation

The breakdown of organic molecules without the involvement of molecular oxygen, yielding less energy than aerobic cell respiration.

Hexokinase

The enzyme that transfers a phosphate group from ATP to glucose to make G6P, consuming 1 ATP and trapping glucose inside the cell.

Phosphoglucose isomerase

The enzyme that converts G6P into F6P during glycolysis.

PFK-1

The enzyme that transfers a phosphate group from ATP to F6P to make FBP; represents the rate-limiting step of glycolysis and uses 1 ATP.

Aldolase

The enzyme that splits FBP into DHAP and GAP during the cleavage step of glycolysis.

Triose phosphate isomerase

The enzyme that converts DHAP into GAP during glycolysis.

GAPDH

The enzyme that oxidizes GAP by transferring electrons to NAD- to make NADH and adds an inorganic phosphate to make BPG, producing 2 NADH.

Phosphoglycerate kinase

The enzyme that transfers a phosphate group from BPG to ADP, yielding ATP and 3PG, and producing 2 ATP in total.

Phosphoglycerate mutase

The enzyme that moves the phosphate group on 3PG to produce 2PG.

Enolase

The enzyme that removes $H_2O$ from 2PG to produce PEP during glycolysis.

Pyruvate kinase

The enzyme that transfers a phosphate group from PEP to ADP to form ATP and pyruvate, generating 2 ATP and 2 pyruvate.

Pyruvate dehydrogenase complex

An enzyme complex in the mitochondrial matrix that decarboxylates pyruvate to produce $CO_2$, NADH, and acetyl CoA.

Citrate synthase

The enzyme that catalyzes the reaction joining acetyl CoA to oxaloacetate to form citrate, releasing Coenzyme A.

Aconsitase

The enzyme that rearranges citrate into its isomer, isocitrate, through the removal and addition of $H_2O$.

Isocitrate dehydrogenase

The enzyme that oxidizes and decarboxylates isocitrate to a-ketoglutarate, releasing $CO_2$ and reducing NAD to NADH in the rate-limiting step of the citric acid cycle.

a-ketoglutarate dehydrogenase complex

An enzyme complex that oxidizes a-ketoglutarate, releasing a second $CO_2$ and NADH, and attaches Coenzyme A to form succinyl-CoA.

Succinyl-CoA synthetase

The enzyme that converts succinyl-CoA into succinate while producing GTP.

Succinate dehydrogenase

The enzyme that oxidizes succinate to fumarate while reducing FAD to FADH.

Fumarase

The enzyme that adds $H_2O$ to fumarate to convert it into malate.

Malate dehydrogenase

The enzyme that oxidizes malate to regenerate oxaloacetate while reducing NAD to NADH.

Gluconeogenesis

A set of enzyme-catalyzed reactions by which glucose is synthesized from small organic molecules such as pyruvate, lactate, or amino acids, bypassing irreversible steps 1, 3, and 10 of glycolysis.

Glycogen

A branched polymer composed exclusively of glucose units that is used to store energy in animal cells.

Glycogen phosphorylase

The enzyme that breaks down glycogen into G1P (which is converted to G6P for glycolysis); it is inhibited by G6P.

Glycogen synthase

The enzyme that synthesizes glycogen; it is activated by G6P.

Starch

A polysaccharide composed exclusively of glucose units used for energy storage in plant cells and stored in chloroplasts.