Glucose Oxidation

Glycolysis

Breakdown of glucose (6C) into 2 molecules of pyruvic acid (3C) in the presence of O2, or 2 molecules of lactic acid (3C) in the absence of O2.

Cytosol

The site where glycolysis takes place in all cells.

Net ATP and NADH production in glycolysis

2 ATP and 2 NADH are produced.

Phase 1 of Glycolysis

Energy Investment phase where glucose is converted into 2 molecules of Glyceraldehyde 3-P, consuming 2 ATPs.

Phase 2 of Glycolysis

Energy Payoff phase where Glyceraldehyde 3-P is converted to pyruvate, producing ATP and NADH.

Fate of pyruvate under anaerobic conditions

In anaerobic conditions, pyruvate is converted to lactic acid.

Fate of pyruvate under aerobic conditions

In aerobic conditions, pyruvate enters the mitochondria for oxidative decarboxylation.

ATP production in aerobic glycolysis

8 ATP (2 direct, 6 from NADH) is produced.

ATP production in anaerobic glycolysis

2 ATP is produced through substrate-level phosphorylation.

Regulation of glycolysis by ATP and NADH

High levels of ATP and NADH downregulate glycolytic enzymes.

Rate-limiting enzymes in glycolysis

Glucokinase/hexokinase, phosphofructokinase-1, and pyruvate kinase catalyze irreversible reactions.

Clinical relevance of inherited pyruvate kinase deficiency

It causes hemolytic anemia because RBCs rely on glycolysis for ATP production.

Insulin's effect on glycolytic enzymes

Insulin stimulates glycolytic enzymes.

Glucagon's effect on glycolytic enzymes

Glucagon represses glycolytic enzymes.

Oxidative decarboxylation of pyruvate

Pyruvate is converted to Acetyl CoA, CO2, and NADH+H in the mitochondria.

Enzymes required for oxidative decarboxylation

Pyruvate dehydrogenase complex with NAD, FAD, CoA-SH, TPP, and lipoic acid.

Products of oxidative decarboxylation of pyruvate

1 Acetyl CoA, 1 CO2, and 1 NADH+H are produced.

Fate of Acetyl CoA and NADH+H

Acetyl CoA enters the Krebs cycle, and NADH+H enters the electron transport chain (ETC).

Krebs cycle

Complete oxidation of acetyl CoA to 2 CO2, producing ATP, NADH, and FADH2 in the mitochondria.

Products of one turn of the Krebs cycle

2 CO2, 1 ATP, 3 NADH+H, and 1 FADH2 are produced from one acetyl CoA.

Two main phases of the Krebs cycle

Condensation of Acetyl CoA with oxaloacetate to form citrate, followed by oxidation reactions to regenerate oxaloacetate.

Regulation of the Krebs cycle

Allosterically regulated at citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.

Final common metabolic pathway significance of the Krebs cycle

It oxidizes carbohydrates, fats, and proteins.

ATP yield from one molecule of acetyl CoA

12 ATP produced (1 ATP from substrate-level phosphorylation, 2 ATP from FADH2, 9 ATP from 3 NADH).

End products of complete glucose oxidation

38 ATP and 6 CO2 are produced.

ATP production summary from glucose metabolism

Glycolysis: 2 ATP, Oxidative Decarboxylation: 6 ATP, Krebs Cycle: 24 ATP.

Comparison of anaerobic and aerobic glycolysis

Anaerobic glycolysis produces only 2 ATP, while aerobic glycolysis produces 38 ATP.