Glycolysis & Pentose Phosphate Pathway

Molecular formula of glucose

C6H12O6.

Universal fuel used by all cells

Glucose.

Cells relying solely on glycolysis for ATP

Erythrocytes (RBCs).

ATP

Adenosine triphosphate—the cell's energy currency.

Dephosphorylation of ATP

ATP → ADP + Pi with release of energy.

End product of glycolysis per glucose

2 pyruvate.

Net ATP generated by glycolysis per glucose

2 ATP (net).

Pyruvate in anaerobic conditions

Reduced to lactate by lactate dehydrogenase (LDH).

Pyruvate in aerobic metabolism

Converted to acetyl-CoA → TCA cycle → large ATP yield.

Investment phase of glycolysis

Uses 2 ATP to phosphorylate glucose to fructose-1,6-bisphosphate.

Payoff phase of glycolysis

Generates 4 ATP and 2 NADH (net +2 ATP overall).

Committed, rate-limiting step of glycolysis

PFK-1: fructose-6-phosphate → fructose-1,6-bisphosphate (irreversible).

Step that splits the 6-carbon sugar

Aldolase cleavage of fructose-1,6-bisphosphate.

3-carbon intermediate entering payoff reactions

Glyceraldehyde-3-phosphate (G3P).

Enzyme converting PEP to pyruvate

Pyruvate kinase (irreversible).

Three irreversible glycolytic steps

Hexokinase/Glucokinase, PFK-1, Pyruvate kinase.

Glycolytic intermediates feeding into

Fat, protein, nucleic acid metabolism, and the pentose phosphate pathway.

Metabolite where PPP branches from glycolysis

Glucose-6-phosphate.

Why is the PPP called a shunt?

Excess pentose phosphates can be recycled back into glycolysis.

Primary product of PPP for nucleotide synthesis

Ribose-5-phosphate.

Major reducing equivalent produced by PPP

NADPH.

Key biosynthetic uses of NADPH

Synthesis of fatty acids, cholesterol, steroid hormones, and bile salts.

Antioxidant role of NADPH in RBCs

Maintains reduced glutathione to protect against oxidative damage.

Clinical consequence of G6PD deficiency

Hemolytic anemia due to impaired glutathione regeneration.

Enzyme regenerating NAD+ for glycolysis under anaerobic conditions

Lactate dehydrogenase (LDH).

What regenerates NAD+ in aerobic cells?

Mitochondrial electron transport chain (oxidative phosphorylation).

Fate of lactate produced in muscle

Cori cycle: transported to liver → converted back to glucose.

Hexokinase vs glucokinase—primary tissue distribution

Hexokinase: most tissues; Glucokinase: liver/pancreas.

Glycolysis overall purpose in fasted vs fed state

Fed: ATP + precursors; Fasted/hypoxia: ATP rapidly via anaerobic glycolysis.

Rate-limiting enzyme of PPP oxidative phase

Glucose-6-phosphate dehydrogenase (G6PD).

Step of glycolysis producing NADH

Glyceraldehyde-3-phosphate dehydrogenase: G3P → 1,3-BPG.

Substrate-level phosphorylations in glycolysis

1,3-BPG → 3-PG (phosphoglycerate kinase) and PEP → pyruvate (pyruvate kinase).

Net NADH produced by glycolysis per glucose

2 NADH (cytosolic).

Clinical marker for tissue hypoxia related to glycolysis

Elevated serum lactate (lactic acidosis).

Location of glycolysis within the cell

Cytosol.

Location of PPP within the cell

Cytosol.