Glycolysis

What is glycolysis?

A 10-step metabolic pathway that converts 1 glucose → 2 pyruvate + 2 ATP (net) + 2 NADH.

What are the two phases of glycolysis?

• Phase 1: Energy investment (uses 2 ATP)

• Phase 2: Energy payoff (produces 4 ATP + 2 NADH)

What are the products of glycolysis?

2 Pyruvate, 2 ATP (net), 2 NADH.

What enzyme phosphorylates glucose in step 1?

Hexokinase (or Glucokinase in liver)

Why is glucose phosphorylation important in step 1?

It traps glucose in the cell and destabilizes it for further breakdown.

Which enzyme converts glucose-6-phosphate to fructose-6-phosphate?

Phosphoglucose isomerase

What is the committed step of glycolysis?

Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase-1 (PFK-1)

Which enzyme splits fructose-1,6-bisphosphate?

Aldolase

Which enzyme interconverts DHAP and GAP?

Triose phosphate isomerase

Which enzyme oxidizes GAP to 1,3-bisphosphoglycerate?

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)

Which enzyme produces ATP from 1,3-BPG?

Phosphoglycerate kinase (substrate-level phosphorylation)

What does enolase do?

Removes water from 2-phosphoglycerate to form phosphoenolpyruvate (PEP)

What enzyme converts PEP to pyruvate and generates ATP?

Pyruvate kinase

Which 3 enzymes are major regulatory points in glycolysis?

Hexokinase, phosphofructokinase (PFK-1), pyruvate kinase.

What inhibits hexokinase?

Glucose-6-phosphate (product inhibition).

How is PFK-1 regulated?

• Inhibited by ATP, citrate, and H⁺

• Activated by AMP and fructose 2,6-bisphosphate.

What regulates pyruvate kinase?

• Allosterically activated by fructose-1,6-bisphosphate

• Inhibited by ATP and alanine.

What happens to pyruvate under aerobic conditions?

Converted to acetyl-CoA and enters the TCA cycle

What happens to pyruvate under anaerobic conditions in muscles?

Reduced to lactate via lactate dehydrogenase

What is alcoholic fermentation?

Pyruvate → Acetaldehyde → Ethanol; regenerates NAD⁺ (in yeast)

Why is regenerating NAD⁺ important?

It allows glycolysis to continue in anaerobic conditions

What is the Warburg effect?

Cancer cells prefer glycolysis (producing lactate) even in oxygen-rich conditions.

What is the role of HIF-1 in cancer?

Promotes glycolysis under low oxygen (hypoxia).

What is lactose intolerance?

Inability to break down lactose due to lack of lactase enzyme.

How does fructose enter glycolysis (liver)?

Converted to DHAP and GAP via fructokinase pathway.

How does galactose enter glycolysis?

Converted to glucose-1-phosphate then to glucose-6-phosphate

What enzyme is deficient in galactosemia?

Galactose-1-phosphate uridylyltransferase