3 - Glycolysis

Question 1

What is this process:

One mole of a 6 carbon sugar is broken down in ten steps into two moles of a 3 carbon sugar

Answer 1

Glycolysis

GLucose to pyruvate

Two phases:

• Energy investment phase
• Energy generation phase

Question 2

What is the equation for the aerobic glycolysis reaction?

Answer 2

Glucose + 2ADP + 2Pi + 2NAD+ -> 2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O

Question 3

What is the goal of fermentation?

Answer 3

To re-oxidize NADH to NAD+ so glycolysis can continue without changing the oxidation state

Homolactic fermentation also occurs in muscle tissue when pyruvate is produced faster than it can be oxidized

Question 4

Give the five reactions involved in the investment phase of glycolysis

Answer 4

1. Glucose to glucose-6-phosphate (hexokinase), ATP/Mg dependent and irreversible
2. Isomerization of G-6-P to F-6-P (phosphoglucoisomerase), facilitates phosphorylation at C1 in reaction 3, reversible
3. F-6-P to F-1,6-bisP (PFK-1), ATP/Mg dependent, irreversible, RLS
4. Cleavage to triose phosphate (F-1,6-bisP aldolase), reversible
5. Isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate (triose phosphate isomerase), reversible

Question 5

Give the five reactions of the energy generation phase of glycolysis

Answer 5

6. glyceraldehyde-3-phosphate to high energy acylphosphate (glyceraldehyde-3-phosphate dehydrogenase), NAD+ to NADH, reversible
7. Substrate level phosphorylation (phosphoglycerate kinase). Phosphate transferred to ADP to form ATP, highly exergonic/favoured/irreversible
8. 3-Phosphoglycerate activated (phosphoglycerate mutase), dependent on Mg and high conc of substrate, reversible
9. Synthesis of phosphoenolpyruvate (PEP) by enolase, dehydration reaction, reversible
10. Second substrate level phosphorylation to pyruvate (pyruvate kinase) produces ATP, highly regulated, activated by F-1,6-bisP and induced by carbo loading, exergonic even with the ADP to ATP coupling

Question 6

How many moles of ATP does glycolysis release per mole of glucose

Answer 6

Aerobic: 8
Anaerobic: 2

Question 7

How is glycolysis regulated?

Answer 7

PFK

• Oxygen inhibits
• AMD, ADP promote tetramerization (activate)
• F-2,6-bisP also activates
• ATP and citric acid (citrate) inhibit by reducing affinity for substrate

Pyruvate Kinase

• ATP inhibits
• F-1,6-bisP activates
• Acetyl-CoA inhibits to reduce glycolysis when fat oxidation is energy source

Hexokinase
- G-6-P inhibits

Glycogen phosphorylase
- ?

Glycolysis intermediates are also used for synthesis of amino acids and lipids. Therefore multiple regulatory sites are important to satisfy the substrate requirements for these reactions

Question 8

List six sugars that can feed into glycolysis somehow

Answer 8

Galactose: Epimerization produces G-6-P

Fructose (phosphorylation to F-1-P will bypass PFK and cause buildup and enhanced triglyceride synthesis)

Mannose: Phosphorylated to mannose-6-P by hexokinase, isomerization produces F-6-P

Maltose: 2 glucose by maltase

Lactose: galactose + glucose by lactase in gut

Sucrose: fructose + glucose (sucrase)

Glycerol: liberated by digestion of phospholipids and triacylglycerols, phosphorylated to glycerol-3-P by glycerokinase