Energy Production - Stages 1 & 2

Question 1

What is the net synthesis of ATP per mole of glucose in glycolysis?

Answer 1

• 2 net ATP synthesised

- 2 ATP used, 4 generated

Question 2

Name the key regulatory enzyme(s) involved during the conversion of Glucose —> Glucose-6-P during stage 1 of glycolysis

Answer 2

• Hexokinase (low Km for glucose)

- Glucokinase (only in liver, high Km for glucose)

Question 3

What are the advantages of PHOSPHORYLATION?

Answer 3

• Makes sugar anionic (-ve) so cannot cross plasma membrane
• Increases reactivity of sugar
• Allows formation of compounds with high-energy phosphoryl transfer potential (so can convert ADP–>ATP via substrate level phosphorylation)

Question 4

Explain how ATP is produced in glycolysis

Answer 4

Substrate level phosphorylation during stages 7 and 10 each produce 2 ATP per molecule of glucose

Question 5

Why is stage 10 of glycolysis irreversible?

Answer 5

Large -ve ΔG

Question 6

State 2 intermediates of glycolysis which are used elsewhere in other metabolic pathways

Answer 6

• Dihydroxyacetate phosphate (DHAP) is converted to GLYCEROL PHOSPHATE which is required for the synthesis of TAGs in liver and adipose tissue
• 2,3-Bisphosphoglycerate (2,3-BPG) is an important regulator for the affinity of Haemoglobin for oxygen (decreases affinity so O2 is released as tissues)

Question 7

What are the 3 key regulatory enzymes in glycolysis?

Answer 7

• Hexokinase
• Phosphofructokinase (PFK)
• Pyruvate kinase

Question 8

Explain how Hexokinase activity is regulated

Answer 8

ALLOSTERICALLY INHIBITED by Glucose-6-phosphate (product)

Question 9

Describe 2 ways in which PFK can be regulated

Answer 9

• ALLOSTERICALLY in muscle (inhibited by high ATP:ADP ratio)

- HORMONAL in liver (inhibited by high insulin:glucagon ratio)

Question 10

What are the main products of glycolysis?

Answer 10

• ATP
• NADH
• Pyruvate (3C)

Question 11

Why is PFK considered the key regulatory enzyme in controlling the rate of glycolysis?

Answer 11

• ALLOSTERICALLY REGULATED
• Activated by low energy signals such as ADP, NAD+ and glucagon
• Inhibited by high energy signals such as ATP, NADH and insulin
• DEPHOSPHORYLATION of PFK depends on ATP:ADP ratio
• Low level of enzyme will slow rate of glycolysis

Question 12

Explain how glycolysis can occur anaerobically

Answer 12

• Pyruvate —> Lactate using LACTATE DEHYDROGENASE and NADH
• NADH —> NAD+ which can then re-enter glycolysis and small amounts of ATP can be produced
• Lactate can be converted back into Pyruvate at the liver

Question 13

Describe the cause(s) of lactic acidosis

Answer 13

• Elevations of lactate (>5mmol/L) in blood can affect the buffering capacity of plasma, causing lactic acidosis
• Increased levels of lactate may be due to strenuous exercise or decreased utilisation of lactate in liver (due accumulation of acetaldehyde during alcohol metabolism)

Question 14

Why are some stages in glycolysis irreversible?

Answer 14

• Some of the reactions in glycolysis are RATE DETERMINING STEPS
• Cannot simply be reversed as other enzymes (phosphatases) are needed for the dephosphorylation of certain substances