Week 3 - Carbohydrate metabolism

Question 1

What are the functions of glycolysis?

Answer 1

• To oxidise glucose: synthesis of 2 NADH
• Synthesis of 2 net ATP
• Produces C6 and C3 intermediates: glycerol phosphate, 2,3-BPG

Question 2

What are the features of glycolysis?

Answer 2

• It is exergonic and oxidative.
• C6 is converted to 2 C3 with no loss of carbon dioxide.
• Can operate anaerobically
• Irreversible pathway

Question 3

Net equation for lactate dehydrogenase reaction?

Answer 3

NADH + Pyruvate + H+ —> Lactate + NAD+

Question 4

What is lactate produced by?

Answer 4

• Skeletal muscle (skin, brain, GI)

- RBC

Question 5

What is lactate metabolised by?

Answer 5

• Liver

- Heart

Question 6

Write the equation for the pentose phosphate pathway.

Answer 6

Glucose-6-phosphate –> C5 sugar + CO2
NADP+ —-> NADPH
-Release of carbon dioxide
-catalysed by glucose-6-phosphate dehydrogenase
C5 sugars are rearranged to glycolytic intermediates:
3C5 —> 2 Fructose -6- P + 1 glyceraldehyde-3-phosphate

Question 7

Write down the functions of the pentose phosphate pathway.

Answer 7

1. Produce NADPH in cytoplasm: biosynthetic reducing power (for example, for lipid synthesis - therefore, occurs more in liver and adipose tissue)
2. Maintain free -SH cysteine groups on certain proteins: prevent oxidation to S-S: this is important for the structural integrity and functional activity of some proteins (e.g. lens of the eye)
3. Produce C5 sugars for nucleotides for nucleic acid synthesis (occurs in rapidly dividing tissue - bone marrow)

Question 8

Glycolysis - Key points

Answer 8

• central pathway of CHO metabolism

- occurs in all tissues (cytosolic)

Question 9

What occurs in glucose-6-phosphate deficiency?

Answer 9

1. Functional activity of some proteins depends on free -SH groups.
2. Common inherited defect
3. For example, in red blood cells: reduced NADPH –> disulfide bonds form –> aggregated proteins –> Heinz bodies –> haemolysis