13. Metabolism 2; fate of pyruvate

Question 1

How is the REDOX balance maintained?

Answer 1

• only limited amounts of NAD+ are present in the cell
• NAD+ is derived from niacin (a vitamin)
• Glycolysis reduces NAD+ to NADH and H+
• NAD must be reoxidised to let glycolysis continue
• NAD+ is regenerated through the metabolism of pyruvate

Question 2

What conditions does glycolysis and cellular respiration occur?

Answer 2

Aerobic conditions with oxygen present

Question 3

What conditions does glycolysis and fermentation occur?

Answer 3

Anaerobic conditions with oxygen absent

Question 4

Describe the process of glycolysis and cellular respiration under aerobic conditions

Answer 4

• glycose to pyruvate (glycolysis)
• pyruvate undergoes pyruvate oxidation
• enters the citric acid cycle
• Electron transport chain/ ATP synthesis
• generates CO2 and H20
  and cn undergo further oxidation

Question 5

Describe the process of glycolysis and fermentation under anaerobic conditions

Answer 5

• Glucose to pyruvate (glycolysis)

- fermentation (cofactors are generated) where pyruvate is converted into lactate or alcohol

Question 6

What is the electron acceptor and enzyme involved in the generation of alcohol?

Answer 6

electron acceptor- acetaldehyde

enzyme- alcohol hydrogenase

Question 7

What is the enzyme involved in the generation of lactate?

Answer 7

lactate dehydrogenase

Question 8

What is the summary reaction of lactic acid fermentation?

Answer 8

Glucose + 2ADP + 2Pi to 2 lactate and 2ATP

Question 9

When does lactic acid fermentation occur?

Answer 9

during training and anaerobic exercise when there is less oxygen available

Question 10

Can lactate be converted into pyruvate?

Answer 10

yes

Question 11

What is the summary reaction of alcoholic fermentation?

Answer 11

Glucose + 2ADP +2Pi to 2 Ethanol + 2CO2 +2ATP

2 CO2 are generated from the 2 pyruvate

Question 12

List components of the mitochondria and what they contain

Answer 12

inner membrane; contain protein for electron transport chain, ATP synthase and transport proteins

matrix; contain enzymes for the TCA cycle

Question 13

Aerobic metabolism of pyruvate

Answer 13

• pyruvate enters the cell via a specific transporter

- there the pyruvate dehydrogenase complex catalyses the oxidative decarboxylation of pyruvate to acetyl-coA

Question 14

Pyruvate dehydrogenase complex

Answer 14

• contains 3 enzymes (E1, E2, E3) and 2 enzymes involved in the control of the PDC
• a kinase and phosphatase in a single peptide
• plus co-enzymes (thiamine, lipoid acid, coenzyme A, FAD, NAD+
• the reaction is irreversible
• Acetyl-coA cannot be converted into pyruvate