LECTURE 21 - GLUCONEOGENESIS & KETOGENESIS

Question 1

Identify the regulation mechanism to suppress glycolysis and to promote gluconeogenesis

Answer 1

ATP inhibits 6-phosphofructo-1-kinase and pyruvate kinase

(ATP = high energy = don’t need to generate more ATP)

Question 1

Identify the carbon source(s) of gluconeogenesis

Answer 1

Lactate
Amino acids
Glycerol
Fructose

Question 2

Identify the rate-limiting step of gluconeogenesis

Answer 2

The step catalyzed by phosphoenolpyruvate (PEP) carboxykinase

Question 3

Explain the roles of glucokinase and glucose 6-phosphatase in the regulation of blood glucose levels by the liver

Answer 3

The futile cycle formed by glucokinase and glucose 6-phosphatase keeps the cellular glucose concentration high

Question 4

Explain how alcohol interferes with gluconeogenesis

Answer 4

1) Oxidation of ethanol by the liver depletes NAD+ in the cytosol
2) Excess NADH converts pyruvate to lactate
3) Gluconeogenesis by the liver is suppressed
4) This may cause hypoglycemia and alcohol-included lactic acidosis

– The problem is more severe when the glycogen storage in the liver is depleted under malnutrition or after a strenuous exercise.

Question 5

Explain the role(s) of pentose phosphate pathway in metabolism

Answer 5

Produces NADPH, the major reducing equivalent for biosynthesis

Produces ribose-5-phosphate, which is used for DNA & RNA synthesis

Question 6

List the fates of glucose 6-phosphate in cells

Answer 6

• Glycolysis
• Glycogen synthesis
• Pentose Phosphate Pathway
• Glucose production (only in the liver)

Question 7

What is the biochemical role of NADH?

Answer 7

generation of ATP by oxidative phosphorylation

Question 8

What is the biochemical role of NADPH?

Answer 8

reducing cofactor in anabolic reactions

Question 9

Identify the conditions under which ketone bodies are produced

Answer 9

Produced mostly by the liver during prolonged fasting or on a ketogenic diet (low carbohydrate & high fat)

Question 10

Explain how ketone bodies are utilized to produce energy

Answer 10

• They are converted to acetyl-CoA in the mitochondria of non-hepatic (non-liver) tissues
• Acetyl-CoA is used as fuel in the TCA cycle
  (In the presence of oxygen ONLY)
• The reducing equivalent of β-hydroxybutyric acid is harvested as NADH

Question 11

Explain how glucose is reserved when O2 is sufficient

Answer 11

The body uses fatty acids & ketone bodies in the presence of oxygen to save glucose for anaerobic fermentation