Topic 19 - Metabolic Pathways

Question 1

Learning Objectives

Answer 1

1. Distinguish between aerobic and anaerobic pathways
2. Describe the catabolism of fatty acids and amino acids for ATP production
3. Describe the processes involved in ATP production under anaerobic conditions
4. Explain the importance of lactic acid fermentation in regenerating NAD+ for glycolysis
5. Compare preferences for metabolic substrates between skeletal muscle, heart muscle and brain
6. Compare differences in metabolic substrates utilised by tissues under fed, fasting and starvation conditions

Question 2

Catabolism of Fatty Acids

Answer 2

• Fatty acid chain is broken into 2 carbon acetic acid molecules
  [heft]
• Often converted into Ketone bodies as Kreb Cycle cannot take in all Acetyl CoA

Question 3

Catabolism of Amino Acids

Answer 3

• Excess amino acids produced from digesting proteins are transporrted to the liver
• Amino acid degradation produces sugars (Pyruvate, Acetyl CoA)
• The Amino acid group (NH2) and (H) are removed to form NH3 (removed in urine)
• Non-Nitrogenous portion becomes a Ketone body
  *

Question 4

When O2 is limited

Answer 4

• Glycolysis still occurs and amino acids can be converted into pyruvate
• The lactic acid fermentation increases and is converted into lactate

Question 5

lactic acid fermentation

Answer 5

• Lactate production increases when the demand for ATp exeeds supply and O2 is limiting
• Pyruvate is reduced to form lactate
• NADH is oxidised to form NAD+

Question 6

ATP used for

Answer 6

95% of celllular energy source
- Contractility, motility
- Ion pumping
- Signalling
- Biosynthesis

Question 7

Fed Vs Fasting Vs Starving states

Answer 7

Fed:
- 4hr after meal
- tissue uses glucose from meal
- excess glucose stored as glycogen

Fasting:
- 4-30hr after meal
- Tissues other than brain reduce glucose usage
- Brain uses glucose from glycogen stores & amino acids in liver

Starving:
- after 30hr
- Brain starts using ketone bodies
- other tissues stop using glucose
- Liver makes ketones from fatty acids
- Liver and kidneys make glucose from amino acids

Question 8

Ketone Bodies

Answer 8

• Used as a fuel mainly in the brain, heart and skeletal muscle
• Abundant during periods of stress (post exercise, starvation, high fat diets)
• Almost entirely from fatty acids in liver

Question 9

Ketoacidosis

Answer 9

• High serum and urine concentrations of ketone bodies

Diabetic Ketoacidosis:
- Life threatening complication of uncontrolled diabetes

Starvation of Ketoacidosis:
- When body deprived of glucose and relies on fatty acids