Metabolism 1

Question 1

What is the process which makes ATP?

Answer 1

Oxidative phosphorylation.

ATP is made my ATP synthase, which requires a flow of H+ ions through it to work.

Question 2

Where do the hydrogen ions for ATP synthesis come from?

Answer 2

NADH and FADH₂.

These are oxidised within the mitochondrion releasing H+ ions and free electrons.

Question 3

What is the electron transport chain?

Answer 3

The flow of electrons across proton (H+) pumps in the inner mitochondrial membrane. This chain causes H+ ions to be pumped out of the mitochondrial matrix creating a gradient.

ATP is then produced when H+ ions flow back to the matrix through ATP synthetase channels.

Question 4

What is the Krebs cycle?

Answer 4

NADH and FADH2 come from the Kreb’s cycle.

• occurs in the mitochondrial matrix
• driven by acetyl CoA
• this combines with oxaloacetate to create citrate
• eight further steps producing:
  
  • 2 CO2
  • 1 ATP
  • 3 NADH and 1 FADH2
  • (uses O2, hence aerobic)

Question 5

What are carbohydrates broken down to?

Answer 5

Monosaccharides (eg glucose/fructose)

Question 6

What are proteins broken down to?

Answer 6

Amino acids

Question 7

What are fats broken down into?

Answer 7

Glycerol and FFAs.

(all except FFA can be converted into pyruvate, which is then converted into acetyl CoA)

Question 8

What is glycolysis?

Answer 8

• takes place in the cytoplasm
• glucose activated by phosphorylation to glucose-6-phosphate (requires ATP)
• 10 enzymatic reactions, 1 glucose = 2 molecules pyruvate
• pyruvate then converted to Acetyl CoA and enters Krebs cycle
• glycolysis produces 2 ATPs and 2 molecules NADH
• glycerol from fat also enters this pathway to become pyruvate

Question 9

How can amino acids enter the Kreb’s cycle?

Answer 9

Either by being converted pyruvate or directly via the Kreb’s cycle’s intermediate molecules.

Question 10

How do FFAs become acetyl CoA?

Answer 10

Directly through Beta-oxidation.

This occurs within the mitochondrion.

Byproduct is a ketoacid - which can access the Kreb’s cycle directly.

Question 11

How many ATPs does aerobic metabolism yield per glucose?

Answer 11

38 ATPs for one molecule of glucose if fully metabolized

Breakdown:
Glycolysis = 2

Kreb’s Cycle = 2

Oxidative Phosphorylation

• 2 NADH (from glycolysis) = 6
• 2 NADH (from pyruvate oxidation) = 6
• 6 NADH (from Kreb’s) = 18
• 2 FADH2 (from Kreb’s) = 4

Question 12

What are the steps in anaerobic metabolism?

Answer 12

1. Glucose converted to pyruvate requiring 2 ATPs
2. Glucose cannot be converted to acetyl CoA, so doesn’t enter Krebs
3. Pyruvate is converted to lactate (creating net 2 ATPs)
4. Once aerobic conditions restored lactate is transported back to the liver where it’s converted to glucose (Cori cycle)

Question 13

How can lactic acid enter the Kreb’s cycle?

Answer 13

• cannot enter Kreb’s cycle directly
• has to be converted back to glucose first via the Cori cycle
• or through conversion back to pyruvate

Question 14

Can anaerobic metabolism occur in RBCs?

Answer 14

Yes, therefore lactic acid can be formed in RBCs

Question 15

What is pyruvate converted into in anaerobic metabolism?

Answer 15

Lactic acid

Question 16

What are the end products of aerobic metabolism of glucose?

Answer 16

C6H12O6 + 6O2 → 6H2O + 6CO2 + 38ATP

• ATP
• H2O
• CO2

Question 17

Does glycolysis require O2?

Answer 17

No, it occurs in the cytoplasm and is anaerobic.

Question 18

What does acetyl CoA combine with in the 1st step of krebs cycle?

Answer 18

Acetyl CoA combines with oxaloacetate to produce citric acid

Question 19

How can amino acids enter the Kreb’s cycle?

Answer 19

Pyruvate but also via intermediate molecules (oxaloacetate, fumarate, succinate, alpha-ketoglutarate)

Question 20

What happens in the 1st 24hrs of starvation?

Answer 20

• glucose levels fall
• glycogen stores mobilise (glycogenolysis) to maintain basal plasma glucose concentration
• glycogen stores exhaust within 24hrs

Question 21

What happens in 24hrs - 4 days of starvation?

Answer 21

• pyruvate can be converted back to flucose
• pyruvate is generated from amino acids (protein breakdown) and glycerol (fat metabolism)
• these maintain plasma glucose concentration

Question 22

What happens in starvation >4days?

Answer 22

The body switches to predominantly fat metabolism to preserve protein (essential for body maintenance).

It uses ketoacids (by product of FFA metabolism) to drive the Kreb’s cycle instead of glucose. This is slow as hormone dependent (cortisol and GH).

Ultimately fat stores deplete, protein breakdown increases and death follows.

Question 23

Where in the body still require glucose as their primary energy substrate in starvation?

Answer 23

• erythrocytes
• renal medulla
• 50% of the CNS

It’s provided by amino acids and glycerol.

Question 24

What does starvation do to protein breakdown, glycogen synthesis, lipid metabolism, plasma glucose levels and cellular glucose uptake?

Answer 24

• increases protein breakdown (gluconeogenesis)
• decreases glycogen synthesis
• increased lipid metabolism
• decreased plasma glucose levels
• decreased cellular glucose uptake (cells begin using ketoacids instead)

Question 25

What do the renal cortex and medulla use for energy in starvation?

Answer 25

The renal cortex converts to using ketoacids

The renal medulla still uses glucose as it’s primary substrate

Question 26

What is glycogen broken down to in starvation?

Answer 26

Glucose

Question 27

Do enterocytes convert to ketoacid metabolism?

Answer 27

Yes

Question 28

How long does ketoadaptation take?

Answer 28

2 weeks