eLFH - Metabolism Physiology Part 1

Question 1

Oxidative phosphorylation definition

Answer 1

Process by which Adenosine Triphosphate (ATP) is produced by ATP synthetase

Question 2

Requirement for oxidative phosphorylation to occur

Answer 2

Flow of H+ ions through ATP synthetase

Question 3

Location of ATP synthetase

Answer 3

Mitochondrial membrane

Question 4

How does mitochondrion source H+ ions

Answer 4

NADH and FADH2 are oxidised within mitochondrion

Results in release of H+ ions and free electrons (and NAD+ or FAD+)

Flow of free electrons across H+ ion pumps in the inner mitochondrial membrane (Electron transport chain) cause H+ ions to be pumped out of mitochondrial matrix to generate a gradient

ATP produced when H+ flow back into matrix through ATP synthetase

Question 5

Source of NADH and FADH2

Answer 5

Krebs cycle

aka Tricarboxylic acid cycle

aka Citric acid cycle

Question 6

Where does Krebs cycle occur

Answer 6

In mitochondrial matrix

Question 7

Driver of Krebs cycle

Answer 7

Acetyl CoA

Question 8

Krebs cycle

Answer 8

Acetyl CoA combines with Oxaloacetate to create Citrate

8 further steps occur in cycle producing:
- 2 CO2
- 1 ATP
- 3 NADH
- 1 FADH2

(Uses O2, hence aerobic)

Question 9

Source of Acetyl CoA

Answer 9

Carbohydrates broken down into monosaccharides (e.g. glucose, fructose)

Proteins broken down into amino acids

Fats (triglycerides) broken down into Glycerol + Free fatty acids

Glucose, Amino acids and Glycerol can all be converted into Pyruvate

Pyruvate is converted into Acetyl CoA

Question 10

Glycolysis definition

Answer 10

Conversion of glucose to pyruvate

Occurs in cell cytoplasm

Question 11

Process of Glycolysis

Answer 11

Glucose activated by phosphorylation to form Glucose-6-Phosphate (G-6-P) - this requires ATP

Through series of 10 enzymatic reactions, 1 molecule of glucose is metabolised to form 2 molecules of pyruvate

2 molecules of NADH and 2 molecules of ATP are also formed per glucose molecule during glycolysis

Glycerol also enters this pathway to also be converted to pyruvate

Question 12

Role of amino acids in Krebs cycle

Answer 12

Amino acids can be converted into pyruvate, which is then converted to Acetyl CoA and drives the Krebs cycle

Amino acids can also directly enter the Krebs cycle via intermediate molecules

Question 13

Beta oxidation definition

Answer 13

Process by which free fatty acids are converted directly into Acetyl CoA

Occurs in Mitochondrion

Question 14

By-product of free fatty acid metabolism by Beta Oxidation

Answer 14

Ketoacid

Ketoacid can gain access into the Krebs cycle directly

Question 15

Net ATP molecule yield from one glucose molecule being fully metabolised via Krebs cycle by aerobic metabolism

Answer 15

Total 38 ATP

Question 16

4 steps in anaerobic metabolism

Answer 16

1) Glucose still converted to 2 pyruvate molecules, requiring 2 ATP

2) Pyruvate can’t be further metabolised to Acetyl CoA so doesn’t enter Krebs cycle

3) Each Pyruvate is converted to Lactate instead (yields net of 2 ATP total)

4) Once aerobic conditions are restored, Lactate transported to liver where it is converted back to Glucose by the process called Cori cycle

Question 17

3 phases of metabolic changes during starvation

Answer 17

First 24 hours

24 hours to 4 days

4 days onwards

Question 18

Metabolic changes during First 24 hours of starvation

Answer 18

As glucose levels fall, glycogen stores are mobilised (glycogenolysis)
This maintains a basal plasma glucose concentration

Glycogen stores are exhausted within 24 hours

Question 19

Metabolic changes from 24 hours to 4 days of starvation

Answer 19

Pyruvate generated from amino acids (protein breakdown) and glycerol (fat metabolism)

Pyruvate can be converted back into glucose so this maintains basal plasma glucose levels once glycogen stores are depleted

Question 20

Metabolic changes from 4 days onwards of starvation

Answer 20

Body switches to predominately fat metabolism to preserve its protein for essential body maintenance

Ketoacids from FFA metabolism used to drive Krebs cycle as an alternative to glucose

This ketoadaptation is relatively slow process as it is hormone dependent (e.g. cortisol and GH)

Question 21

Body areas which still require glucose as primary energy substrate during starvation

Answer 21

Erythrocytes

Renal medulla

50% of CNS

Question 22

How does death occur during starvation

Answer 22

Fat stores eventually depleted

Then protein breakdown increases and death follows

Question 23

Source of glycogen stores

Answer 23

Liver
Muscle

Question 24

Effect of starvation on Nitrogen balance

Answer 24

Starvation results in negative nitrogen balance

More nitrogen is excreted in urine during starvation