eLFH - Metabolism Physiology Part 1 Flashcards
Oxidative phosphorylation definition
Process by which Adenosine Triphosphate (ATP) is produced by ATP synthetase
Requirement for oxidative phosphorylation to occur
Flow of H+ ions through ATP synthetase
Location of ATP synthetase
Mitochondrial membrane
How does mitochondrion source H+ ions
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
Source of NADH and FADH2
Krebs cycle
aka Tricarboxylic acid cycle
aka Citric acid cycle
Where does Krebs cycle occur
In mitochondrial matrix
Driver of Krebs cycle
Acetyl CoA
Krebs cycle
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)
Source of Acetyl CoA
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
Glycolysis definition
Conversion of glucose to pyruvate
Occurs in cell cytoplasm
Process of Glycolysis
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
Role of amino acids in Krebs cycle
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
Beta oxidation definition
Process by which free fatty acids are converted directly into Acetyl CoA
Occurs in Mitochondrion
By-product of free fatty acid metabolism by Beta Oxidation
Ketoacid
Ketoacid can gain access into the Krebs cycle directly
Net ATP molecule yield from one glucose molecule being fully metabolised via Krebs cycle by aerobic metabolism
Total 38 ATP
4 steps in anaerobic metabolism
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
3 phases of metabolic changes during starvation
First 24 hours
24 hours to 4 days
4 days onwards
Metabolic changes during First 24 hours of starvation
As glucose levels fall, glycogen stores are mobilised (glycogenolysis)
This maintains a basal plasma glucose concentration
Glycogen stores are exhausted within 24 hours
Metabolic changes from 24 hours to 4 days of starvation
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
Metabolic changes from 4 days onwards of starvation
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)
Body areas which still require glucose as primary energy substrate during starvation
Erythrocytes
Renal medulla
50% of CNS
How does death occur during starvation
Fat stores eventually depleted
Then protein breakdown increases and death follows
Source of glycogen stores
Liver
Muscle
Effect of starvation on Nitrogen balance
Starvation results in negative nitrogen balance
More nitrogen is excreted in urine during starvation