21: Respiration Flashcards
Linked reaction
Site: Mitochondrial matrix
- Each pyruvate molecule loses one molecule of carbon dioxide and one hydrogen atom
- The hydrogen atom is accepted by NAD to form NADH
- The remaining acetyl group combines with Coenzyme A to form Acetyl-CoA (carries the acetyl group into the Krebs cycle)
Describe the process of glycolysis.
- Site: Cytoplasm
- Glycolysis is catalysed by enzymes and does not require oxygen
- 1 molecule of glucose is activated by phosphorylation using 2ATP and broken down to 2 molecules of triose phosphate
- Each molecule of triose phosphate loses one hydrogen atom to form pyruvate. The energy released during the process is used to form 4 ATP, resulting in a net gain of 2 ATP. The hydrogen atom is accpeted by NAD to form NADH.
Role of Coenzyme A
- carrier molecule
- carries the acetyl group into the Krebs cycle
Krebs cycle
1. Formation of 6-C compound
Acetyl-CoA combines with another 4-C compound to form a 6-C compound. Coenzyme A is released.
Coenzyme A is regenerated and it can carry other acetyl groups formed from pyruvate in glycolysis into the Krebs cycle.
2. Regeneration of the 4-C compound
The 6-c compound is oxidised stepwise to regenerate the 4-C compound. Each of the reactions is catalysed by a different enzyme.
Each 6-C compound loses:
- 2 carbon dioxide molecules
- 4 hydrogen atoms (accpeted by 3NAD to form 3NADH and FAD to form FADH respectively)
- 1 ATP is directly formed by the energy released from the conversion
What will happen to pyruvate if Krebs cycle is inhibited?
- Pyruvate will not be metabolized
- However, the rate of glycolysis remains unchanged and the rate of oxidation of TP to pyruvate remains unchanged
- Hence, pyruvate accumulates
Oxidative phosphorylation
Site: mitochondrial inner membrane
- NADH and FADH are oxidised to regenerate NAD and FAD by losing hydrogen
- the hydrogen atom dissociates into hydrogen ions and electrons
- the electrons are accepted by electron accpetors and are passed down an ETC
- the electrons take part in redox reactions along the ETC catalysed by enzymes embedded in the inner membrane of mitochondria.
- energy released in the reactions: used to form ATP
- oxygen, final hydrogen and electron acceptor, combines to form water
Significance of oxygen as the final hydrogen and electron acceptor
Final hydrogen acceptor
- NAD and FAD can be regenerated
- so they can act as oxidising agent again to accept hydrogen atoms in glycolysis, linked reaction and Krebs cycle again
Final electron acceptor
- the electrons from the oxidation of NADH and FADH can be passed along the ETC
- releasing energy to form ATP again
Explain why the ETC cannot operate under anaerobic conditions.
- Without oxygen, which acts as the final electron acceptor of the ETC, electrons released from the oxidation of NADH and FADH cannot go through the ETC
- Oxidative phosphorylation stops
Explain why NAD and FAD cannot be regenerated without the presence of oxygen in aerobic respiration
- Without oxygen, which acts as the final electron acceptor of the ETC, electrons released from the oxidation of NADH and FADH cannot go through the ETC
- Oxidative phosphorylation stops
- NADH and FADH cannot be reduced
Significance of lactic acid fermentation
- maximum rate of aerobic respiration
- insufficient oxygen supply for complete oxidation of glucose in muscles
- lactic acid fermentation provides additional energy in a short period of time
- muscles can contract more powerfully at a higher rate
Removal of the lactic acid produced
- (20%) Lactic acid is converted into pyruvate and converted toAcetyl-CoA in linked reaction, enters Krebs cycle
- (80%) Additional amount of energy: convert lactic acid to glycogen for storage
Oxygen debt
- After exercise, breathing rate increases
- More oxygen, more NAD generated to oxidise lactic acid to pyruvate
- Additional amount of oxygen required to remove all lactic acid: oxygen debt
