Respiration Flashcards
What are the stages of aerobic respiration ?
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
Why is O2 needed for aerobic respiration ?
O2 acts as the final electron acceptior at the end of the ETC, allowing the EC in the ETC to reoxidise.
Without O2, EC cannot reoxidise and oxidative phosphorylation cannot occur.
Oxidative phosphorylation uses H+ from NADH and FADH hence, NAD and FAD not regenerated and cannot be used for link reaction and Krebs cycle
What are the products of glycolysis ?
2 pyruvate
2 NADH
2 net ATP
Where does glycolysis occur ?
Cytoplasm
Outline glycolysis
Glucose enters the cell via facilitated diffusion
- Phosphorylated twice by PFK to form fructose-1,6-bisphosphate using energy form 2 ATP hydrolysis
- Fructose- 1,6-bisphosphate split into triose phosphate (TP)
- Each TP is oxidised by dehydrogenase, and electrons and protons released are donated to NAD forming NADH
- Inorganic phosphate added to TP forming 1,3- bisphosphoglycerate
- 1,3- bisphosphoglycerate dephosphorylsed into 3-phosphoglycerate (PGA) and again to form pyruvate. Each dephosphorylation uses energy form ATP hydrolysis, using 4 ATP
How does high levels of ATP inhibit PFK activity ?
ATP is both an alloestirc inhibitor and a substrate of PFK
At high ATP
Chance of ATP binding to the allosteric site of PFK is high, after binding, there is change in 3D conformation, active site no longer complementary to substrate and glycolysis is inhibited
What are the products of link reaction per glucose ?
2 CO2
2 Acetyl-coA
2NADH
Outline link reaction
Oxidative decarboxylation
- Pyruvate is decarboxylated via the removal of CO2 forming a 2C fragment
- 2C fragment oxidised by dehydrogenase, electrons and protons released donated to NAD forming NADH
- Coenzyme A added to form acetyl-coA
Where does link reaction occur ?
Mitochondrial matrix
What are the products form in Krebs cycle ?
6 NADH
2 FADH
2 ATP
4 CO2
Where does Krebs cycle occur ?
Mitochondrial matrix
Outline Krebs cycle
- Acetyl-coA accepted by oxaloacetate to form citrate
- Citrate undergo oxidative decarboxylation twice via CO2 removal , forming 2 NADH and 2 CO2
- Substrate level phosphorylation forms 1 ATP
- 2 oxidation reaction forms 1 NADH and 1 FADH regenerating oxaloacetate
Why is Krebs cycle a cycle ?
Oxaloacetate is regenerated and can combine with acetyl-coA again
Where does Oxidative phosphorylation occur ?
Cristae
Outline oxidative phosphorylation
NADH from glycolysis, link reaction, and Krebs cycle shuttle high energy electrons to the first electron carrier of the ETC releasing H+ into matrix
EC is reduced and passes electrons to the next EC along the ETC
EC is of progressively lower energy hence some energy is released at each transfer.
Energy is used to pump H+ from matrix into intermembrane space. Membrane is impermeable to H+ and H+ builds up forming proton gradient and PMF
H+ flows back into matrix via facilitated diffusion through the ATP synthase converting ADP + Pi into ATP via chemiosmosis
How does the ETC end ?
O2 acts as the final electron acceptor, combing with H+ to form H2O
Why is there only a small amount of NADH in the cell at any one time ?
NAD is always regenerated form NADH during oxidative phosphorylation when NADH shuttle high energy electrons to the first EC releasing H+ in the matrix
Approx what percentage of ATP is formed by oxidative phosphorylation ?
75%
How to calculate number of ATP formed ?
ATP generated + ATP from NADH/FADH
ATP from NADH
= no of. NADH x 2.5
ATP from FADH
= no of FADH x 1.5
Why does glycolysis still occur in absence of O2 ?
There is an alternative hydrogen acceptor
Plants: ethanal
Describe anaerobic respiration in plants
Pyruvate broken into ethanal in cytoplasm, catalysed by pyruvate decarboxylase
Ethanal serves as alternative hydrogen acceptor converted int ethanol, catalysed by alcohol dehydrogenase
Allows regeneration of NAD in cytoplasm for glycolysis to continue producing 2 net ATP for cellular activities
What are the substrate of PFK ?
ATP & fructose-6-bispospahte
