5.7.6 anaerobic respiration in eukaryotes

Question 1

what happens to aerobic respiration if oxygen isn’t present

Answer 1

1. oxygen cannot act as final electron acceptor at end of oxidative phosphorylation - protons can’t combine with electrons/oxygen to form water
2. proton concentration increases in matrix & reduces protein gradient across cristae
3. oxidative phosphorylation stops
4. NADH & FADH cannot unload hydrogen atoms & can’t be reoxidised
5. krebs cycle & link reaction stops

Question 2

2 metabolic pathways used by eukaryotic cells to reoxidise NADH

Answer 2

• fungi (eg. yeast) & plant use ethanol fermentation pathway
• mammals use lactate fermentation pathway

Question 3

where does ethanol & lactate fermentation pathways take place

Answer 3

cytoplasm of cells

Question 4

3 steps of ethanol fermentation pathway

Answer 4

1. each pyruvate molecule produced in glycolysis is decarboxylated & converted to ethanal
   - catalysed by pyruvate decarboxylase, with coenzyme (thiamine diphosphate) bound
2. ethanal accepts hydrogen atoms from NADH, becoming reduced to ethanol
   - catalysed by ethanol dehydrogenase
3. NADH reoxidised & made available to accept more hydrogen atoms from triose phosphate = allows glycolysis to continue

Question 5

name 2 steps involved in lactate fermentation pathway

Answer 5

1. pyruvate (from glycolysis) accepts hydrogen atoms from NADH
   - catalysed by lactate dehydrogenase
   - 2 outcomes: pyruvate reduced to lactate & NADH becomes reoxidised
2. NADH can accept more hydrogen atoms from triose phosphate during glycolysis = glycolysis can continue

Question 6

what happens to the lactate produced by the lactate fermentation pathway

Answer 6

• carried from muscle tissue (in blood) to liver
• when more oxygen available, the lactate is either:
  1) converted to pyruvate (enter krebs cycle via link reaction)
  2) recycled to glucose & glycogen

Question 7

what would happen if lactate wasn’t removed from muscle tissue

Answer 7

pH lowered = inhibits action of many enzymes involved in glycolysis & muscle contraction

Question 8

net gain of ATP from anaerobic respiration

Answer 8

2 ATP per glucose molecule (glycolysis)