the process of anaerobic respiration in eukaryotes

Question 1

what happens in respiration when oxygen is absent?

Answer 1

• oxygen cannot as the final electron acceptor at the end of oxidative photophosphorylation, protons are not able to combine with electrons and oxygen to form water
• concentration of protons increases in the matrix and reduces the proton gradient across the inner mitochondrial matrix
• reduced NAD and reduced FAD are not able to unload their hydrogen atoms and cannot be reoxidised
• Krebs cycle and link reaction stops

Question 2

where does lactate fermentation take place?

Answer 2

in mammalian muscle tissue during vigorous activity
in cells it happens in the cytoplasm

Question 3

what enzyme is used in lactate fermentation?

Answer 3

lactate dehydrogenase

Question 4

what is the lactate fermentation pathway?

Answer 4

pyruvate (made in glycolysis) accepts hydrogen atoms from reduced NAD (made in glycolysis)
catalysed by lactate dehydrogenase
pyruvate is reduced to lactate
reduced NAD becomes reoxidised to NAD which can then accept more hydrogen atoms from TP during glycolysis so glycolysis can continue

Question 5

where does the lactate move to ?

Answer 5

to the liver in the bloodstream

Question 6

what happens to lactate in the presence of more oxygen?

Answer 6

• lactate is converted to pyruvate which may enter the Krebs cycle via the link reaction
• lactate is recycled to glucose and glycogen

Question 7

what type of organisms use the ethanol fermentation pathway?

Answer 7

fungi such as yeast and plants

Question 8

where does ethanol fermentation take place?

Answer 8

cytoplasm

Question 9

what is ethanol fermentation also known as?

Answer 9

alcoholic fermentation

Question 10

what enzymes catalyse ethanol fermentation?

Answer 10

pyruvate decarboxylase and ethanol dehydrogenase

Question 11

what happens in the ethanol fermentation pathway?

Answer 11

pyruvate is decarboxylated and converted to ethanal - this is catalysed by pyruvate dehydrogenase
ethanal accepts hydrogen atoms from reduced NAD so becomes ethanol - ethanol dehydrogenase catalyses this reaction
reduced NAD is re-oxidised and made available to accept more hydrogen atoms from TP so allowing glycolysis to continue.

Question 12

which coenzyme is bound to pyruvate decarboxylase?

Answer 12

thiamine diphosphate

Question 13

what is the ATP yield from anaerobic respiration?

Answer 13

neither pathways produce any ATP but they allow glycolysis to continue so the net gain of 2 ATP per molecule of glucose is still obtained

Question 14

how does the ATP yield differ from aerobic respiration?

Answer 14

ATP produced from anaerobic respiration is about 1/15 of that produced during aerobic respiration