Citric Acid Cycle Big Picture

Question 1

how many C’s enter and as what?

Answer 1

2 carbons enter as acetyl CoA

Question 2

how many C’s leave and as what?

Answer 2

2 carbons leave as CO2, but not same C’s that entered

Question 3

how many GTP, FADH2, NADH formed?

Answer 3

1 GTP

1 FADH2

3 NADH (recycle FAD and NAD+ and e- harvested to provide E to make ATP)

Question 4

regulation

Answer 4

excess AMP/ADP activates (evolutionary advantage to make E when there is a lack via this signal)

excess Ca2+ activates (muscles release upon contraction so signals need more E)

excess ATP inhibits; evolutionary benefit to not make more E if it is in excess… make other biomolecules instead

Question 5

which enzymes are allosterically regulated?

Answer 5

oxaloacetate to citrate (claisen condensation 1)

isocitrate to alpha-ketoglutarate (oxidative decarboxylation 4)

alpha-ketoglutarate to succinyl-CoA (oxidative decarboxylation 5)

hint: arrows are single headed (committed steps)

Question 6

how did TCA evolve

Answer 6

under anaerobic conditions to provide biosynthetic precursors

in ancient microbes only needed to turn alpha-ketoglutarate into succinyl CoA to make TCA cycle vs. divergent pathway