PDH/TCA Cycle

Question 1

what is a metabolon?

Answer 1

complex of enzymes that carry out functionally related rxns, improves reaction rates

Question 2

how do metabolons provide advantages?

Answer 2

through substrate channeling (local substrate concentration can be high even if overall is low)

Question 3

what are the advantages of a metabolon?

Answer 3

allows intermediates to be transferred directly from one enzyme to another, minimizes diffusion of reactants

Question 4

what is the key role of PDH?

Answer 4

convert pyruvate into acetyl-CoA

Question 5

what is PDH made up of and where can you find it?

Answer 5

3 different enzymes tightly associated in one complex, located in mitochondria

Question 6

what is the PDH rxn step 1?

Answer 6

PDH + TPP carbanion of E1, product undergoes decarboxylation

Question 7

what is the PDH rxn step 2?

Answer 7

transferred by E1 to E2, redox rxn occurs

Question 8

what is the PDH rxn step 3?

Answer 8

acetyl group is transferred, produces acetyl-CoA

Question 9

what is the PDH rxn step 4?

Answer 9

E3 reoxidizes via transfer of 2e-

Question 10

what is the PDH rxn step 5?

Answer 10

E3 catalyzes e- transfer, is reoxidized to produce NADH

Question 11

what does TPP stand for?

Answer 11

thiamine pyrophosphate (1 of 5 cofactors used in PDH reaction)

Question 12

what is TPP responsible for?

Answer 12

PDH decarboxylation of pyruvate (forms carbanion on C atom which attacks pyruvate carbonyl C to form new C-C bond and release CO2)

Question 13

what is Beriberi?

Answer 13

disease associated with low thiamine levels, low levels reduce TPP and inhibit conversion of pyruvate (Wernicke-Korsakoff is neurological version of this)

Question 14

what does Beriberi result in?

Answer 14

slow mental rxns and reduced movement

Question 15

what does acetyl-CoA connect?

Answer 15

connects glycolysis (carbohydrate catabolism) and amino/fatty acid catabolism

Question 16

what occurs during stage 1 of the TCA cycle?

Answer 16

acetyl Co-A funnels many carbon sources into central pathway

Question 17

what occurs during stage 2 of the TCA cycle?

Answer 17

acetyl group is added to oxaloacetate to form citrate, other substrates can enter TCA through intermediates

Question 18

what is the energetic outcome of stage 2 of the TCA cycle?

Answer 18

reduction of 3 NADH and 1 FADH2, 1 ATP, and intermediates

Question 19

what occurs during stage 3 of the TCA cycle?

Answer 19

reduced electron carriers are oxidized to synthesize more ATP

Question 20

which TCA reaction is closest to the PDH rxn?

Answer 20

alpha-ketoglutarate dehydrogenase complex

Question 21

what is the glyoxylate cycle?

Answer 21

how plants convert fat into sugars

Question 22

what are the four anabolic pathways fueled by TCA?

Answer 22

citrate, alpha-ketoglutarate, succinyl-CoA, oxaloacetate

Question 23

what does the citrate anabolic pathway produce?

Answer 23

fatty acids, sterols

Question 24

what does the alpha-ketoglutarate anabolic pathway produce?

Answer 24

glutamate (other AAs, purines)

Question 25

what does the succinyl-CoA anabolic pathway produce?

Answer 25

heme, chlorophyll

Question 26

what does the oxaloacetate anabolic pathway produce?

Answer 26

aspartate (other AAs, purines and pyrimidines)

Question 27

what is the overall goal of the TCA cycle?

Answer 27

generate NADH, FADH2, ATP, and biosynthetic precursors for anabolic pathways