Lecture 8

Question 1

Compare the product yields of glucose catabolism and anabolism

Answer 1

Catabolism: 2ATP + 2NADH + 2pyruvate
Anabolism: 4ADP + 2GDP + glucose + 2NAD+

Question 2

What’s the yield of glucose 6-P catabolism?

Answer 2

2NADPH and maybe ribose-5P. Don’t need ribose 5-P to quench ROS or for reductive biosynthesis such as making fatty acids or sterols. You do need ribose 5-P when making NT, nucleic acids, and coenzymes.

Question 3

Compare the product yields between anaerobic and aerobic pyruvate catabolism

Answer 3

Anaerobic: lactate + (NAD+) OR EtOH + CO2 + (NAD+)

Aerobic: 3CO2 + 4NADH + 1FADH2 + 1GTP (TCA cycle)

Question 4

What are the 3 fates of pyruvate?

Answer 4

1. EtOH
2. Lactate
3. Acetyl-CoA

Question 5

Describe the process that goes on in the PDH complex

Answer 5

Pyruvate gives up a CO2 molecule at E1. TPP decarboxylates pyruvate to yield hydroxyethyl-TPP carbanion.

Lipoic acid in E2 accepts hydroxyethyl from TPP as an acetyl group. The oxidized lipoyllysine gets reduced into SH when hydroxyethyl bonds to it.
CoA substrate accepts acetyl group from lipoamide to form acetyl-CoA in E2.

In E3, FAD gets reduced to FADH2 by lipoamide
NAD+ gets reduced by FADH2 in E3

Question 6

What is the E1 enzyme in the PDH complex?

Answer 6

Pyruvate dehydrogenase

Question 7

What is the E2 enzyme in the PDH complex?

Answer 7

Dihydrolipoyl transacetylase

Question 8

What is the E3 enzyme in the PDH complex?

Answer 8

Dihydrolipoyl dehydrogenase

Question 9

Which 3 oxidative decarboxylations have the same coenzymes and mechanisms?

Answer 9

PDH complex
Alpha-ketoglutarate DH in TCA cycle
Alpha-keto acid DH in the oxidation of isoleucine

Question 10

Which are the same coenzymes for the 3 oxidative decarboxylations?

Answer 10

CoA and NAD+

Question 11

What are the products for each step in the TCA cycle?

Answer 11

Acetyl-CoA + OAA -> citrate -> isocitrate -> alpha-ketoglutarate -> succinyl-CoA -> succinate -> fumarate -> malate -> OAA

Officer, can I keep selling seashells for money?

Question 12

Which steps of the TCA cycle are key? Why?

Answer 12

The ones with DH because they’re irreversible

Steps 1, 3 ,4 ,6 and 8

Question 13

What is step 1 of the TCA cycle?

Answer 13

Acetyl-CoA + OAA -> citrate is irreversible, -deltaG

Question 14

What is step 3 of the TCA cycle?

Answer 14

Isocitrate decarboxylates to alpha-ketoglutarate. Generate NADH. Irreversible.

Question 15

What is step 4 of the TCA cycle?

Answer 15

Alpha-ketoglutarate gives up CO2 to become succinyl-CoA. Generating CO2 makes it irreversible.

Question 16

What is step 6 of the TCA cycle?

Answer 16

Succinate DH (Complex II!) generates FADH2

Question 17

What is step 8 of the TCA cycle?

Answer 17

Malate oxidizes NAD+ to make NADH. Malate converts to OAA

Question 18

Why can’t cells just oxidize acetate (acetyl-CoA) directly? Why so many steps?

Answer 18

The methyl group on acetyl-CoA cannot break off since we do not have the enzymes and cofactors needed to oxidize methane. However, methylene groups are readily oxidizable

Question 19

How many turns doe the TCA cycle go per glucose? Why?

Answer 19

2, because glucose splits into two pyruvates and each one gets processed in the cycle

Question 20

How many ATPs are made from 2 pyruvates?

Answer 20

30-32 ATP

Question 21

What is the purpose of anaplerotic pathways?

Answer 21

They replenish TCA cycle intermediates. They need OAA to pick up 2 carbons to guarantee that pyruvate is available.

Question 22

Which enzymes are involved in anaplerotic pathways?

Answer 22

Pyruvate carboxylase, PEP carboxylase, and Malic enzyme

First two make OAA. Last one makes malate and NADP+

Question 23

Reaction of Malic enzyme

Answer 23

Pyruvate + HCO3 + NADPH -> malate + (NADP+)