Pyruvate Oxidation and Krebs Cycle

Question 1

How does pyruvate move from the cytosol into the mitochondrial matrix?

Answer 1

Through secondary active transport

Question 2

What are the products of pyruvate oxidation?

Answer 2

For each pyruvate molecule:
- 1 CO2 caused by decarboxylation by pyruvate dehydrogenase
- 1 NADH
1 acetyl coa with 2 carbons (later binds to coenzyme A which goes to krebs cycle)

Question 3

Where does pyruvate oxidation occur in prokaryotes

Answer 3

Cytosol

Question 4

What are the products of the krebs cycle?

Answer 4

2 Co2, 3 NADH, 1 FADH2, 1 ATP, 3H+, 1 CoA

Question 5

Segment A

Answer 5

Pyruvate from glycolysis is oxidized into an acetyl group that feeds into the citric acid cycle; 2-C acetyl group combines with 4-C oxaloacetate to produce 6-C citric acid compound

Question 6

Segment B

Answer 6

Oxidation reactions produce NADH; loss of two CO2’s leaves a new 4-C compound and 1 ATP is generated for each acetyl group

Question 7

Segment C

Answer 7

Two additional oxidations generate an NADH and an FADH2 and regenerate oxaloacetate

Question 8

Step 1

Answer 8

Condensation: A 2-carbon acetyl group carried by CoA is transferred to oxaloacetate, forming citrate
- 1 molecule of water is used
Enzyme: Citrate synthase
Substrate: oxaloacetate
Product: citrate

Question 9

Step 2

Answer 9

Isomerization: Citrate is rearranged into its isomer, isocitrate
Enzyme: Aconitase
Substrate: Citrate, product: isocitrate

Question 10

Step 3

Answer 10

First oxidization: Isocitrate is oxidized to alpha-ketoglutarate and one carbon is lost as CO2 and NAD+ is reduced to NADH and H+ so only 5 C remaining
Enzyme: Isocitrate dehydrogenase
Substrate: Isocitrate, product is alpha-ketoglutarate

Question 11

Step 4

Answer 11

Second oxidization: Alpha-ketoglutarate is oxidized to succinyl Co-A and one C is released as CO2, and NaD+ is reduced to NADH and H+
Enzyme: ketoglutarate dehydrogenase
Substrate: alpha-ketoglutarate
Product: succinyl coA
One CO2 is lost, NaD+ is reduced to NADH+H+ and 4 Carbons remain

Question 12

Step 5

Answer 12

Substrate Level Phosphorylation: CoA is released from succinate and this gives GDP the energy to turn into GTP, which in turn allows ADP to turn into ATP via substrate level phosphorylation. This is the only ATP made in the citric acid cycle
Enzyme: succinyl CoA synthetase
Substrate: succinyl coA
Product: Succinate and ATP
This is the only molecule made in the citric acid cycle

Question 13

Step 6

Answer 13

Succinate is oxidized to fumarate, and the two electrons and protons removed are transferred to FAD to form FADH2
Enzyme: succinate dehydrogenase
Substrate: Succinate
Product: Fumarate

Question 14

Step 7

Answer 14

Fumarate is converted into malate by the addition of a molecule of water
Enzyme: Fumarase
Substrate: Fumarate
Product: Malate (4C)

Question 15

Step 8

Answer 15

Malate is oxidized to oxaloacetate, reducing NAD+ into NADH + H+
Oxaloacetate can react with acetly-CoA to reenter the cycle

Question 16

By the end of the krebs cycle, what products do we have?

Answer 16

6 CO2: 2 co2 in pyruvate oxidation, 4 co2 in krebs cycle (step 3, isocitrate dehydrogenase and step 4, ketoglutarate dehydrogenase)

4 ATP: 2 from glycolysis (step 10, pyruvate kinase), 2 from krebs (step 5, succinyl Coa synthetase)

10 NADH- 6 from krebs (step 3,4,8, isocitrate, ketoglutarate, malate dehydrogenase), 2 from pyruvate oxidation, 2 from glycolysis (step 6, triose phosphate dehydrogenase)

2 FADH2- 2 from krebs step 6 (succinate dehydrogenase)