Citric Acid Cycle

Question 1

what are the 3 possible fates of pyruvate?

Answer 1

1. fatty acid synthesis
2. lactate
3. enter the citric acid cycle

Question 2

where does most pyruvate go and what happens to it as a result?

Answer 2

enters the citric acid cycle to be broken down to produce more ATP

Question 3

what is the citric acid cycle?

Answer 3

the breakdown of glucose, fat, and amino acids

Question 4

where does the citric acid cycle take place?

Answer 4

in the mitochondria

Question 5

in chemical terms, what is the citric acid cycle?

Answer 5

the oxidation of acetyl-CoA resulting in formation of ATP

Question 6

is the citric acid cycle anaerobic or aerobic? what does this mean?

Answer 6

it is aerobic, so there must be O2 present to activate the mitochondria for this to occur

Question 7

give the 8 cyclic steps of the citric acid cycle (including step 0)

Answer 7

0. pyruvate is converted to acetyl CoA by pyruvate dehydrogenase and the input of CoASH, the input conversion of NAD+ to NADH + H+, and the release of CO2
1. acetyl CoA combines with oxaloacetate and is converted to citrate by citrate synthase and the input of H2O and the release of CoASH
2. citrate is converted to isocitrate by aconitase
3. isocitrate is converted to alpha-ketoglutonate by isocitrate hydrogenase along with the input conversion of NAD+ to NADH + H+ and the release of CO2
4. alpha-ketoglutonate is converted to succinyl CoA by alpha-ketoglutonate dehydrogenase along with the input of CoASH, the input conversion of another NAD+ to NADH + H+, and the release of CO2
5. succinyl CoA is converted to succinate by succinyl CoA synthetase, along with the input conversion of an ADP + Pi to an ATP and the release of CoASH
6. succinate is converted to fumerate by succinate dehydrogenase and the input conversion of an FAD to an FADH2
7. fumerate is converted to malate by fumerase and the input of H2O
8. malate is converted back to oxaloacetate to restart the cycle by malate dehydrogenase and the input conversion od NAD+ to NADH + H+

Question 8

by what two enzymes is the citric acid cycle regulated?

Answer 8

1. pyruvate dehydrogenase

2. isocitrate dehydrogenase

Question 9

how does pyruvate dehydrogenase regulate the citric acid cycle?

Answer 9

is it activated by high concentrations of pyruvate (meaning high substrate availability)

Question 10

how does isocitrate dehydrogenase regulate the citric acid cycle?

Answer 10

it is inhibited by a high NADH + H+ to NAD+ ratio, so the buildup of energy reserves in the mitochondria puases the cycle to store as fat for later

Question 11

how much ATP is produced from the oxidation of two molecules of pyruvate by the citric acid cycle (from one glucose)?

Answer 11

1 pure ATP plus
4 NADH + H+ (x2.25) = 10 more ATP plus
one FADH2 (x1.5) = 1.5 ATP equals
12.5 ATP from one pyruvate so multiplied by 2 equals a total of 25 ATP from one glucose (2 pyruvates)

Question 12

how many total molecules of ATP can be produced from one glucose molecule?

Answer 12

25 from citric acid cycle plue the 7 from glycolysis equals 32 total ATP from one glucose