BIOC192 Lecture 30 - Acetyl CoA and The Citric Acid cycle

Question 1

what is acetyl CoA?

Answer 1

two carbon chains attached to a CoA molecule

Question 2

where does the citric acid cycle occur?

Answer 2

occurs in the mitochondria

Question 3

does the cycle finish with the same molecule it started with?

Answer 3

yes, the cycle starts and finish with the same molecule

Question 4

what happens when carbon enters and leaves the citric acid cycle?

Answer 4

• 2 carbons in acetyl-CoA in

- 2 carbons as carbon dioxide out (oxidation complete)

Question 5

what 3 molecules does the citric acid cycle use to capture energy?

Answer 5

• 1 ATP
• 3 NADH
• 1 FADH

Question 6

what are the two parts of the citric acid cycle?

Answer 6

1) release of carbon
2) regeneration of the starting molecule
- energy captured in both parts

Question 7

what occurs in the reaction of the condensation of acetyl-CoA with oxaloacetate?

Answer 7

2 carbons entering the citric acid cycle as acetyl-CoA is attached to 4 carbon oxaloacetate to produce 6 carbon citrate
-because this s a cycle the 2 carbons need to be removed

Question 8

where does the energy for the condensation reaction of acetyl-CoA with oxaloacetate come from?

Answer 8

comes from the hydrolysis of CoA from acetyl-CoA

Question 9

what occurs in the reaction of isomerisation of citrate?

Answer 9

rearrangement of citrate to isocitrate makes the molecule susceptible to decarboxylation
-catalysed by aconitase

Question 10

what is the relationship between targeting the citric acid cycle and killing animals?

Answer 10

both nature ad man have targeted the citric acid cycle as a way of killing animals

Question 11

what is the poison ‘1080’?

Answer 11

sodium fluroacetate

Question 12

what is fluroacetate metabolised too?

Answer 12

fluroacetate is metabolised to flurocitrate

Question 13

what are the two reaction steps of oxidative decarboxylation in the removal of the 1st carbon?

Answer 13

1) oxidation
2) decarboxylation
- both catalysed by isocitrate dehydrogenase
- energy captured in NADH

Question 14

what is the reaction of the removal of the 1st carbon?

Answer 14

an oxidative decarboxylation

Question 15

what is the reaction of the removal of the 2nd carbon?

Answer 15

a second oxidative decarboxylation

Question 16

what occurs in the oxidative decarboxylation in the removal of the 2nd carbon?

Answer 16

very similar to the pyruvate dehydrogenase reaction

-energy captured in NADH

Question 17

what occurs in summary in the first part of the citric acid cycle?

Answer 17

• 2 carbons are removed
• energy is conserved as NADH
• a 4 carbon molecule has been regenerated (succinyl-CoA)

Question 18

what is considered as the energy equivalent of ATP?

Answer 18

GTP

Question 19

what occurs in the succinyl-CoA to succinate reaction?

Answer 19

the conversion of succinyl-CoA to succinate is like the activation of fatty acids in reverse

• the removal of CoA releases enough energy to drive the synthesis of GTP
• 3rd substrate level phosphorylation

Question 20

what is substrate-level phosphorylation?

Answer 20

the direct use of energy foam substrate molecule to drive the synthesis of ATP (or equivalent)

Question 21

what occurs in the reaction from succinate to fumarate?

Answer 21

using succinate dehydrogenase a double bond carbon is formed with the donation of H+ from FAD to FADH2

Question 22

what occurs in the reaction from fumarate to malate?

Answer 22

using fumarate, H2O hydrates the double carbon bond to spilt to a single carbon bond

Question 23

what occurs in the reaction from malate to oxaloacetate?

Answer 23

using malate dehydrogenase he single carbon bond is converted to a double carbon bond through oxidation
-NAD to NADH, H+

Question 24

what is the overall reaction for the citric acid cycle?

Answer 24

acetyl-CoA + 3NAD+ + FAD + 2H2O + GDP + Pi –>2CO2 + CoASH + 3NADH + 3H+ + FADH2 + GTP