Bioenergetics 4 : Citric Acid cycle

Question 1

Where does CAC take place

Answer 1

The matrix of the mitochondria or cytosol of bacteria

Question 2

What is endosymbiosis (relating to mitochondria)

Answer 2

Mitochondria may have been originally bacteria that was taken up by a Eukaryotic cell.

Question 3

What is the benefits of Endosymbiosis

Answer 3

Mitochondria permit an existence with oxygen which is toxic.
SA increasing Cristae increase the cell capacity to make ATP, allowing larger cells.
As there is more ATP, allows more complex genomes as DNA is made from ATP. Allows more complex makes diversification.

Question 4

What allosterically activates PDH and what negative feedbacks it

Answer 4

Pyruvate, AMP, NAD, Ca2 + (signal that cells are depolarised-need ATP).
Negative feedback is AcetylcoA

Question 5

Step 1 of CAC

Answer 5

1. Citrate synthase makes Citrate from adding Acetyl CoA (2) and Oxaloacetate (4)

Question 6

Step 2 of CAC

Answer 6

Aconitase prepares the molecule for an oxidation reaction by moving around the OH group by removing water

Question 7

Step 3 of CAC

Answer 7

Isocitrate dehydrogenase removes CO2 which goes to the breath and the H+ are removed to make NADH

Question 8

Step 4 of CAC

Answer 8

Alpha ketoglutarate dehydrogenase removes a CO2 and reduces an NAD+. It adds a coenzyme A group Coa-SH to a-ketoglutarate

Question 9

What enzymes does Arsenic affect in the CAC and how does it work

Answer 9

The a-ketoglutarate dehydrogenase and pyruvate dehydrogenase are very similar
Arsenic affects both of them by binds to the lysine lipoamide which prevents it from adding an coenzyme A

Question 10

Compare the structure of enzymes in PDH and aKDH

Answer 10

E1: PDH uses Pyruvate and aKDH uses a-ketoglutarate but both make CO2
E2: PDH and aKDH both add CoA-SH but PDH makes Acetyl-CoA whereas aKDH makes Succinyl CoA.
E3: Both reduce NAD+ to NADH + H+

Question 11

Step 5 of CAC

Answer 11

Succinyl CoA synthetase or succinyl thiokinase. Removes the CoA, using the power of it to make an ATP or GTP -depending on the tissue. This is a substrate phosphorylation.

Question 12

Step 6 of CAC

Answer 12

Succinate Dehydrogenase/ Complex 2 of ETC and it is the only part of the CAC that . Accepts succinate and oxidases it to fumarate. It then reduces FAD to FADH. The electrons are transferred through iron cluster and heme.

Question 13

Step 7 of CAC

Answer 13

Fumarase adds wate to fumarate and this produces Malate.

Question 14

Step 8 of CAC

Answer 14

Malate dehydrogenase has then oxidises Malate and reduces another NADH

Question 15

How many pyruvate per glucose

Answer 15

2

Question 16

What are the three checkpoints controlling the CAC and what inhibits or activates it

Answer 16

PDH, IsocitrateDH and a-ketoglutarateDH are all inhibited by ATP and NADH.
For PDH it is also inhibited by its product acetyl coA.
and For KDH it is inhibited by its product Succinyl coA -> bc it runs out of CoA
For IDH it is activated by ADP

Question 17

What is the ratio of ADP/ATP that activates and inhibits IDH

Answer 17

Activates ADP:ATP= 10: 2

Deactivate ADP: ATP = 2:10

Question 18

How does [Ca2+] in muscle regulate IDH

Answer 18

When there is a lot of contractions, Ca2+ goes up and there is a need for more ATP so it makes it go faster

Question 19

What happens to the intermediates of CAC if one enzyme at one point is non functional?

Answer 19

The intermediates before the inhibition build up while the others after start to run out

Question 20

Summarise the conversion of Pyruvate to acetyl coA in oxidative decarboxylation reaction

Answer 20

Pyruvate from glycolysis has
1. A CO2 taken off
2. A coenzyme A is added
3 A NAD+ reduced

Question 21

What can be converted to acetyl CoA and what cannot be converted back

Answer 21

Pyruvate, fats, some amino acids. Fatty acids cannot be converted to glucose because this reaction has a high negative delta G and it is regulated. (irreversable)

Question 22

What are the products of the CAC per 1 acetyl coA

Answer 22

2 x CO2, FADH2 and 3NADH + 1 ATP or GTP

Question 23

How was CAC discovered

Answer 23

Hans Kreb who escaped from nazi germany during WWII. He observed that specific metabolites/intermediates increased respiration or accumulated when poisons were added. He radio labelled acetate (2Cs) that went in yet the 2CO2s that came out were different

Question 24

How does the 3 enzyme parts of pyruvate dehydrogenase oxidise pyruvate

Answer 24

Pyruvate binds to the ThiaminePP in E1 complex leaving acetate. Acetate is then moved to lysine lipoamide on E2. Coenzyme A is joined to acetate. This reduces the lysine lipoamide and this means that the FAD in E3 will accept it. It then transfers it to the NAD to reduce it

Question 25

What is the substrate level phosphorylation reaction in CAC and what does it make

Answer 25

Step 5 using Succinyl coA synthetase. When CoA-SH is released, the energy from this is used to add Pi to either ADP in muscle or GDP in the liver

Question 26

What is the product of 1 pyruvate oxidation to acetyl coA

Answer 26

1 CO2, 1 NADH

Question 27

What does it mean by CAC is amphibolic

Answer 27

Its both cata or anabolic. For anabolic reactions

0. Acetyl coA-> acetylcholine
1. Citrate -> fatty acids
2. A-ketoglutarate-> glutamate
3. Succinyl CoA-> porphyrin found in haemoglobin, cytochromes and chlorophyll
4. Malate-> glucose for
5. Oxaloacetate-> amino acid synthesis

Question 28

What are the 4 oxidation reactions in CAC

Answer 28

Step 3: Isocitrate -> A-ketoglutarate
Step 4: A-ketoglutarate -> Succinyl CoA
Step 6: Succinate -> Fumarate (FADH2)
Step 8: Malate -> Oxaloacetate

Question 29

What is the substrate phosphorylation reaction in CAC

Answer 29

Step 5 Succinyl CoA –> Succinate (removes the Coa group provides energy for substrate phosphorylation)

Question 30

What is the difference between FAD and NADH

Answer 30

NAD+ is mobile in aqueous environment and accepts 2 electrons in a single step where as FAD which accepts single electrons is bound within enzymes and so has less reducing power.

Question 31

What is a coenzyme and what is the 3 in the CAC

Answer 31

Complex organic structure that participates in enzymatic reactions. In CAC Co-enzyme A. NAD+ and FAD-> redox electron acceptors