MCBG S18 TCA And Oxidative Phosphorylation

Question 1

What happens to pyruvate before it enters the TCA?

What is the overall reaction and what is it catalysed by?

Is it a reversible reaction?

Answer 1

• Link reaction - converted to Acetyl CoA.

Pyruvate + CoA + NAD+ -> AcetylCoA + NADH + H+ + CO2

Irreversible key regulatory step.

Question 2

PDH is a ____________ complex consisting of _ enzymes the different enzymes have different ___________.

Answer 2

Multi-enzyme
5
Co-factors

Question 3

What are the cofactors within PDH provided by?

As a result what specific vitamin deficiency are PDH reactions sensitive to?

Answer 3

B vitamins

Vitamin B1 deficiency

Question 4

What is pyruvate dehydrogenase stimulated by?

Answer 4

Pyruvate 
CoA
NAD+
ADP
Dephosphorylation

Question 5

What is pyruvate dehydrogenase inhibited by?

Answer 5

Acetyl CoA 
NADH
ATP
Citrate
Phosphorylation

Question 6

Why can PDH deficiency (Vitamin b12 deficiency) result in lactic acidosis?

Answer 6

PDH needed for pyruvate to enter TCA without it its entry into TCA is restricted and therefore it enters Lactate production pathway.

Question 7

What is produced overall per molecule of glucose in the TCA?

Answer 7

6 NADH
2 FADH2
2 GTP
4CO2

Question 8

What are the 2 regulatory steps and there enzymes?

What stimulates both these enzymes and what inhibits them?

Answer 8

Isocitrate dehydrogenase and alpha-ketaglutarate.

ADP stimulates both.

NADH ATP inhibits Isocitrate dehydrogenase.
NADH ATP and succinyl CoA inhibits a-ketaglutarate dehydrogenase.

Question 9

What intermediates in TCA supply biosynthetic processes?

Answer 9

A-ketaglutarate, succinate, maltate and oxaloacetate - amino acids feed in and out.

Succinate - makes haem

Oxaloacetate - makes glucose

Citrate - makes fatty acids.

Question 10

What are 2 steps in Oxidative Phosphorylation?

Answer 10

Electron transport chain

ATP synthesis

Question 11

NADH and FADH2 transfer electrons to electron carrier proteins.

What is the purpose of this?

What proteins do NADH and FADH2 transfer there electrons to?

How many electrons do they each transfer?

Answer 11

Electron transfer releases energy used to pump H+ into intermembrane space.

NADH gives 2 electrons to NADH dehydrogenase aka complex 1.

FADH2 gives 2 electrons to coenzyme q.

Question 12

Why does FADH2 electron transfer lead to less ATP synthesis than NADH?

Answer 12

Coenzyme Q does not itself move protons into the intermembrane space, whereas complex I does.
This means that overall when the electrons travel through the PTC NADH electrons travel through 3 and FADH2’s electrons transfer through 2.
This means less H+ is pumped into the intermembrane space as a result of FADH2 electrons. Less ATP synthesis.

Question 13

What is another name for complex IV?

Which complexes are the PTCs?

What occurs at complex IV?

Answer 13

Cytochrome oxidase

I, III and IV

Oxygen combines with electrons and protons to becomes reduced to water.

Question 14

What is the fate of the protons from FADH2?

Answer 14

They join with electrons and oxygen at complex IV to form water.

Question 15

What does accumulation of the protons in the intermembrane space form?

What are these protons role in ATP synthesis?

Answer 15

Form an electrochemical gradient.

They move via chemiosmosis through ATP synthase into the matrix and the proton-motive force they generate drives phosphorylation of ADP to ATP.

Question 16

Describe how oxidative phosphorylation is regulated by [ATP].

The description should show how ATP synthase and electron transport are closely coupled.

Answer 16

When ATP:ADP ratio high there is no substrate for ATP synthase.
Inward flow of H+ stops.
[H+] in intermembrane space increased.
Prevents further H+ pumping by PTCs and as a result electron transport stops.

Question 17

What are some inhibitors of oxidative phosphorylation?

What do they do?

Answer 17

CO, CN

CN blocks electron transport by preventing acceptance of electrons by O2.

Question 18

What do uncouplers do?

What knock-on effect does this have on ATP synthesis?

Name 3 uncouplers.

Answer 18

They increase the permeability of the inner membrane to H+.

Dissipation of electrochemical/proton gradient, less proton motive force to dive ATP synthesis.

Dinitrophenol, dinitrocresol, fatty acids.

Question 19

How is UCP-1 aka thermogenin activated?

Answer 19

Sympathetically released NA will bind to B3 adrenoceptors which will eventually lead to PKA activating TAG lipase.
Fatty acids released by TAG lipase.
Fatty acids - B-oxidation NADH and FADH2 made which can enter electron transport.
Fatty acids activate UCP-1.

Question 20

How does UCP-1 enable non-shivering thermogenesis in BAT?

Answer 20

Increases permeability of inner membrane to H+ by transporting H+ ions back into matrix.
Means as proton are pumped by PTCs they return to matrix.
Energy from pumping is not used to synthesise ATP but is instead dissipated as heat.

Question 21

BAT is found in who?

Specifically where is BAT located?

Answer 21

In newborns and hibernating animals

Around vital organs.

Question 22

What is the difference between the proteins required in oxidative phosphorylation and substrate level?

Answer 22

OP needs membrane PTCs

SLP needs soluble enzymes

Question 23

What can be said about the coupling that occurs in OP compared to SLP?

Answer 23

OP indirect coupling through proton gradient generation

SLP direct coupling through high energy bond formation via phosphate transfer.

Question 24

OP and SLP don’t need O2 to work.

True or false?

Answer 24

False

OP aerobic

Question 25

Which one is the more vital process for ATP synthesis, OP or SLP?

Answer 25

OP lots of ATP made compared to SLP.