Tricarboxylic Acid Cycle, Electron Transport Chain & ATP Synthesis

Question 1

Where does the TCA cycle occur?

Answer 1

in the matrix of the mitochondria

Question 2

Once pyruvate is produced, what happens?

Answer 2

It is transported into the mitochondria converted into acetyl CoA and enters into the TCA cycle

Question 3

What is the reaction converting pyruvate to acetyl-CoA?

Answer 3

CO2^- S-CoA
I I
C=O + HS-CoA + NAD+ => C=O +CO2+NADH
I coenzyme I
CH3. CH3

pyruvate AcetylCoA

Question 4

What enzyme is required in this reaction (pyruvate to CoA)? Is it thermodynamically favourable? Is it reversible?

Answer 4

pyruvate deH2ase
highly thermodynamically favourable
no

Question 5

What is the TCA cycle?

Answer 5

the process by which the acetyl group is oxidatively decarboxylated to produce CO2, NADH and ubiquinol

Question 6

What is the role of Coenzyme A?

Answer 6

activates acetyl groups so they can be readily transferred to metabolites

Question 7

What are the three enzymes found in the pyruvate dehydrogenase complex and what are their roles?

Answer 7

E1 pyruvate dehydrogenase= oxidative carboxylation of pyruvate
E2 dihydrolipoyl transacetylase= transfer of acetyl group to CoA
E3 dihydrolipoyl dehydrogenase= regeneration of lost lipoamide

Question 8

What is the structure of pyruvate dehydrogenase?

Answer 8

• inner core =copies of E2 and E3

- outer shell = copies of E1 and E2

Question 9

What is the order of the carbon containing molecules in the TCA cycle?

Answer 9

Acetyl CoA (C2)
citrate (C6)
cis-aconiatate (C6)
isocitrate (C6)
α-keto glutarate (C5)
succinyl-CoA (C4)
succinate (C4)
fumigate (C4)
malate (C4)
oxalo-acetate (C4)

Question 10

What are the overall reactions of the TCA cycle?

Answer 10

Acetyl CoA => CoA + 2CO2
3NAD+ => 3NADH
FAD => FADH2
GDP + Pi => GTP (substrate level phosphorylation)

Question 11

What is the equation for Gibbs free energy of electron transfer?

Answer 11

ΔG = -nF ΔEh

n=no. of electrons
F= faraday’s constant = 96500C.mol^-1

ΔEh must be positive for a spontaneous reaction

Question 12

Does PH alter mid-point potentials?

Answer 12

yes

Question 13

When does Eh =Em

Answer 13

when [red] = [ox]

Question 14

What are the steps of oxidative phosphorylation?

Answer 14

1. NADH is oxidised to NAD+ and the 2 electrons pass down complex I where they meet ubquinone
2. ubiquinone is reduced to ubiquinol
3. ubiquinol carries electrons to complex III
4. electrons flow through complex III to cytochrome C
5. cytochrome C carries electrons to complex IV which reduces complex IV and the electrons are transferred to oxygen (terminal electron acceptor)

Question 15

What is the energy used for that is released from these electron transfer events?

Answer 15

to pump protons (for every 2 electrons that flow through complex I, 4 protons are pumped from the matrix to the outside (overall 10 protons pumped across per 2 electrons) to create a PH and charge gradient

Question 16

What is the reduced form of pyruvate?

Answer 16

lactate

Question 17

What is the oxidised form of succinate?

Answer 17

fumigate

Question 18

What is complex II also known as?

Answer 18

mitochondrial succinate dehydrogenase

Question 19

What is the only membrane-bound enzyme in the TCA cycle?

Answer 19

mitochondrial succinate dehydrogenase

Question 20

What is complex II part of?

Answer 20

ETC and TCA cycle (catalyses succinate turning into fumerate)

Question 21

What stops the TCA cycle if ATP is not required?

Answer 21

complex II

Question 22

what is an alternate route into the TCA?

Answer 22

complex II (lower energy entry) every time succinate is being converted into fumigate in the TCA 2 electrons enter the TCA cycle via complex II

Question 23

If you stop ATP synthesis using oligomyocin what do you also stop?

Answer 23

ETC

Question 24

How do uncouplers work?

Answer 24

by increasing the permeability of the membrane to protons

Question 25

What are the effects of an uncoupler?

Answer 25

-relief from respiratory control: acceleration of respiratory rate and inhibition of ATP synthesis

Question 26

What is the ΔG equation for ions?

Answer 26

ΔG = -mF Δp

m= amount of charge (no. of ions xF)
F=faraday constant
Δp= electrochemical potential across the membrane

Question 27

What is the structure of ATP synthase?

Answer 27

made up of stator and rotor

Question 28

What is the yeast F0 rotor formed of?

Answer 28

10 helical hairpin proteins

-on the outside helix of each hairpin an aspartic acid which spins the ATP synthase

Question 29

What happens when a proton moves through ATP synthase?

Answer 29

1. protein moves halfway across the membrane where it meets an aspartic acid on the C ring, the only way the proton can get through is by turning the wheel by neutralising the aspartic acid so it can move through the lipid bilayer and when the aspartic acid reaches the channel again it releases the proton so it can travel through the channel

Question 30

What happens when the C ring spins around?

Answer 30

It drives the gamma subunit to spin around, catalysing the unfavourable reaction of ATP synthesis

Question 31

How does ATP get synthesised?

Answer 31

• there are 3 active sites in ATP synthase, one has ATP bound, one has ADP and Pi bound and the other is empty
• ADP and Pi bind to empty active site
• gamma subunit rotates, activating ADP and Pi
• gamma subunit rotates further and unbinds already formed ATP

Question 32

How many ATP are produced for each 360 degree rotation of the gamma subunit?

Answer 32

3