Oxidative Phosphorylation

Question 1

What happens to the electrons from glycolysis?

Answer 1

From one glucose molecule, the reactions of glycolysis, pyruvate dehydrogenase compex, the TC cycle produce: 10NADH + 10 H+ and 2 FADH2. Each one of these carries two high energy electrons

Question 2

What is oxidative phosphorylation?

Answer 2

The electrons from NADH and FADH2 are used to reduce 02 to H20. Their energy is used to pump protons from the mitochondrial matrix to the intermembrane space.
The protons flow back across the membrane following their conc gradient and the energy from proton flow will phosphorylate ADP to ATP

Question 3

What effect will pumping of protons across the membrane in the mitochondria have on the pH?

Answer 3

The pH of the intermembrane space will decrease - become more acidic and the will increase in the matrix - become more basic

Question 4

How does NADH from the cytoplasm get into the mitochondria?

Answer 4

During glycolysis, 2 NADH are formed in the cytoplasm but cannot cross the inner mitochondrial membrane and so the glycerol-3-phosphate and malate-aspartate will shuttle the NADH across the membrane

Question 5

What is the mechanism of the malate-aspartate shuttle?

Answer 5

NADH from glycolysis is used to generate malate from oxaloacetate in the cytosol. Malate transporters transfer malate to the matrix. Malate conversion to oxaloacetate in the TCA cycle generates NADH in addition to the malate that arises from fumarate

Question 6

In oxidative phosphorylation, what is the energy changed?

Answer 6

The electron transfer potential of NADH+ and FADH2 is converted into phosphoryl transfer potential of ATP

Question 7

How is phosphoryl transfer potential measured?

Answer 7

Free energy change for the hydrolysis of ATP

Question 8

How is the electron transfer potential measured?

Answer 8

Measured by the redox potential of a compound

Question 9

What is the redox potential of a compound?

Answer 9

A measure of how readily a reduced substance will donate an electron in comparison with H2

Question 10

What does a negative redox potential mean?

Answer 10

The reduced form of the substance has a lower affinity for electrons than H2

Question 11

What does a positive redox potential mean?

Answer 11

The reduced form of the substance has a higher affinity for electrons than H2

Question 12

What is the standard free energy change proportionally to?

Answer 12

The change in standard redox potential and the number of electrons transferred

Question 13

What does oxidative phosphorylation consist of?

Answer 13

Electron transport - electrons flow from NADH and FADH2 to O2. Flows along the respiratory chain, energy is used to pump H+ out of the mitochondrial matrix
ATP synthesis - electrochemical gradient of H+ across the mitochondrial inner membrane, energy stored in this gradient can be used to synthesise ATP

Question 14

What is the respiratory chain made up of?

Answer 14

Four multisubunit complexes in the inner mitochondrial space

Question 15

Where do electrons from NADH enter?

Answer 15

At complex 1

Question 16

Where do electrons from FADH2 enter?

Answer 16

Complex 2 which is part of the TCA cycle

Question 17

Where are electrons ultimately transferred to?

Answer 17

Onto O2 to form H2O - this is why we need to breathe oxygen

Question 18

What does coenzyme Q do?

Answer 18

Called Ubiquinone, hydrophobic that rapidly shuttles molecules within the membrane

Question 19

What is a cytochrome?

Answer 19

A protein which contains a haem group as a functional co-factor
Haem contains a Fe(2) ion which can take up and release electrons

Question 20

What does the H+ pump do?

Answer 20

Transfer of electrons through the respiratory chain is coupled with the transport of H+ ions from the matrix to the intermembrane space. 3 of the 4 respiratory complexes pump H+

Question 21

What is the electrochemical gradient?

Answer 21

There are more protons in the intermembrane space than the matrix and so this forms an electrical field with the matrix more negative. Protons therefore want to flow back into the matrix. This is coupled to ATP synthesis

Question 22

Where do protons flow?

Answer 22

Through the respiratory chain which pumps protons into the intermembrane space. These protons will flow back through ATP synthase. There are 2 separate proton pump systems

Question 23

What are the other names for ATP synthast?

Answer 23

Mitochondrial ATPase or F1F0ATPase

Question 24

What does the F1 subunit protrude into?

Answer 24

The mitochondrial matrix

Question 25

Where is the F0 subunit?

Answer 25

Is in a hydrophobic complex within the inner membrane, which contains the proton channel

Question 26

What forms the stator?

Answer 26

The a,b, alpha, beta and delta subunits

Question 27

What forms the rotor?

Answer 27

The c, gamma and epsilon subunits

Question 28

How does the rotor rotate?

Answer 28

The flow of protons turns the rotor and this conformational change leads to ATP synthesis

Question 29

How is oxidative phosphorylation inhibited?

Answer 29

It is inhibited at many stages. Cyanide, azide and carbon monoxide inhibit the transfer of electrons to oxygen
Can be inhibited by the lack of ability to form a proton gradient or the lack of ability to synthesise ATP

Question 30

What does oxidation of foodstuffs do?

Answer 30

Produces acetyl-CoA which produces ATP and releases electrons

Question 31

How are electrons transferred to the respiratory chain?

Answer 31

They are accepted by co-factors and transferred to the resp chain. This recycles the co-factors needed

Question 32

What is the P/O ratio?

Answer 32

A measurement of the coupling of ATP synthesis to electron transport. The number of molecules of inorganic phosphate incorporated into ATP per atom of oxygen used depends on the substrate which is oxidised.

Question 33

What does the ATP yield from the complete oxidation of one glucose molecule rely on?

Answer 33

The precise P/O ratio and which shuttle is used for transporting cytoplasmic NADH into the mitochondrial matrix