Oxidative Phosphorylation

Question 1

What do the reactions of glycolysis, pyruvate dehydrogenase complex, and the TCA cycle produce from one glucose molecule ?

Answer 1

10 NADH + 10 H+
2 FADH2

Each carries two high-energy electrons that can be used to generate ATP

Question 2

Describe electron movement from NADH and FADH2 in the electront transport chain

Answer 2

Electrons from NADH and FADH2 are used to reduce O2 to H2O

-Once re-oxidised in the electron transport chain they generate ATP and then can be reused to catabolise more glucose

Oxidised to NAD+ and FAD; organic co-factors

Question 3

How does NADH cross the inner mitochondrial membrane ?

Answer 3

Glycerol-3-phosphate and malate-aspartate shuttles
-These molecules cannot contribute to oxidative phosphorylation unless they enter the matrix.

Question 4

What is redox potential ?

Answer 4

The standard redox potential E’o of a (reduced) substance X is a measure for how readily X donates an electron in comparison with H2
-Aka reduction potential

Question 5

What does a positive and negative redox potential mean ?

Answer 5

A negative E’o means that the reduced form of X has a lower affinity for electrons than H2, a positive E’o means the opposite
-Negative E’o are stronger reducers and positive are stronger oxidisers (negative doesnt want electrons and positive does)

Question 6

What happens in In oxidative phosphorylation ?

Answer 6

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

Question 7

How are phosphoryl and electron transfer potentials measured ?

Answer 7

Phosphoryl transfer potential
-Measured by free energy change, DGo’ during ATP hydrolysis

Electron transfer potential
-Measured by the redox potential (or reduction potential), E’o, of a compound

delta is triangle

Question 8

What are the stages of oxidative phosphorylation ?

Answer 8

1) Electron transport
-Electrons flow from NADH and FADH2 to O2
-Respiratory chain
-Energy is used to pump H+ out of the mitochondrial matrix
2) ATP synthesis
-Electrochemical gradient of H+ across mitochondrial inner membrane
-Energy stored in this gradient can be used to synthesise ATP

This converts energy of electrons to energy of ATP

Question 9

How does oxidative phosphorylation work ?

Answer 9

1) Electrons from NADH and FADH2 are used to reduce O2 to H2O
2) Energy of electron transport is used to pump protons (H+) from mitochondrial matrix into intermembrane space
-pH decreases in intermembrane space, increases in the matrix
3) Protons flow back across the membrane through transporter linked to ATP synthase, following their concentration gradient
4) Energy of proton flow is used to phosphorylate ADP to ATP
5) Without O2 then Oxidative Phosphorylation stops.

Question 10

Describe the respiratory chain

Answer 10

Electrons handed down from carriers with increasingly positive redox potentials, transferred onto O2 to form H2O
-Oxygen is the final electron acceptor

Carriers are multisubunit complexes on innter mitochondrial membrane
-NADH electrons enter at complex I
-FADH2 eelctrons enter at complex II

Transfer of electrons through the respiratory chain is coupled to transport of H+ from the mitochondrial matrix to the intermembrane space

complex II is succinated dehydrogenase and has a role in TCA cycle

Question 11

What are cytochomes ?

Answer 11

Cytochromes are proteins which contain a haem group as a functional co-factor
-Haem contains an Fe(II) ion which can take up and release electrons
-cytochome C is a mobile electron carrier which moves electrons from complex III to IV, enabling final electron donation to 02

Question 12

Describe the steps of oxidative phosphorylation

Answer 12

1) Respiratory chain - electrons handed down from carriers with increasingly positive potentials, transferred onto O2 to form H2O
-Oxygen is the final electron acceptor
2) Transfer of electrons through respiratory chain is coupled to transport of H+ from the mitochondrial matrix
-electron transfer provides energy for H+ active transport
3) 1, 3 and 4 respiratory complexes pump H+ into the intermembrane space (3/4)
4) Flow of H+ back into the matrix through ATP synthases (following concentration gradient) phosphorylates ADP → ATP

Question 13

Describe the structure of ATP synthase

Answer 13

Contains F1 and F0 subunits

F1 subunit
-Protrudes into mitochondrial matrix

F0 subunit
-Is a hydrophobic complex in the inner membrane
-Contains the proton channel

F0 subunit and bottom of F1 forms the rotor
-Flow of protons turns the rotor
-Conformational changes lead to ATP synthesis

Most of F1 forms the stator

Question 14

Give examples of how the electron transport chain can be inhibited

Answer 14

Cyanide, azide, and CO inhibit transfer of electrons to O2
-no proton gradient can be formed
-no ATP can be synthesised, so no subsequent oxidative phosphorylation

Question 15

What is non-shivering thermogenesis ?

Answer 15

Brown adipose tissue contains uncoupling protein (UCP)
-UCP creates a proton leak across the inner mitochondrial membrane
-UCP generates heat by short-circuiting the mitochondrial battery
-Energy from H+ gradient used to generate heat instead of ATP
-UCP requires free fatty acids for activation; cold -> noradrenaline -> lipolysis

UCP is a thermogenin

Brown adipose cells have more mitochondria than white

Question 16

What has more brown fat

Answer 16

We have barely any babies have more

Question 17

What is P/O ratio ?

Answer 17

Number of molecules of inorganic phosphate (Pi) incorporated into ATP per atom of oxygen used
-A measurement of the coupling of ATP synthesis to electron transport
-Depends on the substrate which is oxidised; NADH to NAD+ P/O = 2/5, FADH2 to FAD P/O = 1/5
-Is strongly influenced by Uncoupling Protein Activity

Question 18

How many ATP molecules are prodcued per glucose molecule ?

Answer 18

From 1 molecule of glucose, through glycolysis, the TCA cycle and oxidative phosphorylation, 30-32 ATP molecules are produced