Oxidative Phosphorylation

Question 1

What is the location of oxidative phosphorylation in eukaryotes?

Answer 1

Mitochondria, the inner membrane

Question 2

What is the location of oxidative phosphorylation prokaryotes?

Answer 2

The Plasma membrane

Question 3

Describe the structure of mitochondria

Answer 3

• Outer membrane-Permeable to most ions, metabolites etc
• Inner membrane-Contains transporters for metabolites such as pyruvate, citrate, etc. but impermeable to ions
• Intermembrane space-Semipermeable compartment to retain proteins and large ions
• Critae-(Membrane invaginations), provide big surface area
• Matrix- Oxidative metabolism pathways take place here

Question 4

Give an Overview of Oxidative Phosphorylation

Answer 4

• Oxidative Phosphorylation is the last stage of aerobic energy production from all fuels.
• Electrons from TCA cycle reducing equivalents are transferred to oxygen, releasing energy to form ATP.

Question 5

Oxidative phosphorylation Involves 2 distinct but closely coupled processes:

What are the combined reactions?

Answer 5

1. Proton extrusion by the electron transport chain (ETC)
2. ATP synthesis using the proton gradient (ATP Synthase) Combined reactions:

NADH + H+ + ½ O₂ + nADP + nPi → NAD+ + H₂O + nATP

(or FADH₂ + ½ O₂ + nADP + nPi → FAD + H₂O + nATP)

Question 6

Facts and figures about energy requirement

Answer 6

• An average 11 stone adult requires ~2000 kcal energy per day.
• The energy comes mostly from ATP
• 2000 kCal is equivalent to 83 kg ATP
• Actually an 11 stone adult contains 250 g ATP

Question 7

How many of the ~30 molecules of ATP derived from the complete oxidation of a molecule of glucose are generated from oxidative phosphorylation?

Answer 7

26

Question 8

Describe the concept of oxidative phosphorylation

Answer 8

1. Electrons from NADH and FADH2 flow through complexes in the inner mito membrane.
2. This drives export of protons (H+) to the intermembrane space to give a proton gradient
3. This H+ gradient is used by the ATP synthase to make ATP (ADP is phosphorylated).

Question 9

TRUE or FALSE: The use of an ionic gradient to produce energy is called the CHEMIOSMOTIC THEORY

Answer 9

TRUE

Question 10

Draw a diagram of Diagram of Mitchell’s Chemiosmotic Theory

Answer 10

Question 11

Why can’t NADH reduce oxygen directly ?

Answer 11

There is enough energy in this reaction to make 7 ATPs, but such a reaction is unfeasible and uncontrollable.

Question 12

What is the function of the electron transport chain (ETC)?

Answer 12

The ETC allows energy from NADH / FADH₂ to be obtained in small amounts by a series of redox reactions

Question 13

Consider the electron transport chain as a battery

Answer 13

• Electrons are pushed through the electron transport chain (by the reduction potential of the various substrates) and as they pass through the chain, they are used to do work (to pump H+ out through the inner mitochondrial membrane).
• This is just like a battery pushing electrons through a wire, where they are used to do work (for example, to power your mobile phone or a small motor!)

Question 14

Draw a table of the The ETC Enzymes

Answer 14

Question 15

Draw a table of the mobile cofactors

Answer 15

Question 16

Flavin Adenine Nucleotides (FMN, FAD)

Answer 16

These are water soluble or protein bound and carry 2 H on the isoalloxazine ring.

Question 17

Coenzyme Q (CoQ)

Answer 17

This is a lipid soluble carrier of 2 H in the form CoQH2. It diffuses within the membrane.

Question 18

Iron-Sulfur Clusters (Fe-S)

Answer 18

These are e^--carriers and usually accept 1 e^- at a time. They are bound in proteins.

Question 19

Cytochromes

Answer 19

These are small water-soluble haem-containing proteins. They are e^--carriers as the haem-iron can accept single e^-.

Question 20

Electrons pass through the ETC by cycles of redox reactions:

NADH passes e^- to Complex I

Answer 20

Passes electrons to complex I

Green= reduced

Yellow=oxidised

Question 21

Electrons pass through the ETC by cycles of redox reactions:

FADH₂ passes e- to Complex II

Answer 21

Passes electrons to complex II

Question 22

Proton transport by the Electron Transport Chain:

The Classic Loop Model

Answer 22

The ETC wouldn’t work if all cofactors and complexes carried the same electron form.

Question 23

COMPLEX I: NADH-CoQ Reductase

Answer 23

• Huge complex of ~ 34 polypeptides and mass ~ 850 kDa
• Contains FMN, several 2Fe-2S & 4Fe-4S, and CoQ
• It catalyses the overall reaction:
• NADH + H+ + CoQ + 4H+_(matrix) → NAD+ + CoQH₂ + 4H+_(IMS)

4 protons are translocated

Question 24

COMPLEX II: Succinate-CoQ Reductase

(Also contains succinate dehydrogenase)

Answer 24

FADH₂ is bound on Complex II and accepts e- from succinate.

The overall reaction is:

Succinate + CoQ → Fumarate + CoQH₂

There is not enough energy to export H+ to the cytosol

Question 25

COMPLEX III: CoQ-Cytc Reductase

Answer 25

• Accepts electrons from CoQH2 and channels them to Cyt c (via Cyt b and FeS-clusters)
• A “Q-cycle” occurs here and transports 2 extra H+, so in total 4 H+ are pumped from matrix to the intermembrane space
• CoQH₂ + Cyt c_(ox) + 4H+_(matrix) → CoQ + Cyt c_(red) + 4H+ _{(intermem space)}

Complex III is blocked by antimycin A

Question 26

COMPLEX IV: Cytochrome c Oxidase

Answer 26

• Cyto c oxidase collects 4e- from 4 cyt c at its redox centres (Cu and haems) and then passes them to O₂
• 2 H+ are pumped from matrix to intermembrane space per 2 e- (4 per O₂)
• 4 Cyt c_(red) + O₂ + 8H+_(matrix) → 4 Cyt c_(ox) + 2H₂O + 4H+ _(IMS)
• Complex IV is blocked by cyanide

Question 27

Overview of the Electron Transport Chain

Answer 27

Question 28

Alternative overview of the ETC for the reducing agent NADH, showing H/e- acceptors in the complexes

Answer 28