Mitochondria and oxidative phosphorylation

Question 1

Where does oxidative phosphorylation and Krebs cycle take place?

Answer 1

OP: Inner membrane

Krebs Cycle: Matrix

Question 2

What type of genome do mitochondria have?

Answer 2

Circular molecule of DNA

Question 3

What is the origin of mitochondria?

Answer 3

Descendants of a prokaryote.

-Established an endosymbiotic relationship.

Question 4

What are some of the evidence for the endosymbiotic relationship?

Answer 4

Mitochondria can only arise from pre-existing mitochondria (or chloroplasts in the case of plants).
Mitochondria possess their own genome: single stranded.
Mitochondria have their own protein-synthesizing machinery
The first amino acid of mitochondrial transcripts is a formylated methionine residue (fMet) as is the case in bacteria and not methionine (Met) as in eukaryotic proteins.

A number of antibiotics (e.g., streptomycin) that act by blocking bactarial protein synthesis also block protein synthesis within mitochondria.

Question 5

What happens to NADH and FADH2 in the mictochondria?

Answer 5

Within the mitochondria, the co-enzymes NADH and FADH2 are re-oxidised by molecular oxygen in the reactions:
NADH + H+ + 1/2O2—-> NAD+ +H20

FADH2 + 1/2 O2 —-> FADH2 + H2O

Question 6

What is the Delta G for re oxidising NADH and FADH2? WHAT IS THE consequence of this?

Answer 6

NADH: -220
FADH2: -167

Energy released from this is enough to generate lots of phophoanhydride bonds.

Question 7

What does the electron transport chain consist of?

Answer 7

3 complexes and 2 electron carriers:
Enzymes:

NADH Dehydrogenase complex
Cytochrome b-c1 complex
Cytochrome oxidase complex

Carriers:
Ubiquinone (a.k.a. co-enzyme Q)
Cytochrome C.

Question 8

What happens in the ETC?

Answer 8

-when electrons pass through each complex, protons are pumped to the intermembrane space.
-Ubiquinone picks up 1 or 2, together with an H+ from solution.
- Cytochromase oxidase is the last membrane complex. It initially receives 2 electrons from cytochrome c. Then cycle repeats to get 4 electrons in total.
so 4 protons are pumped, increasing pH gradient.

Question 9

What happens to the electrons picked up by the complexes?

Answer 9

Passed onto oxygen to generate water.

Question 10

Why is oxygen a good terminal acceptor?

Answer 10

High affinity for electrons

Question 11

positive E’0 implies:

negative E’0:

Answer 11

positive E’0 implies that the redox couple has a tendency to accept electrons and therefore has more oxidising power than hydrogen.

Question 12

Explain the structure of ATP synthase?

Answer 12

ATP synthase is a multimeric enzyme consisting of a membrane bound part (F0) and a F1 part which projects into the matrix space.
F0: a,b, and c
F1: alpha, beta and gamma
Rotation of the enzyme drives transitions states, with altering affinities for ATP and ADP.

Question 13

How does succinate dehydrogenase affect ATP production?

Answer 13

It is firmly attached to the inner surface of the mitochondria, has direct communication with ubiquinone. The FADH2 produced by this reaction using this enzyme, directly passes electrons to ubiquinone and therefore less ATP produced as protons are not pumped.

Question 14

Explain the mechanisms of action of metabolic poisons?

Answer 14

Cyanide:
Cyanide and Azide bind with high affinity to the ferric (Fe3+) in the cytochrome oxidase complex, blocking flow of electrons and stops ATP production.

Carbon monoxide binds to ferrous form of the haem group, also blocking flow of electrons.

Malonate:
acts as a competitive inhibitor of succinate dehydrogenase. Slows down the flow of electrons from succinate to ubiqonine by inhibiting the oxidation of succinate to fumerate.

Oligomycin:

• Antibiotic produced by streptomyces. Binds within the stalk of ATP synthase
• ATP synthase is blocked, so build up of protons in the intermembrane space.
• therefore no more protons pumped as conc too high even for AT

Dinitrophenol:

• induces weight loss
• uncouples oxidative phosphorylation from ATP production- provides alternative pathway for protons to travel through the membrane
• increases metabolic rate and body temperature

Question 15

what is non-shivering thermogenesis?

Answer 15

• uncoupling of oxidative phosphorylation.
• UCP-1: thermogenin is a channel that can be activated in response to drop in core body temp
• allows protons to bypass ATP synthase, thereby releasing heat from proton gradient.

Question 16

Succinate dehydrogenase is attached to the inner surface of the inner mitochondrial membrane and passes electrons directly to which molecule?

Answer 16

FAD

Question 17

Mitochondrial respiration can be readily measured using what?

Answer 17

An oxygen electrode.

Question 18

The diagram shows the multimeric enzyme structure known as ATP synthase, consisting of a membrane bound domain (F0) and an F1 domain projecting into the mitochondrial matrix space. Protons passing back into the matrix via a pore in the F0 domain drive movement of the F1 domain, with the resulting torsional energy driving ATP production via the F1 domain.

Answer 18

Correct! The F0 portion is membrane bound and contains a pore through which the protons pass back into the matix. Passage of protons through this pore results in movement of the F1 domain. The F1 domain contains the distinct “lollipop” head composed of alpha, beta and gamma subunits which catalyses either the formation or hydrolysis of ATP depending upon the direction of flow of protons (to or from the matrix).