Metabolism 5

Question 1

What are the 5 parts of a mitochondrion?

Answer 1

1. Cristae
2. Intermembrane space
3. Inner membrane
4. Outer membrane
5. Matrix

Question 2

Where is the location of the ETC?

Answer 2

Inner mitochondrial membrane

Question 3

Describe the evolutionary origins of mitochondria.

Answer 3

1. Evolutionary descendant of prokaryote
2. Consumed by a eukaryote - endosymbiotic relationship formed.
3. Rickettsia prowazekii are the nearest living descendants of mitochondria

Question 4

What evidence is there supporting the endosymbiosis theory?

Answer 4

1. Mitochondria can only arise from pre-existing mitochondria/chloroplasts
2. Mitochondria have their own genome - resembles eukaryotes (circular DNA and no histones associated)
3. They have their own protein synthesising machinery
4. They share the same start codon as bacteria - fMet

Question 5

What happens to protons and e- when e- donation occurs by NADH.

Answer 5

Protons go to solvent surrounding enzyme complex

e- go to ETC

Question 6

Write the equation of oxidation of NADH.

Answer 6

NADH + H+ + 1/2O2 ——-> NAD+ + H20

Question 7

Write the equation of oxidation of FADH2.

Answer 7

FADH2 + 1/2O2 ——> FAD + H20

Question 8

What are the 2 steps of oxidative phosphorylation?

Answer 8

1. Protons move from mitochondrial matrix to intermembranal space - controlled by ETC
2. Pumped protons allowed back into Mitochondrial matrix via specific ATP synthase channels

Question 9

What are the 2 gradients that contribute to the proton motive force?

Answer 9

Transmembrane electrical potential gradient and pH gradient

Question 10

What does the ETC consist of?

Answer 10

3 complexes

1. NADH Dehydrogenase complex
2. Cytochrome b-c1 complex
3. Cytochrome Oxidase complex

2 Mobile carriers

1. Co-enzyme Q
2. Cytochrome C

Question 11

Each complex has a higher e- affinity than the last, which allows e- to flow in a logical order.

Answer 11

T

Question 12

What happens every time e- pass through each complex?

Answer 12

Protons are pumped to IMS

Question 13

What does ubiquinone do?

Answer 13

aka co-enzyme Q

transfers e- from NADH Dehydrogenase complex to cytochrome b-c1

Can pick up 1/2 e-

Question 14

Describe cytochrome oxidase.

Answer 14

The last membrane complex in the ETC.

Receives 2e- from cytochrome C, and then it repeats, so cytochrome oxidase receives 4e- in total.

Cytochrome oxidase then passes the e- to oxygen to generate water.

4 H+ also pumped into IMS, which enhances the proton gradient.

4e- + 4H+ + O2 ———> 2H2O

Question 15

Why is O2 an ideal terminal e- acceptor?

Answer 15

It has a high affinity for e-.

Question 16

Negative redox potential means tendency to?

Answer 16

Donate e-

Question 17

Positive redox potential means tendency to?

Answer 17

Accept e-

Each membrane complex has a more positive redox potential than the last so more energetically favourable e- transfer.

As e- pass along the chain, they lose energy

Question 18

Describe ATP synthase.

Answer 18

Consists of:

1. Membrane bound part (F0).
2. Part which projects into matrix (F1)

F0 and F1 have 3 different subunits.

F0 = a, b, c
F1 = alpha, beta, gamma

Question 19

Talk to me about ATP formation using ATP synthase.

Answer 19

1. gamma subunit functions as an assymetrical plate.
2. Beta subunits consequently undergo structural changes.
3. Rotation drives transitions of catalytic portions of Beta subunit, which alters their affinities to ADP and ATP.
4. TORSIONAL energy flows from catalytic subunit to ADP and Pi to promote ATP formation.

This can also work in the other direction to hydrolyse ATP and pump protons out of the matrix. (i.e. dependent on direction of proton flow)

Question 20

FADH2 passes e- directly to ubiquinone (co enzyme Q). What implication does this have?

Answer 20

Fewer protons pumped out so less ATP produced

Question 21

Cyanide and Azide are metabolic poisons. How do they work?

Answer 21

They bind with high affinity to the Fe3+ form of the haem group present in cytochrome oxidase complex.

They therefore inhibit the cytochrome oxidase complex, by blocking the flow of e- through the respiratory chain.

NO ATP produced as a result

Question 22

What does CO do?

Answer 22

Binds to the Fe2+ form of the haem group in cytochrome oxidase, so blocks the flow of e-.

Question 23

Describe malonate.

Answer 23

Malonate very similar to succinate - acts as a competitive inhibitor of succinate dehydrogenase.

Slows down flow of e- from succinate to ubiquinone by inhibiting oxidation of succinate to fumarate.

Question 24

Describe oligomycin?

Answer 24

1. Antibiotic produced by streptomyces - inhibits Oxidative phosphorylation. by binding with ATP synthase stalk.
2. Backlog of protons created, which creates a backlog of e-. H+ conc builds up to saturation point in the IMS.

Question 25

Describe dinitrophenol.

Answer 25

1. Weightloss induced by transporting protons across IMS. This causes uncoupling of oxidative phosphorylation from ATP production and so increases BMR and temperature.

Question 26

What is non-shivering thermogenesis?

Answer 26

UCP-1 (aka thermogenin) is a channel that can be activated to a drop in temp. It allows protons to bypass ATP synthase which releases heat from the dissipation of the proton gradient.