Oxidative Phosphorylation

Question 1

What is meant by respiratory control?

Answer 1

Uptake of oxygen by mitochondria is controlled by components of ATP production, Pi and ADP

Question 2

What is the purpose of respiratory control?

Answer 2

To match oxygen uptake to energy requirements

Question 3

Give 5 examples of metabolic poisons

Answer 3

Malonate
Cyanide
Rotenone
Dinitrophenol
Oligomycin
Azide (N3)

Question 4

Mechanism of malonate

Answer 4

Structurally similar to succinate so it is a competitive inhibitor of succinate dehydrogenase. This slows down the flow of electrons from succinate to ubiquinone because it prevents the oxidation of succinate to fumarate.

Question 5

Mechanism of cyanide

Answer 5

Binds with high affinity to the ferric (Fe3+) form of the haem group in the cytochrome oxidase complex. This blocks the flow of electrons through the respiratory chain and consequently the production of ATP halts.

Question 6

What other metabolic poison works in a similar way to cyanide?

Answer 6

Azide

Question 7

Mechanism of Rotenone

Answer 7

An isoflavone found in the roots and seeds of some plants. It blocks the transfer of electrons from complex I to ubiquinone

Question 8

Mechanism of Oligomycin

Answer 8

An antibiotic produced by STreptomyces that blocks oxidative phosphorylation by binding to the stalk of ATP synthase and thereby preventing proton flow.

Question 9

Mechanism of dinitrophenol

Answer 9

A proton ionopore which can shuttle protons across the inner mitochondrial membrane

Question 10

What is oxidative phosphorylation?

Answer 10

The production of ATP using energy derived from the transfer of electrons in an electron transport chain

Question 11

Outline the 2 basic steps of oxidative phosphorylation

Answer 11

1) Translocation of protons from mitochondrial matrix into the intermembrane space (facilitated by the ETC)
2) Pumped protons are allowed back into the mitochondria via a specific channel that is coupled to the enzyme ATP synthase

Question 12

What does the ETC consist of?

Answer 12

2 carriers and 3 enzymes

Question 13

What are these 2 carriers?

Answer 13

Cytochrome C
Coenzyme Q (ubiquinone)- mobile

Question 14

What are the 3 enzymes and where are they situated?

Answer 14

NADH dehydrogenase complex
Cytochrome b-c1 complex
Cytochrome oxidase complex

These are built into the structure of the inner mitochondrial membrane

Question 15

What does NADH do?

Answer 15

It donates a hydride ion which is subsequently split into its constituent components, 2 electrons and a proton

Question 16

What is the order of the electron transport chain?

Answer 16

Electrons donated from NADH to NADH dehydrogenase complex

Coenzyme Q (ubiquinone) next

Then Cytochrome b-c1

Then Cytochrome C

Finally electrons passed onto Cytochrome oxidase which catalyses the final reduction reaction involving oxygen

Question 17

What happens as an electron passes through each protein?

Answer 17

A proton is pumped into the intermembrane space

Question 18

How come the electrons flow in this order?

Answer 18

Flow from a carrier of higher reducing potential to one of lower reducing potential

i. e. low redox potential to high redox potential
i. e. low electron affinity to high electron affinity

Question 19

What makes coenzyme Q mobile?

Answer 19

Long hydrophobic tail which makes it freely soluble and mobile in the non polar interior of the inner mitochondrial membrane

Question 20

Final reduction reaction of cytochorme oxidase

Answer 20

O2 + 4e- + 4H+ -> 2H2O

Question 21

ATP synthase is largely made of two main components which are

Answer 21

F0 = membrane bound component
F1 = projection into matrix

Question 22

Significance of OLT

Answer 22

a series of conformational changes that occur on the beta subunit as the axel of ATP synthase turns

O: site is open and nothing is bound to it
L: Conformational change converts the site into a low affinity state so that ADP and Pi loosely bind to the site.
T:Further conformational change further alters the affinity so that ADP and Pi now become tightly bound. This is now catalytically active and ATP is formed.