T2 L3 Mitochondrial respiratory chain

Question 1

Describe the mitochondrial membrane structure

Answer 1

Outer membrane - freely permeable to small molecules & ions
Inner membrane - impermeable to small molecules & ions, including H+. ETC is located here

Question 2

Describe complex I

Answer 2

NADH dehydrogenase
Catalyses 2 simultaneous & coupled processes
1) Electrons are passed to FMN to produce FMNH2
2) Electrons then transferred to a series of iron-sulphur clusters
3) Electrons then transferred to coenzyme Q or ubiquinone

Pumps 4 protons from the matrix into the intramitochondrial membrane (endergonic transfer)
NAD+ goes back to the citric acid cycle to pick up electrons & be reduced

Question 3

What is the reaction at complex I?

Answer 3

NADH + H+ + Q = NAD+ + QH2

Question 4

Describe complex II

Answer 4

Succinate dehydrogenase
Only complex which doesn’t pump protons
1) Electrons of FADH2 pass to complex II
2) Electrons pass from complex II to ubiquinone

Question 5

Describe complex III

Answer 5

Ubiquinone cytochrome C oxidoreductase

Question 6

Describe complex IV

Answer 6

Cytochrome oxidase
Proton pump
Carries electrons from cytochrome C to molecular oxygen
Produces water

Question 7

What do the 3 specific systems in the mitochondrial membrane do?

Answer 7

Transport ADP & Pi into the matrix
Synthesis ATP
Transport ATP into the cytosol

Question 8

What are the 3 systems in the inner mitochondrial membrane?

Answer 8

Adenine nucleotide translocase
Phosphate translocase
ATP synthase

Question 9

Describe adenine nucleotide translocase

Answer 9

Integral protein of inner mitochondrial membrane
Transports ADP3- from intramitochondrial membrane space into the matrix
ADP3- is exchanged for an ATP4- molecule

Question 10

What is an anti porter?

Answer 10

Brings one thing in and one thing out

Question 11

What is atractyloside

Answer 11

Glycoside isolated from a thistle

Specific inhibitor of adenine nucleotide translocase

Question 12

Describe phosphate translocase

Answer 12

Essential for oxidative phosphorylation & synthesis of ATP
Transports phosphate & hydrogen ions into the matrix
Favoured by transmembrane proton gradient

Question 13

What is a symporter?

Answer 13

Brings two things in or two things out

Question 14

Describe ATP synthase

Answer 14

F-type ATPase
2 functional domains
Beta subunits are arranged alternately with alpha subunits. Form a knob-like structure that is held by a stalk of the gamma & E (symbol). Delta subunits interacts with 2 b subunits of F0.

Question 15

What are the 2 functional domains of ATP synthase?

Answer 15

F0 - oligomycin sensitive proton channel. Comprised of 3 different subunits: a,b&c. Forms a complex of 13-15 subunits. Subunits c1-10 are arranged in a circle.
F1 - ATP synthase. Comprised of 5 different subunits: alpha 3, beta 3, gamma, delta & E (symbol)

Question 16

Describe the theory of rotational catalysis

Answer 16

3 beta subunits take it in turns to catalyse synthesis of ATP
Any given beta subunit starts in a conformation for binding ADP & Pi
Then changes conformation so the active site now binds the ATP product tightly
Then changes conformation to give the active site a very low affinity for ATP so ATP is released

Question 17

How much ATP is yielded from 1 molecule of glucose

Answer 17

30 or 32

Question 18

How do uncouplers dissipate the pH gradient?

Answer 18

They transport H+ back into the matrix of the mitochondria & bypass ATP synthase. This severs the link between electron flow & ATP synthesis with the energy being released as heat.

Question 19

Describe uncoupling reagents

Answer 19

It can occur naturally
UCP1 is found in brown adipose tissue & has a specific H+ channel through which the H+ concentration can be dissipated & energy is released as heat
Usually weak acids or bases & are hydrophobic

Question 20

Why are uncoupling reagents hydrophobic?

Answer 20

Allows them to freely diffuse through the inner mitochondrial membrane

Question 21

How is brown adipose tissue adapted for thermogenesis

Answer 21

Specialised for heat generation
High numbers of mitochondria
Mitochondria contain thermogenic (UCP-1)
Important in newborns & may have a role in obesity/diabetes

Question 22

What is DNP?

Answer 22

Exogenous uncoupler
Weak acid
Crosses the membrane by ferrying H+ across
Each DNP molecule collects a proton from inter membrane space & moves through the membrane with it then deposits proton in the matrix.
Can return through the membrane to collect another proton
Toxicity arises from liver damage, respiratory acidosis & hyperthermia