M2b L14-15

Question 1

Outline the structure and function of the ATP synthase complex

Answer 1

protein a has a tunnel that protons go through to get to the c ring, take one turn and exit the other side of protein a, rotating shaft forces conformational changes onto F1, this is how ATP is made

Question 2

Describe the binding change model of ATP synthesis

Answer 2

The F1 unit consists of 3 ɑβ-subunits. One ɑβ-subunit forms one catalytic side. It exists in 3 conformations:
O open
L loose
T tight
The rotation of the mechanically forces the catalytic side to adopt 3 conformations, they are always in the same sequence O → L → T → etc

Question 3

Explain why more ATP can be produced from NAD-linked substrates compared with FAD linked substrates

Answer 3

NADH passes its electrons to Complex I, production of ~2.5 mol ATP by oxidative phosphorylation
FADH2 passes its electrons directly to UQ, production of ~1.5 mol ATP by oxidative phosphorylation
it skips Complex I so it makes less mols of ATP

Question 4

Explain why the rate of flux through the ETC is closely linked to the need for ATP and the rate of flux through the TCA cycle

Answer 4

The rate of ATP utilization regulates the rate of ATP synthesis
In cells using ATP, it causes ADP to accumulate
This stimulates ATP synthase and TCA cycle
ATP production → proton gradient decreases → electron transport increases → oxidation of NADH to NAD+
Increased levels of NAD+ → stimulates TCA cycle

Question 5

Identify sites of action of some inhibitors of the electron transport chain

Answer 5

ATP synthase can be inhibited by oligomycin, blocks ATP synthesis, Builds up of protons in intermembrane space blocks electron transport

Question 6

Distinguish between inhibition of the electron transport chain and uncouplers of ATP synthesis

Answer 6

Inhibitors block oxidation and reduce both ATP generation and oxygen consumption
uncouplers disrupt the mitochondrial membrane and reduce ATP production but increase oxygen consumption.

Question 7

Explain why uncoupling protein one can lead to thermogenesis

Answer 7

acids and bases together heat up, it releases energy as heat

Question 8

Outline the two shuttle systems for transport of reducing equivalents across the mitochondrial inner membrane and explain their metabolic importance

Answer 8

Malate-aspartate shuttle releases NADH into the mitochondrial matrix
OAA and NADH/H+ is converted to malate and NAD+, once in the cytosol, it is converted back to OAA by reverse reaction
Glycerol-phosphate shuttle yields FADH2 instead of NADH

Question 9

Explain why ATP yield from the complete oxidation of glucose depends on which shuttle system is used

Answer 9

NADH produces more ATP mol than FADH because FADH skips Complex I

Question 10

exam question

explain the biochemistry of thermogenesis in the newborn and in hibernating animals that can be attributed to uncoupling protein-1

Answer 10

Uncoupling protein-1 is regulated by transcription, it is produced as a result of signaling systems activated by the hypothalamus to stimulate lipolysis in brown adipose tissue. it transports H+ from the intermembrane space back into the matrix of the mitochondrion. The change in free energy that accompanies this passage is released as heat

Question 11

Where is O2 used and why is it necessary? What is formed directly from the O2 molecules?

Answer 11

Oxygen is the final electron acceptor in the electron transport chain. It becomes reduced,
forming water. Oxygen is needed because it is at a lower electron potential than any other
compound in the chain