6. Energy Production - Carbohydrates (c)

Question 1

What makes a step a key regulatory one?

Answer 1

If it’s irreversible.

Question 2

What activates pyruvate dehydrogenase?

Answer 2

Pyruvate, CoASH, NAD+, ADP, insulin, dephosphorylation.

Question 3

What inhibits pyruvate dehydrogenase?

Answer 3

Acetyl-CoA, NADH, ATP, citrate, phosphorylation.

Question 4

What can a deficiency of pyruvate dehydrogenase lead to?

Answer 4

Lactic acidosis.

Question 5

Where does the Kreb’s cycle take place?

Answer 5

In the mitochondria.

Question 6

Is the TCA cycle oxidative or reductive?

Answer 6

Oxidative, it requires NAD+ and FAD.

Question 7

What three key things come from the TCA cycle?

Answer 7

CO2 (from acetyl CoA), energy (in form of ATP and GTP) and precursors for biosynthesis.

Question 8

How many cycles of the TCA cycle happen per glucose molecule?

Answer 8

2.

Question 9

What is the overall equation for one turn of the Kreb’s cycle?

Answer 9

CH3CO~CoA + 3NAD+ + FAD + GDP + Pi + 2H2O –> 2CO2 + CoA + 3NADH + 3H+ + FADH2 + GTP

Question 10

What regulates the TCA cycle?

Answer 10

Energy availability, the ATP/ADP ratio and NADH/NAD+ ratio.

Question 11

What biosynthetic processes does the TCA cycle provide precursors for?

Answer 11

Amino acid, fatty acid and haemoglobin synthesis.

Question 12

What is driven when NADH and FADH2 are oxidised?

Answer 12

Synthesis of ATP.

Question 13

What two methods use the reducing power to produce ATP?

Answer 13

Electron transport (energy released in steps) and oxidative phosphorylation (free energy drives ATP synthesis).

Question 14

Talk through the key steps in mitochondrial electron transport.

Answer 14

There are three proton trans locating complexes.
PTC1: NADH + H+ (2H+ + 2e-) –> NAD+ + 2e- + 2H+
PTC2: FADH2 (2H+ + 2e-) –> FAD + 2e- + 2H+
PTC3: 2H+ + O + 2e- –> H2O.
In every case, the two electrons produced go to the inner mitochondrial membrane and the two hydrogen ion go to the inter membrane space.

Question 15

What is 30% of the energy released from the electron transport through carrier molecules used for?

Answer 15

To move H+ across the membrane.

Question 16

What is the proton motive force?

Answer 16

The [H+] gradient across the inner mitochondrial membrane.

Question 17

What do the H+ travel through when moving down their electrochemical gradient across the membrane?

Answer 17

ATP synthase.

Question 18

How is the proton motive force generated for oxidative phosphorylation?

Answer 18

When electrons are transferred from NADH and FAD2H to oxygen (the final electron carrier) energy is released. This is used to move hydrogen ions and create the pmf.

Question 19

How many proton translocation complexes do NADH and FADH2 use respectively? Why do they use different numbers?

Answer 19

NADH uses 3 but FADH2 only uses 2 because NADH electrons have more energy than FADH2.

Question 20

How is oxidative phosphorylation regulated?

Answer 20

If ATP is high, then ADP must be low so there is no substrate for ATP synthase. This means the inward flow of H+ stops and the concentration of H+ in the intermitochondrial space increases. Further H+ pumping is prevented and electron transport stops.

Question 21

How is oxidative phosphorylation inhibited?

Answer 21

By inhibitors blocking electron transport so acceptance of electrons by O2 is prevented.

Question 22

What is the effect of uncouplers on oxidative phosphorylation?

Answer 22

Uncouplers increase the permeability of the mitochondrial inner membrane to protons. This dissipates the proton gradient so the pmf is reduced and there is no drive for ATP synthesis.

Question 23

What are the three ways of inhibition oxidative phosphorylation?

Answer 23

Inhibiting electron transport so there is no pmf and no oxidative phosphorylation. Uncouplers that increase permeability of membrane to H+ so there is no pmf or drive to synthesise ATP and no oxidative phosphorylation. Ox/phos disease caused by genetic defects leading to decrease electron transport and ATP synthesis.

Question 24

How does the efficiency of coupling of oxidative phosphorylation vary?

Answer 24

Some of the energy is lost by heat. In brown adipose tissue uncouplers allow for extra heat generation.

Question 25

How do brown adipose tissue release more heat energy?

Answer 25

They have naturally occurring uncoupling proteins, thermogenin. In the cold, noradrenaline activates lipase which releases fatty acids form TAGs. There is fatty acid oxidation, forming NADH and FADH2 and causing electron transport. UCP1 is activated so H+ is transported back into the mitochondria. Extra energy from uncoupled electron transport ATP synthesis is released as extra heat.

Question 26

What two organisms are high brown adipose tissue levels found in?

Answer 26

In newborn infants and hibernating animals.

Question 27

What are four key difference between oxidative phosphorylation and substrate level phosphorylation.

Answer 27

1) OP requires membrane associated complexes but SLP requires soluble enzymes.
2) Energy coupling happens indirectly through generation and utilisation of the pmf in OP but happens directly from formation of high energy hydrolysis bonds in SLP.
3) OP must happen aerobically whereas SLP can happen to a limited extent in anaerobic conditions.
4) OP is a major process of ATP synthesis in cells that require lots of energy, but SLP is only used when OP is unavailable for that cell so doesn’t happen in cells requiring lots of energy.

Question 28

What enzyme catalysed the conversion of pyruvate to acetyl CoA?

Answer 28

Pyruvate dehydrogenase.