2. TCA cycle

Question 1

What enzyme converts pyruvate to Acetyl CoA?

Answer 1

Pyruvate dydrogenase

Question 2

Which vitamin deficiency affects PDH?

Answer 2

Vitamin B1 - cofactors

Question 3

What molecules activate PDH?

Answer 3

Pyruvate
NAD+
ADP
Insulin
 = low energy signals

Question 4

How is PDH activated?

Answer 4

Dephosophorylated

Question 5

How is PDH inactivated?

Answer 5

Phosphorylated

Question 6

What molecules inhibit PDH activity?

Answer 6

Citrate
ATP
NADH
Acetyl CoA

Question 7

What will happen if there is PDH deficiency?

Answer 7

Pyruvate built up, NAD+ restored by conversion to lactate…lactic acidosis

Question 8

Where does the TCA cycle happen?

Answer 8

Mitochondria

Question 9

What are the 2 key rate-limiting enzymes in the TCA cycle?

Answer 9

isocitrate dehydrogenase

alpha-ketoglutarate dehydrogenase

Question 10

What is the net production of NADH, GTP and FADH2 from one glucose in the TCA cycle?

Answer 10

6 NADH
2 FADH2
2 GTP
(2 Acetyl CoA per glucose)

Question 11

Does the TCA cycle happen in absence of O2?

Answer 11

No, as no NAD+ and FAD

Question 12

By what process are ATP and GTP synthesised in glycolysis and TCA cycle?

Answer 12

substrate- level phosphorylation

Question 13

Where does the electron transport chain happen?

Answer 13

Inner mitochondrial membrane

Question 14

What 2 processes are there in stage 4 of carbohydrate metabolism?

Answer 14

1. Electron transport chain

2. Oxidative phosphorylation

Question 15

How many protein translocating complexes are there in the ETC?

Answer 15

3

Question 16

Which PTC do NADH and FADH2 feed into?

Answer 16

NADH -1

FADH2 -2 as it has less energy so only pumps 4H+ across

Question 17

What is the final electron acceptor?

Answer 17

O2 - becomes H20

Question 18

What is the function of pumping hydrogen ions into the inter membrane space?

Answer 18

Hydrogen gradient is established - proton motive force which is used to synthesise ATP

Question 19

How is ATP synthase regulated?

Answer 19

When [ATP] is high, there is no ADP substrate.
Inward flow of H+ stops and [H+] in intermembrane space increases, preventing electron transport.
Reverses with ADP available.

Question 20

How does cyanide affect electron transport?

Answer 20

Inhibitor of complex IV (cytochrome c).
Prevents acceptance of electrons by O2, the electon transport chain stops and the proton motive force driving ATP synthesis fails

Question 21

What do uncouplers do?

Answer 21

Increase the permeability of the mitochondrial inner membrane to protons.
Protons bypass ATP synthase. Thus, instead of being converted to ATP, the energy from the electron transport chain is released as heat.

Question 22

What are examples of uncouplers?

Answer 22

Fatty acids

Dinitrophenol

Question 23

Efficiency of oxidative phosphorylation depends on what?

Answer 23

Tightness of coupling (impermeability of IMM)

Question 24

How does brown adipose tissue carry out thermogenesis?

Answer 24

In response to cold, NA activates lipase which releases FA from TAG.
FA are oxidised to produce NADH and FADH2 which enter ETC.
FA activates UCP1 to uncouple ETC.
Energy of pmf is released as heat.

Question 25

What is UCP1?

Answer 25

Naturally occurring thermogenin uncoupling protein in brown adipose tissue.
Role in heat generation.

Question 26

What age group have the most brown adipose tissue present?

Answer 26

Newborn infants

Question 27

How do inhibitors and uncouplers differ?

Answer 27

With uncouplers electron transport continues but with heat production rather than ATP production whereas with inhibitors both the transport of electrons and ATP production stop.

Question 28

What is the anabolic role of the TCA cycle?

Answer 28

Provide intermediates for the synthesis of various important molecules such as haem, fatty acids, glutamate and aspartate

Question 29

How are superoxide radicals produced by mitochondria?

Answer 29

During oxidative phosphorylation about 0.1 - 2% of electrons do not reach the end of the electron transport chain and they prematurely reduce oxygen to from superoxide radicals (O2-).

Question 30

What processes does the TCA cycle provide precursors for?

Answer 30

• Amino acid synthesis
• Haem synthesis
• Fatty acid synthesis
• Glucose synthesis