Energy Production - TCA and ETC

Question 1

True or False:

Pyruvate enters directly into Stage 3 (TCA)

Answer 1

False - has to be converted into acetyl coA first

Question 2

Which enzyme converts pyruvate into acetyl coA?

Answer 2

Pyruvate dehydrogenase

Question 3

What is the equation for the conversion of pyruvate into acetyl coA?

Answer 3

CH3COCOOH + CoA + NAD+ –> CH3CO~CoA + CO2 + NADH + H+

Question 4

Where does the conversion of pyruvate to acetyl coA occur?

Answer 4

Mitochondrial Matrix

Question 5

As pyruvate dehydrogenase is a large multi-enzyme complex, how many enzymes does it consist of?

Answer 5

5

Question 6

Why is the conversion of pyruvate to acetyl coA sensitive to Vitamin B1 deficiency?

Answer 6

The different enzyme activities require various cofactors (FAD, thiamine pyrophosphate and lipoid acid) which are provided by B-vitamins

Question 7

Why is the link reaction a key regulatory step?

Answer 7

It is irreversible - rate limiting

Question 8

What does pyruvate dehydrogenase deficiency cause?

Answer 8

Lactic acidosis

Question 9

What is pyruvate dehydrogenase activated by?

Answer 9

Pyruvate, CoA, NAD+, ADP and Insulin

Question 10

What is pyruvate dehydrogenase inhibited by?

Answer 10

Acetyl-CoA, NADH, ATP, citrate

Question 11

Where does the Kreb’s cycle occur?

Answer 11

Mitochondria

Question 12

What are some feature of the Kreb’s cycle?

Answer 12

Single pathway

Acetyl converted to 2CO2

Oxidative (requires NAD+, FAD)

Some energy is produced as ATP and GTP

Produces some precursors for biosynthesis

Question 13

How many cycles of TCA are there per glucose entering glycolysis?

Answer 13

Two

Question 14

What does acetyl coA join with to form citrate (C6)?

Answer 14

Oxaloacetate (C4)

Question 15

How many carbons does isocitrate have?

Answer 15

6

Question 16

What is also produced from the production of a-ketoglutarate (C5) from isocitrate (C6)?

Answer 16

NADH and CO2

Question 17

The C5 molecule a-ketoglutarate combines with CoA to produce succinyl-CoA (C4). What is also produced?

Answer 17

CO2 and NADH

Question 18

What is produced when succinyl-CoA is converted into succinate?

Answer 18

GTP from GDP

Question 19

What is produced when succinate is converted into fumerate?

Answer 19

FADH2

Question 20

How is oxaloacetate produced?

Answer 20

Oxidation of malate (C4) - also converts NAD+ into NADH

Question 21

How many NADH, FADH2 and GTP molecules are produced per glucose from TCA?

Answer 21

6 NADH
2 FADH2
2 GTP

Question 22

How is TCA cycle regulated?

Answer 22

By energy availability i.e. ATP/ADP ratio and NADH/NAD+ ratio

Question 23

Does TCA cycle function in the absence of O2?

Answer 23

No

Question 24

What is stage 4 of catabolism and where does it occur?

Answer 24

Electron transport chain - occurs in mitochondria

Question 25

What happens to NADH and FADH2 in the ETC?

Answer 25

Reoxidised

Question 26

Which type of phosphorylation occurs in the ETC?

Answer 26

Oxidative phosphorylation

Question 27

What happens to electrons in the ETC?

Answer 27

They are transferred through a series of carrier molecules with increasing electronegativity to O2 - the final electron acceptor

Question 28

What is the role of H+ ions in the ETC?

Answer 28

Energy used to move H+ across membrane (a lot of energy released as heat) - H+ gradient established across inner mitochondrial membrane = proton motive force

Question 29

What is the only way in which protons can return across the mitochondrial membrane?

Answer 29

Via ATP synthase - driving ATP synthesis

Question 30

Why does NADH use 3 PTCs while FADH2 only uses 2?

Answer 30

Electrons in NADH have more energy than in FADH2

Question 31

How many moles of ATP are synthesised per oxidation of 2 moles of NADH?

Answer 31

5 moles of ATP

Question 32

How many moles of ATP are synthesised per oxidation of 2 moles of FADH2?

Answer 32

3 moles of ATP

Question 33

How is oxidative phosphorylation regulated?

Answer 33

Eg When [ATP] is high, no substrate for ATP synthase as [ADP] is low Inward flow of H+ therefore stops Concentration of H+ in intermitochondrial space increases This prevents further H+ pumping - stops electron transport

Question 34

What is an example of an inhibitor of electron transport?

Answer 34

Cyanide - prevents acceptance of electrons by oxygen

Question 35

What do uncouplers do?

Answer 35

Increase the permeability of the mitochondrial inner membrane to protons Dissipate the proton gradient, thereby reducing the proton motive force - no drive for ATP synthesis

Question 36

What are some examples of uncouplers?

Answer 36

Dinitrophenol, dinitrocresol, fatty acids

Question 37

What are Ox/Phos diseases?

Answer 37

Genetic defects in proteins encoded by mtDNA - decreases in electron transport and ATP synthesis

Question 38

In brown adipose tissue, what is the degree of coupling controlled by?

Answer 38

Fatty acids (uncouplers) - allows extra heat generation

Question 39

What naturally occurring uncoupling protein does brown adipose tissue contain?

Answer 39

Thermogenesis (UCP1)

Question 40

In brown adipose tissue, in response to cold, what does noradrenaline activate?

Answer 40

1. Lipase which releases fatty acids from triacylglycerol 2. Fatty acid oxidation -> NADH/FADH2 -> electron transport Fatty acids activate UCP1 UCP1 transports H+ back into mitochondria So electron transport uncoupled from ATP synthesis meaning energy of PDF is then released as extra heat

Question 41

What is brown adipose tissue found in?

Answer 41

Newborn infants to maintain heat and hibernating animals to generate heat to maintain body temperature

Question 42

How many moles of ATP are produced per mole of glucose in respiration?

Answer 42

32 moles