Energy Production In Carbohydrates 4

Question 1

Where does the pyruvate reaction take place?

Answer 1

Mitochondrial matrix

Question 2

What reaction takes place in pyruvate reaction?

Answer 2

Pyruvate + CoA + NAD+ -> acetyl CoA + CO2 + NADH + H+

Question 3

What enzyme is used in pyruvate reaction?

Answer 3

Pyruvate dehydrogenase

Question 4

What provides the cofactors for PDH?

Answer 4

B vitamins, therefore reaction is sensitive to vitamin B1 deficiency

Question 5

Is the pyruvate reaction reversible?

Answer 5

Reaction is irreversible

Question 6

What can inhibit the pyruvate reaction?

Answer 6

Acetyl CoA
NADH
ATP
Citrate

Question 7

What can activate the pyruvate reaction?

Answer 7

CoASH
NAD+
ADP
Insulin

Question 8

What can a PDH deficiency result in?

Answer 8

Lactic acidosis

Question 9

Where does the Krebs cycle take place?

Answer 9

Mitochondria

Question 10

What happens in the Krebs cycle?

Answer 10

Acetyl is converted to 2CO2
Oxidative as requires NAD+ and FAD
Some energy is produced as ATP/GTP

Question 11

What is produced in the Krebs cycle for every glucose molecule?

Answer 11

Krebs cycle occurs twice for each glucose molecule
6 NADH
2 FADH2
2 GTP

Question 12

How is the Krebs cycle regulated in general?

Answer 12

Regulated by energy availability (ATP/ADP ratio, NADH/NAD+ ratio)

Question 13

How is the Krebs cycle regulated at isocitrate to C5?

Answer 13

Isocitrate dehydrogenase enzyme used

Stimulated by ADP, inhibited by NADH and ATP

Question 14

How is the Krebs cycle regulated at alpha-ketoglutarate (C5) to succinyl-CoA (C4)?

Answer 14

Alpha-ketoglutarate dehydrogenase enzyme used

Inhibited by NADH, ATP and succinyl-CoA

Question 15

What is the Krebs cycle a central pathway for?

Answer 15

Catabolism of sugars, fatty acids, ketone bodies, amino acids and alcohol

Question 16

Can the Krebs cycle occur in the absence of O2?

Answer 16

No, cannot function

Question 17

Electron transport

Answer 17

Inner mitochondrial membrane highly impermeable
Electrons transferred through series of carrier molecules to O2, with release of energy
Some energy lost as heat
H+ gradient across inner mitochondrial membrane = proton motive force

Question 18

What is the equation for proton translocating ATPase (ATP synthase)?

Answer 18

ATP + 2H+ ADP + Pi + 2H+
LHS is in mitochondrial matrix, RHS is in cytoplasm
2 H+ travel from mitochondrial matrix across inner membrane to intermembrane space

Question 19

What happens in ATP synthesis?

Answer 19

Return of H+ is favoured energetically by electrochemical gradient
H+ can only return across membrane via ATP synthase which drives ATP synthesis

Question 20

What is oxidative phosphorylation?

Answer 20

Electron transport coupled to ATP synthesis
Electrons are transferred from NADH and FADH2 to molecular oxygen
Energy released used to generate proton gradient
Energy from dissipation of proton motive force is coupled to synthesis of ATP from ADP

Question 21

How is oxidative phosphorylation regulated?

Answer 21

Regulated by mitochondrial [ATP]
When [ATP] high, [ADP] low, no substrate for ATP synthase
Therefore inward flow of H+ stops
Conc of H+ in intermitochondrial space increases
Prevents further H+ pumping, stops electron transport
Reverses with low [ATP]

Question 22

Inhibition of oxidative phosphorylation

Answer 22

Inhibitors block electron transport

E.g. cyanide prevents acceptance of electrons by O2 as it binds more tightly than O2

Question 23

Uncoupling of oxidative phosphorylation

Answer 23

Uncoupled increase permeability of mitochondrial inner membrane to protons
Dissipate proton gradient, reduces proton motive force
No drive for ATP synthesis

Question 24

Efficiency of coupling of oxidative phosphorylation

Answer 24

Rest of energy lost as heat
Efficiency depends on tightness of coupling
Can be varied in some tissues

Question 25

Brown adipose tissue

Answer 25

Allows extra heat generation
Contains thermogenin (UCP1)
In response to cold, noradrenaline activates many processes including lipase to release fatty acids from triacylglycerol
Electron transport uncoupled from ATP synthesis, energy is released as extra heat
Found in newborn infants