Carbohydrate & Krebs & ETC

Question 1

Explain the role of pyruvate dehydrogenase in glucose metabolism

Answer 1

Pyruvate transported across mitochondrial membrane then enzyme converts pyruvate to acetyl CoA – IRREVERSIBLE = key regulatory step – requires cofactors, can be allosterically regulated (high energy = off)

Question 2

What happens when there is PDH deficiency?

Answer 2

Won’t pass pyruvate to the TCA = build up, need to replenish NAD+ = LDH activity increases = pyruvate to lactate = lactate acidosis

Question 3

Briefly what is the TCA cycle?

Answer 3

Introducing a acetyl-CoA 2C + 4C = citrate 6C

recover reducing equivalents NADH FADH2,
prod GTP by substrate level phosphorylation,
release C from acetyl CoA as CO2,
Isomerisation,
Oxidative steps
Prod precursors for biosynthesis
NEEDS O2

Question 4

How many TCA cycles from every glucose entering glycolysis?

Answer 4

2

Question 5

What does TCA stand for?

Answer 5

Tricarboxylic acid cycle

Question 6

What is the role of the TCA cycle in metabolism?

Answer 6

Removal of reducing power

Question 7

Explain how the TCA cycle is regulated

Answer 7

enzymes catalysing reactions are allosterically regulated, isocitrate oxidised to alpha-ketoglutarate = irreversible = key regulatory step that removes reducing power, where CO2 is reduced = irreversible

Question 8

What is oxidative phosphorylation?

Answer 8

oxidative phosphorylation is when ATP is generated from the oxidation of NADH/FADH2 and subsequent transfer of electrons and pumping of protons e.g. ETC

Question 9

The TCA cycle supplies the biosynthesis of what?

Answer 9

Fatty acids, AA, Haem, glucose

Question 10

Why will the TCA cycle not function in the absence of O2?

Answer 10

Prod a lot of NADH and FADH if no oxidation this pathway will stop

Question 11

With regards to permeability what is the structure of the mitochondria?

Answer 11

Porous outer membrane, then intermembrane space, inner impermeable membrane contains the matrix

Question 12

What is the role of oxidative phosphorylation in energy production?

Answer 12

To generate ATP from the oxidation of NADH/FADH2

Question 13

Explain the process of the ETC

Answer 13

NADH passes the captured electrons to a ‘proton translocating complex’ in the inner mitochondrial membrane, as this occurs the electrons give up a little bit of energy to pass 2H+ through the inner mitochondrial membrane to the intermembrane space – the electrons are then passed to PTC2 with removal of 2H+ and then PTC3 with removal of 2H+ - finally the electrons are picked up by O + 2H+ to form H2O = creating a H+ gradient

Question 14

What is the H+ gradient in the mitochondria also known as?

Answer 14

Proton motive force (pmf)

Question 15

How is ATP produced in the ETC?

Answer 15

ATP synthase = uses the pmf – takes 2H+ back into the matrix which subsequently = ADP + P ATP

Question 16

How can oxidative phosphorylation be inhibited?

Answer 16

Cyanide binds haem very strongly = prevents acceptance of e- by O2 in the final ETC – reducing the creation of pmf.

Stops transport of e- and ATP prod

Question 17

Describe how, when and why uncoupling of oxidative phosphorylation occurs in some tissues

Answer 17

Whole process is dependent on the permeability of mitochondria – increase permeability = dissipates the pmf and stops ATP prod e.g. dinitrophenol, fatty acids

Uncoupling can occur in brown adipose tissue – stops electron transport but produces heat (babies, hibernating animals)

Question 18

What is substrate level phosphorylation?

Answer 18

Substrate level phosphorylation is directly phosphorylating ADP with a phosphate and energy is provided from a coupled reaction e.g. in the krebs cycle and glycolysis

Question 19

Compare substrate level phosphorylation and oxidative phosphorylation

Answer 19

Substrate level phosphorylation
directly phosphorylating ADP with a phosphate and energy is provided from a coupled reaction – can occur in absence of O2,

oxidative phosphorylation
ATP is generated from the oxidation of NADH/FADH2 and subsequent transfer of electrons and pumping of protons – cannot occur in absence of O2

Question 20

Overall what is the net production of ATP?

Answer 20

32

Question 21

A lot of energy is lost in ATP production as?

Answer 21

heat