TCA And Oxidative Phosphorylation

Question 1

What does Pyruvate Dehydrogenase do?

Answer 1

Catalyses the conversion of pyruvate to acetyl CoA, producing CO2 and NADH

Question 2

Where is Pyruvate Dehydrogenase found

Answer 2

Mitochondrial matrix

Question 3

Why is Pyruvate Dehydrogenase sensitivity to a vitamin B1 deficiency

Answer 3

The enzyme activity requires cofactors and B vitamins provide these factors

Question 4

True or false: the reaction catalysed by pyruvate dehydrogenase is reversible

Answer 4

False. It’s irreversible making it a key regulatory step

Question 5

What activates pyruvate dehydrogenase

Answer 5

Pyruvate, CoA, NAD+, ADP and Insulin (low energy signals)

Question 6

What inhibits Pyruvate Dehydrogenase

Answer 6

Acetyl CoA, NADH, ATP, citrate (high energy signals)

Question 7

True or False: Pyruvate cannot be formed from acetyl-CoA

Answer 7

True, the loss of CO2 is irreversible

Question 8

What does a deficiency in pyruvate dehydrogenase lead to

Answer 8

Lactic acidosis (increase in blood lactate levels)

Question 9

Where does the TCA cycle occur

Answer 9

Mitochondrial matrix

Question 10

What does TCA stand for

Answer 10

Tricarboxylic Acid cycle

Question 11

Outline the Kreb’s cycle

Answer 11

• Acetyl CoA binds with the 4 carbon oxaloacetate to form the 6 carbon citrate
• citrate is converted into the 6 carbon isocitrate
• isocitrate dehydrogenase oxidises isocitrate causing the loss of CO2 and production of NADH
• alpha-ketoglutarate is oxidised by alpha-ketoglutarate dehydrogenase causing the loss of CO2 and production of NADH
• compound is modified releasing CoA and producing GTP
• FADH2 is produced
  NADH produced to reform oxaloactetate

Question 12

For 1 molecule of glucose what is produced in the TCA cycle

Answer 12

6 NADH
2 FADH2
2 GTP

Question 13

What are isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase regulated by

Answer 13

High energy signals (ATP and NADH)

Question 14

True of false: alpha-ketoglutarate dehydrogenase is inhibited by its product

Answer 14

True

Question 15

How does the Kreb’s cycle allow for anabolic reactions

Answer 15

It supplies intermediates for biosynthetic processes

Question 16

Give some example of interconversions allowed by the Kreb’s cycle

Answer 16

• citrate to fatty acids
• alpha-ketoglutarate into amino acids
• oxaloacetate into glucose and amino acids

Question 17

Does the Kreb’s cycle occur in the absence of oxygen

Answer 17

No, as the NADH and FADH2 cant offload their hydrogen and so there are no free NAD+ and FAD to pick up hydrogen so the TCA stops

Question 18

By the end of the Kreb’s cycle how much ATP has been produced per glucose

Answer 18

4 ATP

Question 19

Where does oxidative phosphorylation occur

Answer 19

Inner mitochondrial membrane

Question 20

What happens to NADH and FADH2 in oxidative phosphorylation

Answer 20

They are reoxidised

Question 21

Outline the electron transport which occurs before oxidative phosphorylation

Answer 21

NADH and FADH2 offload their electrons through a series of protein translocating complexes. As the electrons are transferred through the chain to oxygen they release energy which move hydrogen across the membrane

Question 22

Energy from what allows the Hydrogen ions to pass into the intermitochondrial space

Answer 22

Energy is released when the electrons are transferred through the protein carrier molecules

Question 23

Why are the electrons transferred through more than one carrier molecule in steps

Answer 23

So that energy is contained and you have more control on the production so less energy is wasted

Question 24

How many hydrogen ions travel through the membrane due to 1 molecule of NADH offloading it’s electron pair

Answer 24

6

Question 25

How many hydrogen ions are transferred through the carrier molecules when 1 molecule of FADH2 offloads it's electron pair

Answer 25

4

Question 26

Why does NADH allow to movement of more hydrogen ions

Answer 26

It's a higher energy molecule

Question 27

What proportion of the energy released by the movement of electrons is used to pump hydrogen ions across the membrane

Answer 27

30% the rest is lost as heat

Question 28

Why is a hydrogen ion gradient allowed to build up

Answer 28

The inner mitochondrial membrane is very impermeable so hydrogen ions can move through easily, they had to move through the carrier molecules

Question 29

What is the proton motive force

Answer 29

The hydrogen ion gradient across the inner mitochondrial membrane

Question 30

What does ATP synthase catalyse

Answer 30

The production of ATP from ADP + Pi as hydrogen ions flow through the enzymes down their electrochemical gradient

Question 31

How many protein translocation complexes do NADH and FADH2 use

Answer 31

NADH -3 | FADH2 -2

Question 32

What happens if the proton motive force is increased

Answer 32

More ATP is synthesised

Question 33

Oxidation of 2 moles of NADH and FADH2 produce how many moles of ATP

Answer 33

NADH- 5 | FADH2 - 3

Question 34

What happens to oxidative phosphorylation if ATP concentration is high

Answer 34

There is a low ADP concentration so there's no substrate for ATP synthase so the inward flow of hydrogen ions stops and the H+ conc in the intermitochondrial space increases stopping the electron transport chain

Question 35

What regulates electron transport and oxidative phophorylation

Answer 35

ATP concentrations

Question 36

What does an inhibitor of oxidative phosphorylation do

Answer 36

Blocks the electron transport by preventing the acceptance of electrons by oxygen

Question 37

Give an example of an oxidative phosphorylation inhibitor

Answer 37

Cyanide and carbon monoxide

Question 38

What are uncouplers

Answer 38

Molecules that increase the permeability of the inner mitochondrial membrane to protons so dissipate the proton gradients reducing the proton motive force so there's no drive for ATP synthesis

Question 39

Give 3 examples of uncouplers

Answer 39

Fatty acids, dinitrophenol and dinitrocresol

Question 40

What are oxidative phosphorylation diseases

Answer 40

Genetic defects in proteins encoded by mtDNA which lead to a decrease in electron transport and ATP synthesis

Question 41

What naturally occurring uncoupling protein does brown adipose tissue contain

Answer 41

Thermogenin

Question 42

How does brown adipose tissue produce extra heat

Answer 42

In response to the cold and noradrenaline lipase releases fatty acids from triacylglycerol and then go on to activate thermogenin (or is oxidised).

Question 43

What does thermogenin do?

Answer 43

Transports H+ back into the mitochondria so the energy from the proton motive force is released as extra heat

Question 44

What mechanism of ATP production is the major process in cells requiring large amounts of energy

Answer 44

Oxidative phosphorylation

Question 45

Which mechanism for ATP production can occur in the absence of oxygen (to some extent)

Answer 45

Substrate level phosphorylation

Question 46

How does energy coupling occur in substrate level phosphorylation

Answer 46

Directly through the formation of high energy from hydrolysis bonds (phosphoryl group transfer)

Question 47

How does energy coupling occur in oxidative phosphorylation

Answer 47

Energy coupling occurs indirectly through generating and using the proton motive force

Question 48

Where does substrate level phosphorylation take place

Answer 48

In the cytoplasm and mitochondrial matrix

Question 49

What is the net yield of ATP from 1 molecule of glucose following the Kreb's cycle (taking into account the NADH and FADH produced)

Answer 49

32