Session 2 Lecture 1

Question 1

What happens to pyruvate after glycolysis?

Answer 1

Does not directly enter the TCA cycle. Has to be oxidised first

Question 2

What enzyme is responsible for the oxidation of pyruvate?

Answer 2

Pyruvate dehydrogenase

Question 3

Where is pyruvate dehydrogenase found?

Answer 3

Mitochondrial matrix

Question 4

Where is the pyruvate oxidised?

Answer 4

Pyruvate transported from the cytoplasm across mitochondrial membrane

Question 5

Describe some features of PDH?

Answer 5

Large multi-enzyme complex (5 enzymes). The different enzymes activities require various cofactors

Question 6

What cofactors do PDH require?

Answer 6

FAD, thiamine pyrophasphate and lipoid acid. B vitamins provides these factors so the reaction is sensitive to vitamin B1 deficiency

Question 7

Why is the oxidation of pyruvate sensitive to vitamin B1 deficiency?

Answer 7

Because B vitamins provide the co-factors needed by PDH

Question 8

Why is the oxidation of pyruvate such a key regulatory step?

Answer 8

Because it is irreversible as carbon dioxide is released

Question 9

What does pyruvate form when oxidised?

Answer 9

Pyruvate oxidised to acetyl coA

Question 10

What inhibits PDH?

Answer 10

Acetyl coA, NADH, ATP and citrate

Question 11

What activated PDH?

Answer 11

Pyruvate, coASH, NAD+, ADP and insulin

Question 12

What does PDH deficiency lead to?

Answer 12

Lactic acidosis

Question 13

Where does the TCA cycle occur?

Answer 13

Mitochondrial matrix

Question 14

Briefly describe what happens during the TCA cycle?

Answer 14

Acetyl coA combines with oxaloacetate to form citrate. This goes on to form isocitrate, then alpha ketoglutarate, then succinyl coA, succinate, fumerate, malate and oxaloacetate

Question 15

Why two steps in the TCA cycle are irreversible and therefore rate limiting?

Answer 15

Isocitrate to alpha ketoglutarate

Alpha ketoglurate to succinyl coA

Question 16

Why are the reactions irreversible?

Answer 16

Because carbon dioxide is produced

Question 17

What enzyme is responsible for the reaction of isocitrate to alpha ketoglurate?

Answer 17

Isocitrate dehydrogenase

Question 18

What enzyme is responsible for the conversion of alpha ketoglutarate to succinyl coA?

Answer 18

alpha ketoglutarate dehydrogenase

Question 19

What biosynthetic pathways do the four carbon products of the TCA cycle stimulate?

Answer 19

Amino acids and haem

Question 20

What is stage four of catabolism?

Answer 20

Electron transport and ATP synthesis

Question 21

What is electron transport?

Answer 21

This is the electrons on NADH and FADH being transferred through a series of carrier molecules to oxygen.

Question 22

What is oxidative phosphorylation?

Answer 22

This is the free energy released being used to drive ATP synthesis

Question 23

What happens in electron transport?

Answer 23

Electrons are transferred through series of carrier molecules to O2 with release of energy. The energy is used by PTCs to move protons to the intermembrane space

Question 24

What is the proton motive force?

Answer 24

This is the gradient of H+ ions formed when they are pumped into the intermembrane space

Question 25

How is the ATP synthesised?

Answer 25

The protons return across the membrane via the ATP synthase hence drive ATP synthesis. The energy disappeared from the pmf is coupled to the synthesis of ATP from ADP

Question 26

How is oxidative phosphorylation stopped?

Answer 26

[ADP] low then no substrate for ATP synthase so inward flow of H+ stops and conc of H+ in intermembrane space increases therefore prevents further H+ pumping and stops electron transport

Question 27

What is the link between oxidative phosphorylation and electron transport?

Answer 27

They are normally tightly coupled

Question 28

What can we say about the ADP levels when ATP is high?

Answer 28

ATP is high then ADP will be low

Question 29

Give some examples of inhibitors of oxidative phosphorylation?

Answer 29

Cyanide and carbon monoxide

Question 30

What do the inhibitors do?

Answer 30

They block electron transport therefore no pmf therefore no oxidative phosphorylation.

Question 31

Give some examples of uncouplers?

Answer 31

Dinitrophenol, dinitrocresol and fatty acids

Question 32

How do uncouplers work?

Answer 32

Increase the permeability of the mitochondrial inner membrane to protons therefore H+ enter mitochondria without driving ATP synthase. Dissipate pmf, no drive for ATP synthesis

Question 33

What happens to energy when you have uncouplers?

Answer 33

The pmf is dissipated as heat

Question 34

What are some natural uncouplers?

Answer 34

Uncoupling proteins (UCP) (there are 5 of them)

Question 35

What is the advantage of these natural uncouplers?

Answer 35

They uncouple the electron transport chain from the ATP production to produce heat

Question 36

Where are the natural uncouplers found?

Answer 36

They are found on the inner mitochondrial membrane

Question 37

Where is UCP1 found?

Answer 37

Previously known as thermogenin. It is expressed in brown adipose tissue and is involved in non-shivering thermogenesis.

Question 38

How does UCP 1 work?

Answer 38

In response to cold, noradrenaline is released from the sympathetic nervous system and stimulates lipolysis releasing fatty acids to provide fuel for oxidation in brown adipose tissue. As a result of -oxidation of the fatty acids NADH and FAD2H are formed, driving ET and increasing the p.m.f. However, noradrenaline also activates UCP1 allowing the protons to re-enter the mitochondrial matrix without driving ATP synthesis, which dissipates the p.m.f as heat rather than ATP.

Question 39

Clinical significance of UCP 2

Answer 39

Could be linked to diabetes, obesity, metabolic syndrome and heart failure

Question 40

Where is UCP 3 found?

Answer 40

Skeletal muscle, brown adipose tissue and the heart

Question 41

Where is brown adipose tissue found?

Answer 41

Newborn infants - to maintain heat around vital organs. Also hibernating animals - to generate heat to maintain body temperature