The TCA Cycle and Oxidative Phosphorylation

Question 1

What 3 things go into the Kreb’s cycle?

Answer 1

• glucose (by glycolysis)
• fatty acids (beta oxidation)
• amino acids (transamination)

Question 2

Where does the Kreb’s cycle?

Answer 2

Mitochondrial matrix

Question 3

What tissues does this occur in?

Answer 3

All tissues with mitochondria

Question 4

Give details on the Link’s reaction

Answer 4

Pyruvate is converted to Acetyl CoA
Pyruvate dehydrogenase is needed for this to work
This reaction releases carbon dioxide and NADH
Happens twice as glycolysis produces 2 pyruvate molecules

Question 5

What is the chemical structure of oxaloacetate?

Answer 5

OOC-C=O-CH2-COO

Question 6

What are the 1st 4 reactions of the Krebs cycle?

Answer 6

1) Condensation reaction - oxaloacetate is converted to citrate
2) Isomerisation (citrate to isocitrate)
3) First loss of carbon dioxide
(6 carbon molecule forms a 5 carbon molecule). Isocitrate forms glutarate
4) Second loss of carbon dioxide. Oxoglutarate to succinyl CoA

Question 7

What are the 2nd 4 reactions of the Krebs cycle?

Answer 7

5) Trapping thioester bond energy at GTP (GTP molecule is released here)
6) Conversion of succinate to fumarate (formation of FADH2)
7) Conversion of fumerate to malate
8) Conversion of malate to oxaloacetate

Question 8

What allows the regeneration of glucose from pyruvate?

Answer 8

pyruvate carboxylase

Question 9

What is essential that succinyl CoA makes?

How about glutamate?

Answer 9

Haem

Other amino acids, purines

Question 10

What do you need to add to pyruvate to make oxoloacetate?

Answer 10

COO

Question 11

What are 3 examples of oxidation reactions?

Answer 11

1. Add oxygen directly to a molecule
2. Remove one electron
3. Remove a pair of hydrogen atoms

Question 12

What are some key points on oxidative phosphorylation?

Answer 12

Location - mitochondria (cristae)
Tissues - most tissues except red blood cells
Function - direct phosphorylation of ADP to produce ATP

Question 13

What are the 2 components of the electron transport chain?

Answer 13

1. H pair acceptors (flavin cofactors, coenzyme)

2. Electron acceptors (iron sulphur protein, cytochrome proteins

Question 14

What molecules help transport down the electron chains?

Answer 14

Iron-sulphur proteins - the iron can gain/lose electrons and hence transport them

HAEM ring of cytochrome protein (electron acceptors).

Question 15

What are redox carriers?

Answer 15

• every cofactor involved in oxidation/reduction reaction can be assigned a value known as the oxido-reduction potential
• this redox potential describes the ability of the carrier to donate its electrons to another electron acceptor molecule
• electrons flow from a carrier with a negative E0 to a carrier with a more positive value

Question 16

Explain the movement of electrons in the electron transport chain

Answer 16

The electrons pass down the chain and go down in energy. The energy changes the conformation in the protein which allows them to move the protons from the mitochondrial matrix to the inter-membrane space.

Question 17

What are the two gradients which are created by the movement of protons across the inner membrane?

Answer 17

• pH gradient

- voltage potential

Question 18

What is the change in energy across the membrane to get ADP and Pi to bond?

Answer 18

Kinetic to mechanical

Question 19

What complexes move hydrogen ions out the cell?

Answer 19

1, 3 and 4

Question 20

Give some inhibitors and uncouplers of oxidative phosphorylation

Answer 20

Inhibitors = CN- , CO and rotenone
Uncouplers = DNP, thermogenin protein in brown adipose tissue

Question 21

What does the brown adipose tissue harness the energy from the electron transport chain for?

Answer 21

for heat, not to make ATP

Question 22

When metabolism takes place in aerobic tissue, oxygen utilisation results mainly from:

Answer 22

its reduction to water by cytochrome oxidase

Question 23

How many reactions in the TCA cycle produce NADH and H+ from NAD-?

Answer 23

3

Question 24

The electron transport chain is made up of a chain of electron carriers with:
—– electron affinity and —– redox potential

Answer 24

increasing, increasing

Question 25

If the cells were exposed to an agent which causes the inner mitochondrial membrane to become freely permeable to protons, which of the following effects would you expect to observe?

Answer 25

The ratio of ATP to ADP in the cytosol would fall