TCA cycle- structure and functions of mitochondria

Question 1

Pyruvate to lactate

Answer 1

Uses lactate dehydrogenase

Question 2

Pyruvate to oxaloacetate

Answer 2

Conversion uses pyruvate carboxylase

Question 3

Pyruvate to acetyl-CoA

Answer 3

This is the ‘link reaction’

Pyruvate undergoes oxidative decarboxylation by pyruvate dehydrogenase complex.

This process occurs in the mitochondrial matrix and is irreversible:

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

Question 4

Pyruvate to alanine

Answer 4

This conversion uses pyruvate aminotransferase

Question 5

Transport of pyruvate into mitochondria

Answer 5

Pyruvate enters the mitochondria into the intermembrane space via a porin.

Pyruvate then enters the mitochondrial matrix via a specific protein embedded in the inner mitochondrial membrane.

Question 6

Pyruvate dehydrogenase complex

Answer 6

Contains:
3 enzymes
5 co enzymes

Uses 4 vitamins to create the co enzymes

The complex converts Pyruvate to Acetyl CoA in the mitochondrial.

Question 7

The 5 co-enzymes in the pyruvate dehydrogenase complex

Answer 7

TPP

NAD+

CoA

FAD

Lipoic acid

Question 8

Vitamins essential for the production of the pyruvate dehydrogenase complex

Answer 8

Niacin–> NAD+

Thiamine –> TPP

Riboflavin –> FAD

Pantothenate–> CoA

Question 9

8 intermediates in the TCA cycle- in order

After class i keep some specific facts, more or less

Answer 9

1. Acetyl CoA + oxaloacetate = CITRATE
2. Isocitrate
3. Alpha- ketoglutarate
4. Succinyl CoA
5. Succinate
6. Fumarate
7. L-malate
8. Oxaloacetate

Question 10

Dehydration in the TCA cycle

Answer 10

Occurs when citrate is converted to cis-aconitate

Question 11

Hydration in the TCA cycle [2]

Answer 11

1. Occurs when cis-aconitate is converted into isocitrate.

2. Occurs when Fumarate is converted into L-malate

Question 12

Oxidative decarboxylation in TCA cycle [2]

Answer 12

1. Isocitrate is converted to alpha-ketoglutarate—> release CO2.
2. Alpha ketoglutarate converted to succinyl CoA—> release CO2.

Question 13

SLP in the TCA cycle

Answer 13

Succinyl CoA is converted to succinate to produce GTP, then ATP.

Question 14

Dehydrogenation in the TCA cycle [2]

Answer 14

1. Succinate to fumarate

2. L-malate to oxaloacetate

Question 15

4 methods of regulating the TCA cycle

Answer 15

1. Conversion of pyruvate to Acetyl CoA via pyruvate dehydrogenase complex.
2. Entry of acetyl CoA into the TCA cycle via citrate synthase.
3. Isocitrate dehydrogenase reaction [isocitrate to alpha-ketoglutarate]
4. Alpha-ketoglutarate dehydrogenase [alpha-ketoglutarate to succinyl CoA]

Question 16

Other compounds that feed into the TCA cycle

Answer 16

Fatty acids- undergo beta oxidation and form acetyl CoA= enters TCA cycle.

Amino acids- form acetyl CoA to feed into the TCA cycle.

Question 17

Anaplerotic reaction

Answer 17

Reactions that replenish intermediates in a metabolic pathway.

In the TCA cycle-
Malate and oxaloacetate are replenished.

This keeps the intermediate’s concentrations in a dynamic balance/

Question 18

Glycerol-3-phosphate (G3P) shuttle

Answer 18

Shuttle especially prevalent in the brain and muscle.

The inner mitochondrial membrane is impermeable to NADH.

NADH reduces DHAP to Glycerol-3-phosphate (G3P) via the shuttle.

G3P can enter the intermembrane space where it reduces FAD via the shuttle.

FADH2 carries electrons to ubiquinone in the ETC to produce 1.5 ATP.

Question 19

Malate aspartate shuttle

Answer 19

Predominantly in the liver and heart- shuttle harvest the electrons from NADH.

1. Oxaloacetate in the cytosol is reduced by NADH, to malate.
2. Malate enters the mitochondrial matrix and is oxidised by to oxaloacetate—> reduces NAD+
3. NADH formed transfers electrons to ETC. This produces 2.5 ATP.
4. Oxaloacetate is converted to aspartate. Aspartate is transported to the cytosol using a glutamate exchanger.
5. Cytosolic aspartate is transaminated back into oxaloacetate.

Question 20

Ubiquinone

Answer 20

Coenzyme Q

Lipid soluble benzoquinone with long isoprenoid tail.

The first link between complex II and III in the ETC.

Question 21

Cytochrome c

Answer 21

Small water soluble protein , free to move in the membrane.

Forms a link between complex III and IV in the ETC.

Question 22

NADH dehydrogenase

• Size
• Subunits
• Prosthetic groups

Answer 22

The largest protein complex
in the ETC- Complex I.

42 subunits

FMN and Fe-S prosthetic group.

Question 23

Succinate dehydrogenase

• Size
• Subunits
• Prosthetic groups

Answer 23

The smallest complex the in the ETC- Complex II

Contains 5 subunits

Prosthetic groups: FAD and Fe-S

Question 24

Ubiquinone: cytochrome c oxidoreductase

• Size
• Subunits
• Prosthetic groups

Answer 24

The second largest protein complex in the ETC- Complex III

Contains 11 subunits

Prosthetic groups: Haem, Fe-S

Question 25

Cytochrome Oxidase

• Size
• Subunits
• Prosthetic groups

Answer 25

Second smallest protein complex in the ETC- complex IV.

Contains 13 subunits

Prosthetic groups: Haems and Cu.