Acetyl CoA And Citric Cycle

Question 1

Where is pyruvate transferred to in aerobic respiration and why

Answer 1

Mitochondria to be converted into acetyl coA

Question 2

Which enzyme removed/ oxidises pyruvate of H+

Answer 2

Pyruvate dehydrogenase

Question 3

What is pyruvate dehydrogenase part of

Answer 3

A multi enzyme complex with other enzymes involved

Question 4

Apart from dehydrogenase removing oxidating pyruvate what happens

Answer 4

Decarboxylation

Question 5

Which vitamins are needed to convert pyruvate to acetyl coa

Answer 5

B1- thiamine pyrophosphate

Riboflavin- FAD

Niacin- NAD

Question 6

Explain the process of reducing pyruvate using the 3 cofactor vitamins aswell as pyruvate dehydrogenase

Answer 6

Thiamine pyrophosphate removes H from pyruvate to produce thiamine

This then passes it to FAD to be reduced into FADH2

This then allows reduction by passing of H to nad to produce NADH2

Question 7

Apart from the pyruvate conversion to acetyl coa , what other fates does it have

Answer 7

1- pyruvate can be turned into fatty acids to then be stored as triglycerides storage for energy

2- can be turned into amino acids for anabolic growth

3- anaerobic respiration into lactate

Question 8

How is pyruvate converted to amino acids

Answer 8

Addition of amine groups

Question 9

How is pyruvate converted into lactate to regenerate NAD in anaerobic respiration

Answer 9

NADH is oxidised and 2H is used to reduce pyruvate producing lactate

Question 10

What happens when lactate is produced , how can it be converted back if 02 is present

Answer 10

Lactate dehydrogenase removed H and converts it back into pyruvate

Question 11

What occurs in yeast when pyruvate is reduced by NADH into NAD?

Answer 11

It produces ethanol

Question 12

What is the net gain from pyruvate dehydrogenase process (2 cycles)

Answer 12

2 x acetyl coa

2 co2

2 NADH

Question 13

What is the main importance of the citric acid cycle/ Krebs cycle

Answer 13

Forms reducing power (NADH and FADH)

Question 14

What type of reaction occurs that joins oxaloacetate (4C) with acetyl coA (2C)

Answer 14

Condensation reaction

Question 15

Which enzyme catalyses the condensation of oxaloacetate with acetyl coA into citrate

Answer 15

Citrate synthase (6C)

Question 16

What happens to citrate 6C when produced by condensation citrate synthase

Answer 16

Rearrangement occurs

Citrate into isocitrate (isomer of citrate)

Question 17

How is citrate rearranged into isocitrate (which enzyme)

Answer 17

Aconitase enzyme

Question 18

What happens to isocitrate to be converted into a- ketoglutarate

Answer 18

Gets oxidised by isocitrate dehydrogenase which converts NAD into NADH

Also gets decarboxylated

Question 19

What is it called when eg isocitrate gets both dehydroxylated by isocitrate dehydrogenase and decarboxylated removing co2

Answer 19

Oxidative decarboxylation (occurs to pyruvate aswell)

Question 20

What happens to a-ketoglutarate (5C) when produced from isocitrate dehydrogenase

Answer 20

Oxidative decarboxylation again (forming NADH and co2)

This forms succinyl coA (thioester bond)

Question 21

Which enzyme oxidative decarboxylates a keto glutarate

Answer 21

A ketoglutarate dehydrogenase

Question 22

How is succinyl coA formed (4C)

Answer 22

CoA is added to form thioester with a ketoglutarate produced by isocitrate dehydrogenase

CoA -S- forms a thioester with a ketoglutarate

Question 23

What happens when the thioester bond on succinyl coA is hydrolysed

Answer 23

Used to generate GTP from GDP + pi

Energy production

Question 24

What happens when the succinyl coA thioester is hydrolysed

Answer 24

Succinyl coA synthetase regenerates a succinate molecule (4C)

Question 25

How is succinate converted into fumarate (4C)

Answer 25

Succinate dehydrogenase reduces FAD into FADH oxidising succinate into fumarate

Question 26

What happens when fumarate is produced

Answer 26

Converted into malate by fumarase enzyme

Adds H2O molecule (hydration)

Question 27

Where in the Krebs cycle does hydration h20 happen

Answer 27

Fumarate into malate

Question 28

How is malate converted into oxaloacetate

Answer 28

Malate dehydrogenase reduces NAD into NADH

Question 29

What is the net gain of Molecules in 2 Krebs cycles

Answer 29

6 NADH

2 FADH

4 co2

2 GTP

Question 30

Why is citric cycle called amphibollic

Answer 30

Both used for anabolic purposes and catabolic

Question 31

What is oxaloacetate used to generate in anabolic reactions

Answer 31

Aspartate which can produce amino acids or purines like atp

Question 32

What can citrate be used to generate

Answer 32

Fatty acids for storage etc

Question 33

What can a ketoglutarate be used to produce

Answer 33

Glutamate into amino acids

Question 34

What is succinyl coa importent for

Answer 34

Porphyrin and heme in RBCs

Question 35

Which 3 enzymes in citric acid cycle are controlled

Answer 35

Pyruvate dehydrogenase

Isocitrate dehydrogenase

A ketoglutarate dehydrogenase

Question 36

When is pyruvate dehydrogenase activated and inactivated

Answer 36

Active when- ADP present, a lot of pyruvate

Inactive when - a lot of acetyl coa or atp or NADH present

Question 37

When is isocitrate dehydrogenase activated and inactive

Answer 37

Activated when - a lot of ADP which needs to be produced into ATP

Inactive when - too much ATP or NADH present

Question 38

When is a ketoglutarate dehydrogenase active and inactive

Answer 38

Active when - ADP present (low energy),

Inactive when - too much coa , succinyl , atp or dehydrogenase

Question 39

How is acetyl coA turned into fat storage for energy

Answer 39

Converted to fatty acids then into triglycerides with the help of citrate

Question 40

Why can triglycerides be used for energy storage

Answer 40

Because when broken down (oxidised) the fatty acids can be converted back into acetyl coA for the citric acid cycle