The Citric Acid Cycle

Question 1

Where does the citric acid cycle happen

Answer 1

In the mitochondrial matrix

Question 2

How does the citric acid cycle begin

Answer 2

The two carbon acetyl CoA from the bridge reaction reacts with oxaloacetate (4c) from gluconeogensis

Question 3

How much co2 and atp is made in TCA

Answer 3

2 co2

1 atp

Question 4

How much NADH and FADH2 is made in TCA

What does each do

Answer 4

3 NADH

1 FADH2

They carry total 8 electrons by getting reduced

Question 5

What is stage 1 of TCA

Answer 5

Reactions 1-4 where two carbon atoms are oxidized and energy rich electrons are gathered

Question 6

What is stage 2 of TCA

Answer 6

Reactions 5-8 where oxaloacetate is regenerated
one atp is made
energy rich electrons are gathered

Question 7

What enzyme catalyzed stage 1 of TCA

What does it do

Answer 7

Citrate synthase

Condensation reaction where acetyl CoA (4c) and oxaloacetate (2c) are joined together

This makes citryl CoA (6c) intermediate

Question 8

After the 6c citryl CoA intermediate is made what happens

Answer 8

Hydrolysis where the CoA leave and H2O comes in

Makes citrate in the end (6C)

Question 9

In what way does the enzyme citrate synthase interact to make citrate

Answer 9

Is an ordered sequential reaction where oxaloacetate binned to the enzyme and acetyl CoA then the two products leave

It changes it’s confirmation when oxaloacetate binds then when citryl CoA if formed (induced fit)

Question 10

After citrate is made what enzyme catalyzes the second reaction of the TCA

What type of enzyme is it

Answer 10

Acotinase

A Lyase (it removes and form double bonds)

Question 11

What does acotinase do in the second reaction of TCA

Answer 11

Citrate is dehydrated (H and oh removed)

This forms cis-aconitate

Then cis aconitate is hydrated (add h and oh)

This makes isocitrate

Question 12

What is the purpose of the second reaction of TCA

Answer 12

It’s an isomerization reaction where the tertiary oh of citrate is turned into the 2 oh in isocitrate

This part prepares for the next reaction oxidative decarboxylation

Question 13

What is the enzyme that catalyzes the third reaction of TCA

Answer 13

Isocitrate dehydrogenase

Question 14

What does isocitrate dehydrogenase do in the third reaction of TCA

Answer 14

Isocitrate (6 carbons) is oxidized (loses two H) which make NADH and oxalosuccinate (6c)

Oxalosuccinate is decarboxylated (lose co2)

This forms alpha-keto glutarate (a ketone and a carboxylic acid)

Question 15

What catalyzes the 4th reaction of TCA

Answer 15

Alpha keto glutarate dehydrogenase complex

Question 16

What does the Alpha keto glutarate dehydrogenase complex do in the 4th reaction of the TCA

Answer 16

Alpha keto glutarate (5c) is decarboxylated then oxidized

The CoA bind to it via a thioester bond and forms succinyl CoA (4c), co2 and NADH

Like the pyruvate dehydrogenase complex (same enzymes coafotores and e3 is identical)

Question 17

From steps 1 to 4 of the TCA, how many electron are gathered

Answer 17

Nadh was formed two times

Each Nadh takes take electrons to make

4 electrons

Question 18

On stage 2 of TCA what enzyme catalyzed the 5th reaction

Answer 18

Succinyl CoA synthetase

Question 19

What does Succinyl CoA synthetase do in the 5th TCA reaction in stage two

Answer 19

Succinyl CoA does substrate level phosphorylation to turn adp to atp

The thioester bond is cleaved to make the atp, The CoA group on the Succinyl CoA leaves

This forms CoA, atp, and succinate

Question 20

Slide 16

Answer 20

Do we need to. Know diagaram

Question 21

What enzyme catalyzed the 6th reaction in stage two of TCA

Answer 21

Succinate dehydrogenase

Question 22

What does Succinate dehydrogenase do in the 6th reaction of TCA

Answer 22

succinate is oxidized and forms fumarate and FADH2 (not Nadh because not enough energy to do that reaction)

Question 23

What is special about succinate dehydrogenase

Answer 23

Unlike all the other enzymes, succinate dehydrogenase is not is the matrix.

It is part of the electron transport chain in the inner mitochondria membrane

Question 24

What enzyme catalyzes the 7th reaction of TCA and what happens

Answer 24

Fumarase (Lyase)

Fumarate is hydrated (h and oh added)

This forms malate

Question 25

What enzyme catalyzes the 8th reaction of TCA and what happens

Answer 25

Malate dehydrogenase

Malate( 4c) is oxidized to form NADH and regenerates oxaloacetate (4c)

Question 26

What is the delta g of the 8th step of TCA and what does it mean

Answer 26

39.7kj/mol

The reaction is exergonic and happens in the forward direction to reuse oxaloacetate for the next reaction

Question 27

What are the net products of the TCA

Answer 27

2 CO2, 3 NADH, fadh2, ATP, 2H, CoA

Question 28

What two enzymes are regulated in TCA

Answer 28

Isocitrate dehydrogenase

Alpha ketoglutarate dehydrogenase

Question 29

How is Isocitrate dehydrogenase regulated

If inhibited what happens

Answer 29

Is allosterically stimulated by adp

Inhibited by atp and Nadh

If inhibited, there’s more citrate with then goes to inhibit phosphofructokinase from glycoslis

Question 30

How is Alpha ketoglutarate dehydrogenase regulated

Answer 30

Atp inhibits it

It’s products inhibited it (negative feedback)

Question 31

Slide 25

Answer 31

Idk

Question 32

How is oxaloacetate also replenished other then in the TCA

Answer 32

It’s made in gluconeogensis

Pyruvate carboxylase enzyme turns pyruvate to oxaloacetate through adding a co2

This is called an anaplerotic reaction (where is fill up the pathway with oxaloacetate)

Question 33

What does the anaplerotic reaction require

How is it regulates

Answer 33

Acetyl CoA

If the energy charge (atp) is high, glucose is made (no gluconeogensis to make oxaloacetate)

If low TCA is run because gluconeogeneis is happening