Chapter 10: The Citrate Cycle Flashcards

1
Q

How does the citrate cycle capture energy

A

Redox reactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are two biomolecules that the citrate cycle generates?

A
  • NADH and FADH2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is the Citrate cycle so important?

A

It is central to aerobic metabolism and ATP production

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the primary function of Acetyl CoA? What does each Citrate cycle yield.

A
  • The primary function is to oxidize acetyl CoA

Each cycle yields:
- Transfer of 8 electrons
- Generates 3 NADH
- Generates 1 FADH2
- 1 GTP (ATP equivalent)
- Each cycle results in production of 10 ATP
- Mostly via oxidative phosphorylation of 3NADH and 1 FADH2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What converts Pyruvate into acetyl-CoA?

A

Pyruvate dehydrogenase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What five coenzymes are required for the pyruvate dehydrogenase complex?

A
  • NAD+
  • FAD
  • CoA
  • Thiamine pyrophosphate (TPP)
  • Alpha-lipoic acid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What part of NAD+ and NADP+ is reduced?

A

Nicotinamide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is NAD+ derived from?

A

Niacin (vitamin B3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is FAD derived from?

A

Riboflavin (vitamin B5)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is CoA derived from?

A

Vitamin B5
- Generated by Pantothenic acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is Thiamine pyrophosphate (TPP) derived from?

A

Vitamin B1
- Required for pyruvate dehydrogenase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does α-lipoic acid do?

A
  • Provides reactive disulfide that participates in redox reactions
  • Accepts and transfers acetyl group to CoA
  • Not a vitamin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the five steps in pyruvate dehydrogenase?

A

1.Pyruvate binds and is decarboxylated causing the formation of hydroxyethyl-TPP
2. Acetyl group transferred to lipoamide
3. Acetyl group transfered to CoA
4. Dihydroxylipoamide oxidized to lipoamide
5. FAD oxidized forming FADH2 which can reduce NAD+ to NADH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the general structure of PDH protein complex

A
  • 22 E1 subunits
  • 60 E2 subunits
  • 6 E3 subunits
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does Arsenic affect Pyruvate dehydrogenase?

A
  • Irreversibly blocks catalytic activity of lipoamide-containing enzymes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the steps of E1, E2, and E3 in the ball and chain PDH

A
  1. E2 ball and chain move lipoamide domain between E1 and E2 catalytic site
  2. Acetyl group from TPP in E1 to the CoA substrate in the E2 catalytic site
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are negative and positive regulators of PDH?

A

Positive:
- NAD+
- CoA
- ADP

Negative:
- NADH
- Acetyl- CoA
- ATP

18
Q

How many reactions are in the citrate cycle?

19
Q

How favorable or unfavorable are the equations in the citrate cycle?

A
  • 3 reactions have a large -ΔG°’ and thus are key regulators
  • 4 reactions have a ΔG°’ close to 0
  • 1 reaction has a large +ΔG°’
20
Q

What happens in step 1 of the citrate cycle?

A

Reaction: Condensation
Enzyme: Citrate synthase
Reactants: Oxaloacetate, Acetyl-CoA, and H2O
Product: Citrate

(Highly Favorable)

21
Q

What is the mechanism behind citrate synthase?

A
  1. Asp375 deptrotenates acetyl-CoA -> enolate intermediate (stabilized by H bond of His274)
  2. Nu attack by enolate in on oxaloacetate -> citryl-CoA + deprotonation of His320
  3. Water is added which helps hydrolyze citryl-CoA thioester
22
Q

How does conformation affect binding in citrate synthase?

A
  • Open conformation promotes oxo binding
  • Closed conformation promotes acetyl-CoA binding
  • Prevents acetyl-CoA thioester hydrolysis
23
Q

What is step 2 in the citrate cycle?

A

Reaction: dehydration-hydration
Enzyme: Aconitase
Reactants: Citrate and H2O
Product: (intermediate cis-aconitate) Isocitrate

24
Q

What is the function of the Fe-S cluster enzyme?

A
  • Facilitates the removal of OH group from citrate
25
What is fluoroacetate and what does it do?
- Converted to Fluoroacetyl-CoA then Fluorocitrate - Potent inhibitor of Aconitase
26
What is step 3 in the citrate cycle?
Reaction: Oxidative decarboxylation Enzyme: Isocitrate dehydrogenase Reactants: Isocitrate, NADP+, and H+ Product: NADPH, (intermediate oxalosuccinate), CO2, and alpha ketoglutarate
27
Which step is the rate limiting reaction in the citrate cycle?
Step 3 or isocitrate dehydrogenase
28
What are positive and negative effectors of step 3 in the Citrate cycle?
Positive: - ADP and CA2+ Negative: - ATP and NADH
29
What is step 4 in the citrate cycle?
Reaction: Decarboxylation Enzyme: α-Ketoglutarate Dehydrogenase (E1, E2, E3) Reactants: α-Ketoglutarate, CoA, and NAD+ Product: CO2, NADH +H+, and Succinyl-CoA (Same reaction as Pyruvate dehydrogenase) (Energetically favorable)
30
What is step 5 in the citrate cycle?
Reaction: Substrate level phosphorylation Enzyme: Succinyl-CoA synthetase Reactants: Succinyl-CoA, Pi, and GDP Product: CoA, GTP, and Succinate
31
What is step 6 in the citrate cycle?
Reaction: Oxidation Enzyme: Succinate dehydrogenase Reactants: Succinate and FAD Product: FADH2 and Fumarate (part of ETC)
32
What is step 7 in the citrate cycle?
Reaction: Hydration Enzyme: Fumarase Reactants: Fumarate, OH-, and H+ Product: (carbanion intermediate) and Malate (stereospecific L-isomer)
33
What is step 8 in the citrate cycle?
Reaction: Oxidation Enzyme: Malate dehydrogenase Reactants: Malate and NAD+ Product: NADH + H+ and Oxaloacetate
34
What does one citrate cycle produce
- One cycle: - 3 NADH - 1 FADH2 - 1 GTP - Equals 10 ATP - 2 carbons enter as Acetyl-CoA - Leave cycle via decarboxylation as CO2 - Not same carbons as Carbons eliminated in step 1
35
What are the three main regulatory regulatory enzymes in the citrate cycle?
- Citrate Synthase - Isocitrate synthase - α-ketoglutarate dehydrogenase
36
How can culture conditions affect the citrate cycle? How can citrate export increase?
- Citrate cycle can be inhibited by culture conditions - Inhibitions of Citrate lyase results in increase citrate export
37
The citrate cycle is an ________ pathway.
Amphibolic (both anabolic and catabolic
38
What is an anaplerotic reaction?
A reaction that replenishes Citrate cycle intermediates from other metabolic pathways Examples: Pyruvate carboxylase Requires biotin
39
What is biotin?
A CO2 carrier
40
What does phosphoenolpyruvate carboxylase do?
Replenish Oxaloacetate
41
What are the Two main functions of the citrate cycle?
Function 1 - Oxidize acetyl-CoA - Yields 3 NADH, 1 FADH2, 1 GTP - Can produce 10 ATP Function 2 - Provides metabolites for other pathways - Amino acids - Heme - Fatty acids