Oidation Of Acetyl Coa By The Tricarboxylic Acid Cycle

Front 1

What vitamin precursor is CoA associated with?

Back 1

B5... pantothenic acid

Front 2

How many carbons are added with Acetyl-CoA... and how do you end up with 6-carbon needed for citrate?

Back 2

two + 4 from oxaloacetate = 6

Front 3

Are there many TCA related genetic enzyme abnormalities?

Back 3

No

Front 4

Describe the process of pyruvate being converted to acetyl CoA:
a. reactants and enzymes
b. products
c. ∆G°

Back 4

a.Reactants:
• pyruvate
• NAD+
• CoASH
• pyruvate dehydrogenase

b.Products:
• acetyl CoA
• NADH
• CO2

c. c. ∆G° = -8.0 kcal/mol
.

Front 5

Describe the pyruvate dehydrogenase complex.
a. number of subunits
b. number of dif enzmes
c. number of regulatory proteins.
d. number of coenzymes
.

Back 5

a. number of subunits =60
b. number of dif enzmes = 3
c. number of regulatory proteins = 2
d. number of coenzymes =5
.

Front 6

Name the first 3 enzymes of the pyruvate dehydrogenase complex and
b.their numbers and
c. their respective roles.
.

Back 6

1. E1
a. Pyruvate dehydrogenase component (pyruvate decarboxylate)
b. 24 monomers
c. removes CO2 (carboxyl)

2. E2
a. Lipoamide redutase transacetylase (w/ TPP a temporary acetyl carrier)
b. 8 trimers
c. transfer the acetyl group to the HSCoA to make acetyl CoA.

3. E3
a. Dihydrolipoyl dehydrogenase
b. 12 monomers
c. a. Dihydrolipoyl dehydrogenase
b. 12 monomers
c. reoxidizes the transacetylase (recycle) in the process NADH is made and delivered to ETC.

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Front 7

What vitamin (and its deriviative) is associated with pyruvate decarboxylase, and as such the acetyl group is attached to it?
.

Back 7

B1, Thiamine pyrophosphate (more specifically, the thiazolium ring)
.

Front 8

What causes Wernicke-korsakoff Syndrome?
.

Back 8

ability to uptake B1 is inhibited and poor diet... it's not because ethanol is a poor fuel.
.

Front 9

What reoxidizes lipoamide reductase? and how?

Back 9

dihydrolipoyl dehydrogenase reduces NAD+ to NADH, so in the process it reoxidizes lipoamide.
.

Front 10

Describe citrate synthesis:
a. reactants
b. products
b. enzymes
c. ∆G° = ?

Back 10

a. reactants
• oxaloacetate,
• acetyl CoA
• water

b. Products:
• citrate
• HSCoA
• H+

c. enzyme: Citrase synthase

d. ∆G° = -7.7 kcal/mol
.

Front 11

Describe Isocitrate synthesis: (note: cis-aconitate is an intermediate)
a. reactants
b. products
b. enzymes
c. ∆G° = ?

Back 11

a. reactants
• citrate

b. Products:
• isocitrate

c. enzyme: aconitase

d. ∆G° = 1.5 kcal/mol (driven by the favorable next rxn that pulls txn to the right).
.

Front 12

Describe ∂-ketoglutarate synthesis:
a. reactants
b. products
b. enzymes
c. ∆G° = ?

Back 12

a. reactants
• Isocitrate
• NAD+

b. Products:
• ∂-ketoglutarate
• NADH
• CO2

c. enzyme: isocitrate dehydrogenase

d. ∆G° = -5.3 kcal/mol
.

Front 13

Describe Succinyl CoA synthesis:
a. reactants
b. products
b. enzymes
c. ∆G° = ?

Back 13

a. reactants
• ∂-ketoglutarate
• NAD+
• CoASH

b. Products:
• succinyl CoA
• NADH + H+
• CO2

c. enzyme: ∂-ketoglutarate dehydrogenase

d. ∆G° = -8.0 kcal/mol.
.

Front 14

Describe Succinate synthesis:
a. reactants
b. products
c. enzymes
d. ∆G° = ?
e. What does this rxn compete with?
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Back 14

a. reactants
• Succinyl CoA
• GDP

b. Products:
• Succinate
• GTP
• CoASH

c. enzyme: Succinyl-CoA synthase

d. ∆G° = -0.7 kcal/mol.
e. the rxn where the ketone body, acetoacetate is activated to be converted acetoacetyl CoA... however in the end succinate is still produced, but without GTP.
.

Front 15

What step in the TCA cycle is CoA needed, without which the TCA cycle would stop? (not acetyl CoA)

Back 15

∂-ketoglutarate to Succinyl CoA rxn.

Front 16

Functionally, what is ∂-ketoglutarate dehydrogenase similar to?

Back 16

Pyruvate dehydrogenase

Front 17

Which TCA oxidation rxn, does not produce CO2 but FADH2 in its place?

Back 17

Succinate to Fumarate

Front 18

Describe Fumarate synthesis:
a. reactants
b. products
c. enzymes... what is special here?
d. ∆G° = ?
e. What is special about this oxidative TCA rxn?
.

Back 18

a. reactants
• Succinate
• FAD

b. Products:
• Fumarate
• FADH2
• NOTE: NO CO2 PRODUCED HERE!!!

c. enzyme: Succinate dehydrogenase: attached to the inner mitochondrial membrane (matrix side).

d. ∆G° = -0 kcal/mol.

Front 19

Describe Malate synthesis:
a. reactants
b. products
c. enzymes
d. ∆G° = ?

.

Back 19

a. reactants
• Fumarate
• H2O

b. Products:
• Malate

c. enzyme: Fumarase

d. ∆G° = 0 kcal/mol.

Front 20

Describe Oxaloacetate synthesis:
a. reactants
b. products
c. enzymes
d. ∆G° = ?
.

Back 20

a. reactants
• Malate
• NAD+

b. Products:
• Oxaloacetate
• NADH
• NO CO2 PRODUCED HERE!!!

c. enzyme: Malate dehydrogenase.

d. ∆G° = +7.1 kcal/mol... very positive.


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Front 21

What are the three profoundly exergonic reaction, and thus highly regulated rxns?
.

Back 21

• Citrate synthase (∆G° = -7.7 kcal/mol)
• isocitrate dehydrogenase (∆G° = -5.3 kcal/mol)
• ketogluterate dehydrogenase (∆G° = -8.0 kcal/mol)
.

Front 22

What is the overall ∆G° for TCA

Back 22

∆G° = - 13.1 kcal/mol

Front 23

What percentage of energy available from the oxidation of acetyl CoA is capture in chemical form?
.

Back 23

90% ( 206 kcal ÷ 228 kcals... in NADH, FADH2 and GTP)

Front 24

What pulls the malate to oxaloacetate rxn?

Back 24

Oxaloacete being converted to citrate.

Front 25

What are the 4 key Kreb's enzymes that are regulate in the TCA cycle?

Back 25

1. citrate synthase

2. isocitrate dehydrogenase

3. ∂-ketoglutarate dehydrogenase

4. pyruvate dehydrogenase
.

Front 26

What are 2 ways citrate synthase regulation can inhibit the TCA cycle?.

Back 26

1. product inhibition: [citrate] is to high
2. Allosteric control:
a. via ATP/ADP... ratio of 1 (being best) inhibits citrate synthase.
b. Also NADH/NAD ratio
.

Front 27

How is the ∂-ketoglutarate dehydrogenase rxn (∂-ketoglutarate to succinyl CoA) involved in TCA regulation?
.

Back 27

∂-ketoglutarate dehydrogenase undergoes product inhibition: these products include excess succinyl CoA and NADH.
.

Front 28

What are the 2 ways the pyruvate dehydrogenase rxn (pyruvate to acetyl CoA) is involved in TCA regulation?
.

Back 28

Pyruvate dehydrogenase is ihibited by:

a. Product inhibition:
• acetyl CoA
• NADH

b. Allosteric inhibition: ATP
.

Front 29

What are the two proteins that inhibit pyruvate dehydrogenase and how do they function?

Back 29

a. Kinase:
• [NADH an acetyl CoA]high --> kinase is allosterically acitve --> phosphorylated pyruvate dehydrogenase is inactive.

b. Phosphatase:
[NAD and CoASH] are high --> Phosphatase is allosterically activated --> removes phosphate from pyruvate dehydrogenase --> pyruvate dehydrogenase is activated.
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