🖊️
Midterm 3
Lecture 18: Preparations for the cycle
Questions:
What is important about the process of glycolysis?
10 reactions
2 involve energy investment
3 reap energy in form of NADH and ATP
What happens if there’s no oxygen available in glycolysis?
Pyruvate converted to ethanol or lactate - helps regenerate NAD+ needed for
conversion of G3P to 1,3 BPG
What happens if there is oxygen available in glycolysis?
Citric acid cycle can be used - pyruvate to Acetyl CoA that can come from
fatty acids, glycolysis, and amino acids
What is done with the 2C Acetyl unit produced?
Reacting it with a 4C molecule to yield a 6C molecule, lose 2 CO2 and
generate high transfer potential electrons and little bit of ATP, regenerate 4C
acceptor
What is the carrier for the acetyl group?
Coenzyme A
What is the cell’s metabolic decision?
Whether it will oxidize glucose to CO2 or save some of it as 3C compounds
like DHAP, G3P, or pyruvate
When would you want to oxidize C into CO2?
When we need ATP, or else it is better to save it as a 3C compound
Midterm 3 1
, Where does the citric acid cycle occur?
Mitochondrial matrix
What is pyruvate dehydrogenase?
Enzyme in mitochondrial matrix that decarboxylates pyruvate into Acetyl CoA
and allows it to go from cytosol to matrix
Is pyruvate dehydrogenase simple?
No it contains 3 enzymatic activites and 5 coenzymes
What is the net reaction for citric acid cycle?
Pyruvate + CoA + NAD+ → Acetyl CoA + CO2 + NADH + H+
What is the acetyl part?
CH3-C=O
What cofactors are involved in the pyruvate DH reaction?
1. Acetyl CoA
2. NAD+
What are Coenzyme A and NAD known as?
Stoichiometric coenzymes - participating in reaction and need to be able to
regenerate them
What 3 enzymes are involved in the pyruvate DH complex?
1. Pyruvate dehydrogenase(E1) - decarboxylation of pyruvate, 24 chain, TPP
prosthetic group
2. Dihydrolipoyl transacetylase(E2) - transfer of acetyl group to CoA, 24
chain, lipoamide prosthetic group
3. Dihydrolipoyl dehydrogenase(E3) - regeneration of oxidized form of
lipoamide, 12 chain, FAD prosthetic group
What are the prosthetic groups known as?
Catalytic coenzymes
What are the 3 steps in synthesis of Acetyl CoA?
Midterm 3 2
, Decarboxylation, oxidation, and transfer to CoA
What are the dietary sources of the 3 catalytic coenzymes?
1. TPP - nuts, fish, beans
2. Lipoamide - green plants, foods rich in mitochondria
3. FAD - milk, eggs, almonds
What happens in the decarboxylation step?
Pyruvate combines with ionized form of coenzyme thiamine
pyrophosphate(TPP)
What happens in the oxidation step?
2C fragment is oxidized and transferred to lipoamide to form acetyllipoamide
on E2 in a reaction catalyzed by E2, regenerate carbanion of TPP
How is dihydrolipoamide formed?
Attachment of vitamin lipoic acid to a lysine residue in another enzyme in
complex, E2
What is the transfer and formation step of Acetyl CoA?
E2 catalyzes transfer of acetyl group from acetyllipoamide, lipoamide arm, to
coenzyme A to form acetyl CoA, regenerate lipoamide
How do we regenerate the acceptor?
Using FAD
What is important about catalytic coenzymes?
Have to be reset for next substrate, dyhydrolipoamide must be reoxidized
What is important about the 2 catalytic enzymes?
Structurally integrated, lipoamide arm allows rapid movement of substrates
and products from one active site of complex to another
What is important about the formation of acetyl CoA from pyruvate?
Irreversible in animal cells
What are the 2 fates of acetyl CoA?
Midterm 3 3
, 1. Metabolism by citric acid cycle
2. Incorporation into fatty acids
What is the key site of regulation?
Enzyme E1, kinase associated with the complex phosphorylates and
inactivates E1
How is a phosphatase associated with the complex?
Removes phosphate and activates the enzyme
What else is PDH regulated by?
Energy charge
What activates and inhibits the complex?
ADP and pyruvate activate
ATP, Acetyl CoA, and NADH inhibit
Why is a build up of acetyl CoA bad?
It usually gets used up because it’s a cycle so if there’s built up that means
you’re not drawing it through the reaction
What does post translational modification of PDH do?
Alters activity, phosphorylation inactivates, can be activated hormonally by
insulin in tissues capable of fatty acid synthesis
What happens if you have inactivate PDH?
Kinase uses up ATP, kinase requires a fairly high amount of ATP
What happens as there is enhanced PDH kinase activity?
Pyruvate processed to lactate which can cause lactic acidosis, production of
lactate in presence of oxygen is a characteristic of cancer cells due to
stimulation of PDH kinase
What happens with thiamine deficiency?
Results in insufficient PDH activity → NM pathologies like Berberi
How can PDH activity be affected by mercury and aresenite?
Midterm 3 4
Midterm 3
Lecture 18: Preparations for the cycle
Questions:
What is important about the process of glycolysis?
10 reactions
2 involve energy investment
3 reap energy in form of NADH and ATP
What happens if there’s no oxygen available in glycolysis?
Pyruvate converted to ethanol or lactate - helps regenerate NAD+ needed for
conversion of G3P to 1,3 BPG
What happens if there is oxygen available in glycolysis?
Citric acid cycle can be used - pyruvate to Acetyl CoA that can come from
fatty acids, glycolysis, and amino acids
What is done with the 2C Acetyl unit produced?
Reacting it with a 4C molecule to yield a 6C molecule, lose 2 CO2 and
generate high transfer potential electrons and little bit of ATP, regenerate 4C
acceptor
What is the carrier for the acetyl group?
Coenzyme A
What is the cell’s metabolic decision?
Whether it will oxidize glucose to CO2 or save some of it as 3C compounds
like DHAP, G3P, or pyruvate
When would you want to oxidize C into CO2?
When we need ATP, or else it is better to save it as a 3C compound
Midterm 3 1
, Where does the citric acid cycle occur?
Mitochondrial matrix
What is pyruvate dehydrogenase?
Enzyme in mitochondrial matrix that decarboxylates pyruvate into Acetyl CoA
and allows it to go from cytosol to matrix
Is pyruvate dehydrogenase simple?
No it contains 3 enzymatic activites and 5 coenzymes
What is the net reaction for citric acid cycle?
Pyruvate + CoA + NAD+ → Acetyl CoA + CO2 + NADH + H+
What is the acetyl part?
CH3-C=O
What cofactors are involved in the pyruvate DH reaction?
1. Acetyl CoA
2. NAD+
What are Coenzyme A and NAD known as?
Stoichiometric coenzymes - participating in reaction and need to be able to
regenerate them
What 3 enzymes are involved in the pyruvate DH complex?
1. Pyruvate dehydrogenase(E1) - decarboxylation of pyruvate, 24 chain, TPP
prosthetic group
2. Dihydrolipoyl transacetylase(E2) - transfer of acetyl group to CoA, 24
chain, lipoamide prosthetic group
3. Dihydrolipoyl dehydrogenase(E3) - regeneration of oxidized form of
lipoamide, 12 chain, FAD prosthetic group
What are the prosthetic groups known as?
Catalytic coenzymes
What are the 3 steps in synthesis of Acetyl CoA?
Midterm 3 2
, Decarboxylation, oxidation, and transfer to CoA
What are the dietary sources of the 3 catalytic coenzymes?
1. TPP - nuts, fish, beans
2. Lipoamide - green plants, foods rich in mitochondria
3. FAD - milk, eggs, almonds
What happens in the decarboxylation step?
Pyruvate combines with ionized form of coenzyme thiamine
pyrophosphate(TPP)
What happens in the oxidation step?
2C fragment is oxidized and transferred to lipoamide to form acetyllipoamide
on E2 in a reaction catalyzed by E2, regenerate carbanion of TPP
How is dihydrolipoamide formed?
Attachment of vitamin lipoic acid to a lysine residue in another enzyme in
complex, E2
What is the transfer and formation step of Acetyl CoA?
E2 catalyzes transfer of acetyl group from acetyllipoamide, lipoamide arm, to
coenzyme A to form acetyl CoA, regenerate lipoamide
How do we regenerate the acceptor?
Using FAD
What is important about catalytic coenzymes?
Have to be reset for next substrate, dyhydrolipoamide must be reoxidized
What is important about the 2 catalytic enzymes?
Structurally integrated, lipoamide arm allows rapid movement of substrates
and products from one active site of complex to another
What is important about the formation of acetyl CoA from pyruvate?
Irreversible in animal cells
What are the 2 fates of acetyl CoA?
Midterm 3 3
, 1. Metabolism by citric acid cycle
2. Incorporation into fatty acids
What is the key site of regulation?
Enzyme E1, kinase associated with the complex phosphorylates and
inactivates E1
How is a phosphatase associated with the complex?
Removes phosphate and activates the enzyme
What else is PDH regulated by?
Energy charge
What activates and inhibits the complex?
ADP and pyruvate activate
ATP, Acetyl CoA, and NADH inhibit
Why is a build up of acetyl CoA bad?
It usually gets used up because it’s a cycle so if there’s built up that means
you’re not drawing it through the reaction
What does post translational modification of PDH do?
Alters activity, phosphorylation inactivates, can be activated hormonally by
insulin in tissues capable of fatty acid synthesis
What happens if you have inactivate PDH?
Kinase uses up ATP, kinase requires a fairly high amount of ATP
What happens as there is enhanced PDH kinase activity?
Pyruvate processed to lactate which can cause lactic acidosis, production of
lactate in presence of oxygen is a characteristic of cancer cells due to
stimulation of PDH kinase
What happens with thiamine deficiency?
Results in insufficient PDH activity → NM pathologies like Berberi
How can PDH activity be affected by mercury and aresenite?
Midterm 3 4
