FINAL EXAM CHAPTER 18 Preparing for the cycle Flashcards
Where is the reaction occurring?
Inside the matrix of a mitochondria
Under aerobic conditions what converts into Acetyl CoA and what is Acetyl CoA fuel for?
Pyruvate enters the mitochondria and converts into acetyl CoA
Acetyl CoA is the fuel for citric acid cycle
What does the pyruvate dehydrogenase complex do?
It oxidatively carboxylates pyruvate to form acetyl CoA
What are the three steps of the synthesis of acetyl CoA from pyruvate?
-decarboxylation
-oxidation
-transfer to CoA
What is the enzyme name, prosthetic group of E1 and what reaction is being catalyzed?
-Pyruvate dehydrogenase component
-TTP(prosthetic group)
Reaction catalyzed:
-Oxidative decarboxylation of pyruvate
What is the enzyme name , prosthetic group of E2 and what is the reaction being catalyzed?
-Dihydrolipoyl transacetylase
-Lipoamide
Reaction catalyzed:
Transfer of acetyl group to CoA
What is the enzyme name, prosthetic group of E3 and what is the reaction being catalyzed?
-Dihydrolipoyl dehydrogenase
-FAD
Reaction catalyzed:
Regeneration of the oxidized form of lipoamide
What happens at the decarboxylation step ?
=E1 catalyzes the decarboxylation. pyruvate combines with the ionized form of the coenzyme TPP
What is a lipoamide?
A coenzyme that is formed by vitamin lipoic acid attaching to a lysine residue in E2
What happens at the oxidation step?
The Hydroxyethyl group attached to TPP is oxidized to form an acetyl group while being simultaneously transferred to lipoamide.
Also the disulfide group of lipoamide is reduced to its disulfhydryl form in this reaction. The reaction is catalyzed by E1 and yields acetyl lipoamide
What happens at the transfer/formation of acetyl CoA step?
-E2 catalyzes the transfer of the acetyl group from acetyl -lipoamide to coenzyme A to form acetyl CoA
To participate in another reaction cycle what has to be done and what is this reaction catalyzed by?
Dihydrolipoamide must be oxidized
catalyzed by E3
What is the flexible lipoamide arms role?
it allows for rapid movement of substrates and products from one active site of the complex to another
What are the two principle fates of Acetyl CoA
-Metabolism by the citric acid cycle
-incorporation into fatty acids
What molecules stimulate and inhibit the complex
inhibit:ATP,Acetyl CoA,NADH
stimulate:ADP ,pyruvate
What does a kinase in the E1 do?
it goes through complex phosphorylates and inactivates E1.
What does a phosphatase do in E1?
removes the phosphate and thereby activates the enzyme
Where does the free energy get stored from the oxidation of pyruvate?
NADH and Acetyl CoA
Why is the thioester bond high energy /unstable?
Its because sulfur is bigger than oxygen and this causes less delocalization of sulfur lone pairs toward carbonyl carbon
