TCA Cycle and Oxidative Phosphorylation Flashcards
What are the prosthetic groups for the enzymes of the Pyruvate dehydrogenase complex?
E1 - TTP
E2 - lipamide
E3 - FAD
What happens in the first part of the PDH complex at E1?
Pyruvate with TPP is decarboxylated to hydroxyethyl-TPP
W/ CO2 as a product.
What happens in the second part of the pyruvate dehydrogenase complex at E2?
E2 with help of the movable lipoamide oxidizes Hydroxyethyl-TPP to an acetyl group. The acetyl group is transferred to lipoamide.
Makes a Acetyl lipoamide - which has an energy rich thioester bond
- > linked at a lysine at E1.
- > transfer catalyzed by E1
What happens in the third part of the pyruvate dehydrogenase complex at E3?
The lipoamide-acetyl group swings to a deep part of E2, the acetyl group is transferred to a CoA, a processed catalyzed by E2.
E3 oxidezes the remaining dihydroamide back to a lipoamide. This transfers to a FAD+ and then to NAD+
FAD is the prosthetic group
Acetyl-CoA the second product is made out of this.
Get NADH from this step
What regulates the PDH complex?
high [Acetyl CoA] inhibits E2
Allosterically regulated by reverse phosphorylation -> similar to glycogen synthase
Products increase the phosphorylation of PDH
Accumulation of ADP and pyruvate activates phosphatases.
The first step of the CAC catalyzed by citrate synthase mainly includes which events?
The condensation of oxaloacetate and the acetyl group from the Acetyl-CoA giving citrate
After citrate is formed in the TCA cycle what is the next step?
The citrate molecule is isomerized to isocitrate to prepare for the first decarboxylation event.
Isocitrate dehydrogenase catalyzed what step of the TCA cycle?
Isocitrate decarboxylation to a-ketogluterate with the release of a CO2 and a NADH
Redox
Rate limiting
Allosteric stimulated by ADP
After the first decarboxylation event a-ketogluterate dehydrogenase catalyzes what?
Release of NADH and CO2 and formation of Succinyl-CoA.
This step is similar to PDH because both are decarboxylations of an a-ketoacid and create a thioester bond with a CoA
What’s unique about the succinyl-CoA synthetase step of the TCA cycle?
It is the only step of TCA that directly gives off a high energy compound, GTP
And Succinate
After the formation of Succinate from Succinyl-CoA in the TCA cycle, what energy molecule is release and the product of succinate dehydrogenase?
The redox rxn between succinate and fumerate by succinate dehydrogenase gives off a FADH2
No change in carbon number between the molecules.
It is then turned into Malate by fumerase
Fumerase turns Fumerate into Malate. What happens next in the TCA cycle?
Malate into Oxaloacetate by malate dehydrogenase, releasing a NADH
At this point the cylce is ready to restart.
Not a favorable reaction. The reaction is driven by the use of the products, oxaloacetate and NADH
What doess it mean if there is a build up of NADH?
It means that the CAC isnt running. The excess of NADH means a build up of potential energy.
The Citric Acid Cycle is regulated at PDH, isocitrate dehydrogenase, and a-ketogluturate dehydrogenase.
The PDH is stimulated with ADP and pyruvate and downregulated by ATP, acetyl CoA and NADH
Isocitrate dehydrogenase is allosterically stimulated by ADP and negatively regulated by ATP and NADH
A-ketogluturate dehydrogenase is only negatively regulated by ATP, succinylcholine CoA and NADH.
-> similar to PDH, also allosterically inhibited by it’s products.
Inhibiting the cycle at isocitrate dehydrogenase leads to a build up of citrate. This citrate goes back and inhibits what other metabolic processes?
What else can citrate go?
Glycoylsis at phosphofructokinase.
Citrate can be used to make fatty acids and sterols.
