Ls4203_midsem_2016 please answer only question no.3. (1+2+2=5 marks) Time: 10 AM

Question

Ls4203_midsem_2016

please answer only question no.3. (1+2+2=5 marks)

Time: 10 AM to 10:55 AM Answer any four: I. How Isozymes give advantages in metabolism? Explain with example? How Insulin and Glucagon regulate the glycolysis and gluconeogenesis? 2+3-5 2. What will be the pathophysiological effecet of loss of function mutation of elycogen phosphorylase? How C-AMP regulate the activity of Glycogen phosphorylase? How blood glucose levels regulate the activity of Glycogen phosphorylase? 2+1.5+ 1.5-5 3. What is the function of Pyruvate Dehydrogenase complex (PDH)? Describe the role of each cofactors involved in the reaction catalyzed by the pyruvate dehydrogenase complex. What are the regulations of activity of pyruvate dehydrogenase complex? 1+2+2#5 4. Why animal could not survive with only on sneetate as soie carbon sourec? How plant and microbes can survive with acetate as sole carhon source? In aduli animat if the food is only lipid: what will be the consequences? What is role of Perosisome in fatty acid oxidation? 1+2+1+1-5 5. Explain why referring to the Calvan gycte as the "dad reactions ot photosynthesis is

Explanation / Answer

Pyruvate dehydrogenase is actually a complex of enzymes carrying out multiple reactions like

- converts pyruvate to acetyl-CoA
- irreversible, PDH cannot be used to convert acetyl-CoA into pyruvate or glucose

This large complex requires multiple cofactors and coenzymes.

Role of each cofactor

TPP: thiazolium ring adds to alpha carbon of pyruvate, then stabilizes the resulting carbanion by acting as an electron sink
Lipoic acid: oxidizes pyruvate to level of acetate (acetyl-CoA) and then activates acetate as a thioester
CoA-SH: activates acetate as the thioester.
FAD: oxidizes lipoic acid
NAD+: oxidized FAD

Regulation of Pyruvate dehydrogenase

The pyruvate dehydrogenase complex is managed by covalent alteration of the primary enzyme, pyruvate dehydrogenase (PDH). Pyruvate dehydrogenase kinase inactivates PDH by phosphorylation with ATP. Reactivation is accomplished by the activity of pyruvate dehydrogenase phosphatase. Both of these administrative enzymes are controlled:

PDH kinase is stimulated by NADH and acetyl-CoA. It is inhibited by pyruvate.

PDH phosphatase is stimulated by Ca++ and insulin.

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