46) The synthesis of new glycogen molecules are initiated by the homodimeric pro

Question

46) The synthesis of new glycogen molecules are initiated by the homodimeric protein that catalyres the addition of 8 hcose molecules to a tyrony residue in the protein. Thun, elycopen molecules are actually a type of slycosylated protein a) Glucogenin c) Amylogenin d) Glycogen synthase ) Branching entyme 47) ln mammalian cells the synthesis of fatty acids is catalyzed by a mulkifunctional protein a) Acetyl CoA Carboxylase b) Carntine acyltransferase c) Fatty acid synthase d) Bketoacyl synthetase e) Acyl carrier protein 48) Fatty acid synthesis can be divided into 3 stages: Stage 1. Export of acetyl CoA from the mitochondria, Stage 2: Synthesis of malonyl CoA, and Stage 3 a) Import of acetyl CoA into mitochondria b) Export of acetyl CoA from the mitochondria c) Import of acyl CoA into cells from extracellular sources d) Export of malonyl CoA from the mitochondria e) Synthesis of palmitic acid. 49) Phosphatidic acid is a precursor for the lipid class(es): a) Triacylelycerides b) Sphingolipids c)Glycerophospholipids d) A and B e) A and C 50) The committed and regulated step of cholesterol synthesis is the enzyme which is an important target for a class of drugs called statins than can dramatically reduce circulating blood cholesterol and profoundhy reduce the incidence of heart attacks and stroke. a) HMG-CoA synthase b) HMG-CoA reductase c) Acetyl-CoA acetyltransferase d) Squalene synthase e) Dehydrocholesterol reductase Page 11 MCELLBI X105 Form A

Explanation / Answer

46. The answer is glycogenin.

A small fragment of pre-existing glycogen must act as a “Primer” (also called GLYCOGENIN) to initiate glycogen synthesis. The Glycogenin can accept glucose from UDP-Glc.

The hydroxyl group of the amino acid tyrosine of Glycogenin is the site at which the initial glucose unit is attached. the enzyme Glycogen initiator synthase transfers the first molecule of Glucose to Glycogenin.

Then glycogenin it self takes up a for glucose residues to form a fragment of primer which serves as an acceptor for the rest of the glucose molecules.

47.In mammalas fatty acid synthase is involved in the formation of fatty acids.

48.The last step is formation of palmitic acid which shifts the equilibrium towards the monomer formation.

49. Phosphatidic acid is precursor for the formation of triacylglycerols and glycerophospholipids.

50.HMG-CoA reductase is a rate limiting step in cholesterol synthesis

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