Question

What are the three reactions that go from glucose-6-phosphate to the linear glycogoen chain? Explain each reaction

Answer 1

The steps involved in conversion of glucose-6-phosphate to the linear glycogen chain are

1) Conversion of glucose-6-phosphate to glucose-1-phosphate.

2)Attachment of UTP to glucose-1-phosphate to form uridine diphosphate glucose UDP-glucose.

3)Attachment of UDP-glucose to glycogen primer and glycogen synthesis.

step-1:Glucose-6-phosphate is converted to glucose-1-phosphate by the enzyme phosphoglucomutase passing through a obligatory intermediate glucose-1,6-diphosphate.

Glucose-6-phosphate + enzyme-p Glucose-1,6-diphosphate+enzymeGlucose-1-phosphate+enzyme-p

step-2:Glucose-1-phosphate react with uridine triphosphate (UTP)to form activated nucleotide uridine diphosphate glucose (UDP-Glucose) by the enzyme glucosepyrophophorylase.

UTP+ Glucose-1-phosphate UDP-Glc+PPi (enzyme glucopyrophosphorylase)

step-3:A small fragment of pre-exisisting glycogen must act as primer (also called as glycogenin) to initiate glycogensynthesis. The glycogenin can accept glucose from UDP-Glucose.

The hydroxyl group of amino acid tryosine of glycogenin is the site at which initial glucose unit is attached, the enzyme glycogen initiator synthase transfers first glucose molecule to glycogenin. Then the glycogenin itself takes up the glucose residues to form a fragment of primer which serves as a acceptor for rest of glucose molecules. Glycogen synthase catalyses the formation linear unbranched glycogen molecule by forming alpha1,4 linkage.

UDP-Glucose+(glucose)_n (glucose)_n+1  (enzyme glycogen synthase).