Glycogen Synthesis

Glycogen Synthesis is thermodynamically

• unfavorable from G1P

Glycogen Synthesis requires 3 enzymes

• UDP-glucose pyrophosphorylase

• Glycogen Synthase

• Glycogen Branching Enzyme

UDP-glucose Pyrophosphorylase

• activates glucosyl units

Uridine Diphosphate Glucose (UDPG) has a delta G around 0 when

• activated

• donates glucosyl unit to the growing chain

Inorganic Phosphotase creates an overall delta g (-) through

• subsequent exergonic hydrolysis of PPi

Glycogen Synthase

• extends glycogen chain

• transfers glucosyl unit of UDPG to C4-OH of the NON reducing ends

Glycogen Synthase transfer of glycosyl unit of UDPG to non reducing ends OH group forms a ?

• alpha(1 →4) glycosidic bond

After transfer UDPG is released with ?

• 1 glucose with one more unit than it had before

• UTP cleaved to UDP/glucose residue incorporated into glycogen

Glycogen Synthesis Cost

• energetic price= UTP

UTP

• required to activate glucose unit before added to glycogen subunit

UTP is replenished by?

• ATP through phosphoryl-transfer reaction

Phosphoryl Transfer Reaction of UTP and ATP mediated by?

• Nucleoside Diphosphate Kinase

Glycogen synthase cannot just link together 2 glucose residues it solely

• extends already existing alpha(1→4) linked glucan chain

1st Step of Glycogen Synthesis

• Glycogenin acts as a glucosyltransferase

Glycogenin as a glucosyltransferase

• attaches glucose residues donated by UDPG to OH group of TYR 194

Glycogenin extension of glucose chain up to how many residues?

• 7 additional UDPG-donated glucose residues

Glycogenin helps with

• formation of glycogen primer

• glycogen synthase commences to extend the primer

Glycogen primer made by glycogenin made up of how many glucose subunits

• 6 glucose subunits

Each Glycogen is associated with:

• 1 glycogenin

• 1 glycogen synthase

Glycogen Synthase only generates alpha(1→4) which yields

• alpha amylose

alpha amylose releases how many glycogen segments at a time?

• one segment at a time at reducing end (1)

Glycogen Branching Enzyme

• transfers 7 residue glycogen segments by amylo-(1,4 → 1,6)-tranglycosylase from chain end of the same or another glycogen chain

Transferred segments of glycogen branching enzyme must come from a chain with how many residues ?

• at least 11 residues

How far do branch points need to be away from each other?

• at least 4 residues away

Branching pattern is optimized by:

• efficiency of storage and mobilization of glucose