Question

Glycogenin also elongates the primer to about ___ glucose residues- then it can be a substrate for Glycogen synthase to add residues to it

Answer 1

Glycogen synthesis starts with glycogenin, which adds about 8 glucose residues as a primer. Glycogen synthase then adds glucose units to elongate the chain to about 10 to 12 residues before branching occurs, allowing for a more soluble and space-efficient glycogen polymer that serves as a key energy storage molecule in cells.

Step-by-step explanation:

Glycogenin Primer Elongation and Glycogen Synthesis

Glycogen synthesis, or glycogenesis, starts with the priming activity of glycogenin, which auto-glucosylates itself using UDP-glucose to add approximately 8 glucose residues. This self-glucosylation forms the primer for subsequent elongation by glycogen synthase, the main enzyme responsible for glycogen synthesis. Glycogen synthase extends the primer by adding more glucose units through α-1→4 glycosidic bonds, forming a linear chain of 10 to 12 glucose residues before the branching enzyme, or glycosyl transferase, introduces branches within the glycogen molecule.

The branching enzyme transfers a segment of this linear chain to create another chain, attaching it with a α-1→6 glycosidic linkage. This creates branching points and significantly increases the solubility and space-efficiency of glycogen within cells. These steps continue in a cycle to build up a glycogen polymer, which can subsequently be broken down by glycogen phosphorylase during glycogenolysis to release glucose when energy is needed by the body.