Glycogen

Glycogen (Definition and Structure)

Glycogen is a glucose polymer. Glucose units can be connected by bonds between carbon one and four, and carbon one and six.

Here is a diagram showing a large molecule of glycogen. Notice the many branches found in this structure due to the two different ways glucose units can be connected. Each empty circle represents one molecule of glucose.

At the center of the glycogen molecule is a protein called glycogenin.

Glucose is stored as glycogen. Glycogen synthesis adds individual glucose molecules to create glycogen. Glycogen breakdown removes individual glucose units that can then be used for metabolic processes.

how is glucose connected

Glucose units can be connected by bonds between carbon one and four, and carbon one and six.

glycogen characteristics

Glycogen is a glucose polymer.

At the center of the glycogen molecule is a protein called glycogenin.

Glucose is stored as glycogen.

branches found in this structure due to the two different ways glucose units can be connected. Each empty circle represents one molecule of glucose.

how is glycogen made

what processes

Glycogen synthesis adds individual glucose molecules to create glycogen.

Glycogen breakdown removes individual glucose units that can then be used for metabolic processes.

aldose numbering

Ch2OH is 6

Glycogen Synthesis

Glycogen synthesis starts with a molecule of glucose 6-phosphate that is converted to glucose 1-phosphate by phosphoglucomutase.

Glucose 1-phosphate is then activated by hydrolysing UTP to generate UDP-Glucose.

New glucose subunits are added to an existing glucose polymer, which is attached to the core, the protein glycogenin.

Glycogen synthase uses a molecule of UDP glucose to add a subunit with a C1-C4 linkage. UDP is released. This extends the glycogen chain by one subunit. This reaction can be repeated until many subunits are added.

Glycogen branches

are formed by branching enzymes which transfer a chain of glucose molecules and create a C1-C6 linkage.

Glycogen Breakdown

Glycogen breakdown requires debranching enzymes to remove the branches attached by a C1-C6 linkage.

Glycogen phosphorylase removes individual glucose units attached to the C1-C4 linkage, generating glucose 1-phosphate, and a chain of glycogen that is one subunit shorter.

The phosphate group of glucose 1-phosphate can be moved to carbon six to generate glucose 6-phosphate.

Summary of Glycogen

key enzymes

In summary, glucose is stored in a branched polymer called glycogen.

Glucose in glycogen is attached by C1-C4 linkages and C1-C6 linkages.

Glycogen synthase is the key enzyme in glycogen synthesis.

Glycogen phosphorylase is the key enzyme in glycogen breakdown.

Branching and debranching enzymes are needed for synthesis and breakdown of the branched glycogen molecule

Glycogen synthesis 1

starts with a molecule of glucose 6-phosphate that is converted to glucose 1-phosphate by phosphoglucomutase.

Glycogen synthesis 2

Glucose 1-phosphate is then activated by hydrolysing UTP to generate UDP-Glucose.

Glycogen synthesis 3

New glucose subunits are added to an existing glucose polymer, which is attached to the core, the protein glycogenin.

Glycogen synthesis 4

what kind of linkage

Glycogen synthase uses a molecule of UDP glucose to add a subunit with a C1-C4 linkage.

UDP is released.

This extends the glycogen chain by one subunit. This reaction can be repeated until many subunits are added.

glycogen breakdown 1

Glycogen breakdown requires debranching enzymes to remove the branches attached by a C1-C6 linkage.

glycogen breakdown 2

Glycogen phosphorylase removes individual glucose units attached to the C1-C4 linkage, generating glucose 1-phosphate, and a chain of glycogen that is one subunit shorter.

glycogen breakdown 3

The phosphate group of glucose 1-phosphate can be moved to carbon six to generate glucose 6-phosphate.