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Pathway

Glycogen metabolism

Homo sapiens · Cytosol · 7 reactions

Glycogen metabolism stores glucose when it is plentiful and mobilizes the branched polymer between meals or during muscle work. Liver glycogen can support blood glucose; muscle glycogen is used locally.

REACTOME IDENTIFIERR-HSA-8982491View source record ↗

Pathway scope

NETWORK MAP

This is a polymer-turnover overview. Polymer chain length and branching change, so no single-molecule net equation is displayed.

Overview

EXPLORE BY LEVEL

Glycogen metabolism is a set of connected chemical steps in human cells. Glycogen metabolism stores when it is plentiful and mobilizes the branched polymer between meals or during muscle work. Liver glycogen can support blood ; muscle glycogen is used locally.

WHY THE FLOW CHANGES

Regulation

Compare fed and fasting

Phosphorylation coordinates glycogen breakdown and storage.

Can speed upInsulin signaling

In liver and muscle it favors glycogen synthase activity and storage after feeding.

Can speed upGlucagon in liver; epinephrine in liver and muscle

These signals favor glycogen breakdown. Muscle contraction also activates muscle glycogen use.

Context mattersOpposing enzyme states

Glycogen synthase and glycogen phosphorylase are coordinated so synthesis and breakdown do not simply run full speed together.

How to read this map

This is an instructional map of selected reactions, not a complete inventory of every reaction in the body. Some steps are grouped; transport, alternate routes, tissue differences, or full molecule balances may be summarized. The Research notes explain this map’s specific limits.

Explore the reaction map and enzyme steps

Pathway map

GENERATED FROM STRUCTURED REACTIONS

Select a molecule or enzyme to inspect it. Select a step number to open its full reaction detail.

  1. Glycogen breakdown

    Phosphorylase releases glucose 1-phosphate; debranching enzyme handles alpha-1,6 branch points.

    1. Step 1Irreversible · Pi → —
    2. Step 2Irreversible · H2O → —

  2. Glucose mobilization

    Glucose 1-phosphate becomes glucose 6-phosphate; only glucose-exporting tissues release free glucose.

    1. Step 3Reversible

  3. Glucose activation

    Glucose 1-phosphate is activated to UDP-glucose for glycogen synthesis.

    1. Step 4Irreversible · UTP → PPi

  4. Chain extension and branching

    Glycogen synthase extends alpha-1,4 chains, and branching enzyme creates alpha-1,6 linkages.

    1. Step 5Irreversible · — → UDP
    2. Step 6Irreversible · — → UDP
    3. Step 7Irreversible

Reaction steps

1Phosphorolysis of glycogenGlycogen → Glucose 1-phosphateIrreversible

Glycogen phosphorylase releases glucose 1-phosphate from non-reducing chain ends.

REACTION · PER TURN + yields
Enzyme
EC 2.4.1.1 ↗
Cofactors
No metal cofactor listed.
Reversibility
Irreversible under cellular conditions. This is a control point.
Runs per glycogen
Once
Stage
Glycogen breakdown
MECHANISM & CONTEXT

Phosphorolysis preserves some of the bond energy in glucose 1-phosphate. Phosphorylase stops near branch points; the debranching enzyme then transfers and hydrolyzes residues.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

2Branch-point removalGlycogen → Glucose 1-phosphate + GlucoseIrreversible

The debranching enzyme rearranges short chains and hydrolyzes alpha-1,6-linked glucose.

REACTION · PER TURN + yields +
Enzyme
EC 3.2.1.33 ↗
Cofactors
No metal cofactor listed.
Reversibility
Irreversible under cellular conditions. This is a control point.
Runs per glycogen
Once
Stage
Glycogen breakdown
MECHANISM & CONTEXT

The enzyme has transferase and alpha-1,6-glucosidase activities. The displayed products summarize its two activities rather than a single balanced reaction.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

3Interconversion with glucose 6-phosphateGlucose 1-phosphate ⇌ Glucose 6-phosphateReversible

Phosphoglucomutase interconverts glucose 1-phosphate and glucose 6-phosphate.

REACTION · PER TURNreversibly yields
Enzyme
EC 5.4.2.2 ↗
Cofactors
No metal cofactor listed.
Reversibility
Reversible, operating near equilibrium in cells.
Runs per glycogen
Once
Stage
Glucose mobilization
MECHANISM & CONTEXT

Liver can dephosphorylate glucose 6-phosphate and export glucose. Skeletal muscle lacks the glucose-6-phosphatase system and retains the carbon for local metabolism.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

4Activation to UDP-glucoseGlucose 1-phosphate → UDP-glucoseIrreversible

UDP-glucose pyrophosphorylase activates glucose 1-phosphate with UTP.

REACTION · PER TURN + yields +
Enzyme
EC 2.7.7.9 ↗
Cofactors
No metal cofactor listed.
Reversibility
Irreversible under cellular conditions. This is a control point.
Runs per glycogen
Once
Stage
Glucose activation
MECHANISM & CONTEXT

Hydrolysis of pyrophosphate helps pull UDP-glucose formation forward.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

5Glycogen-chain initiationUDP-glucose + Glycogen → GlycogenIrreversible

Glycogen synthase transfers glucose from UDP-glucose onto a primer chain.

REACTION · PER TURN + yields +
Enzyme
EC 2.4.1.11 ↗
Cofactors
No metal cofactor listed.
Reversibility
Irreversible under cellular conditions. This is a control point.
Runs per glycogen
Once
Stage
Chain extension and branching
MECHANISM & CONTEXT

Glycogenin provides the protein primer for new glycogen particles; that initiation chemistry is grouped with chain extension in this overview.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

6Alpha-1,4 chain extensionUDP-glucose + Glycogen → GlycogenIrreversible

Glycogen synthase extends existing chains with alpha-1,4-linked glucose residues.

REACTION · PER TURN + yields +
Enzyme
EC 2.4.1.11 ↗
Cofactors
No metal cofactor listed.
Reversibility
Irreversible under cellular conditions. This is a control point.
Runs per glycogen
Once
Stage
Chain extension and branching
MECHANISM & CONTEXT

Glycogen synthase requires a pre-existing primer and does not create branch points.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

7Branch formationGlycogen → GlycogenIrreversible

Branching enzyme creates alpha-1,6 linkages and new non-reducing ends.

REACTION · PER TURNyields
Enzyme
EC 2.4.1.18 ↗
Cofactors
No metal cofactor listed.
Reversibility
Irreversible under cellular conditions. This is a control point.
Runs per glycogen
Once
Stage
Chain extension and branching
MECHANISM & CONTEXT

Branch points increase solubility and provide many ends for rapid synthesis and mobilization. Polymer addition and removal are inherently summarized rather than fully balanced as small-molecule equations.

Evidence for this step: Glycogen metabolism (R-HSA-8982491)

Research sources, claims, and curation

Glycogen metabolism (R-HSA-8982491)

Reactome · Homo sapiens · Reviewed Reactome human pathway used for reaction sequence and context.

Claims

Glycogen metabolism stores glucose when it is plentiful and mobilizes the branched polymer between meals or during muscle work. Liver glycogen can support blood glucose; muscle glycogen is used locally.

Curation notes

  • Glycogen is a polymer; the map uses one generic glycogen entity, so its net stoichiometry is intentionally not calculated.
  • The pathway includes synthesis and breakdown, which are separately regulated and do not normally run in the same direction at once.
  • Reactome's reviewed record combines the synthesis and glycogenolysis modules; tissue-specific physiology is noted in the teaching text.