Glycogen synthesis

Parent
Glycogen metabolism glucan biosynthesis
Gene Ontology
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The glycogen synthesis is the construction of the storage form of glucose ( dextrose ), the glycogen . This consists of long, branched chains made up of individual glucose molecules. The process takes place in most living things.

So that individual glucose molecules can be linked, they must first be converted into UDP-glucose by phosphorylation and thus activated. This link creates a branched molecule. This structure has the advantage that glycogen, for example in muscles, can be broken down at many ends at the same time during rapid contraction to provide energy.

The reverse process is glycogenolysis .

The synthesis of glycogen from glucose

Construction steps

Glycogen synthesis is made up of different steps:

Hexokinase reaction

In the first step the glucose is converted into glucose-6-phosphate . This purpose is served glucokinase ( hexokinase IV ), also in the glycolysis phosphorylated glucose; the reaction consumes one ATP molecule per glucose unit as an energy and phosphate supplier. An ADP molecule is produced as a by-product:

+ ATP + ADP ${\displaystyle \mathrm {\xrightarrow {Hexokinase}} }$

Phosphoglucomutase reaction

Glucose-6-phosphate is isomerized to glucose-1-phosphate by phosphoglucomutase , the equilibrium reaction being shifted to the right side due to the constant removal of glucose-1-phosphate by the next reaction. Glucose-1,6-bisphosphate is formed as an intermediate product of the reaction :

${\displaystyle \mathrm {\xrightarrow {Phosphoglucomutase}} }$

Glucose-1-phosphate UTP transferase reaction

The actual activation of glucose-1-phosphate takes place through reaction with uridine triphosphate ( UTP ). A part of the UTP is linked to the phosphate group of the glucose, while the two outer phosphate residues ( beta and gamma phosphate ) of the UTP are split off. The activated UDP-glucose is produced .

+   ${\displaystyle {\xrightarrow[{-2Phosphat}]{Kat}}}$ 

The reaction is catalyzed by glucose-1-phosphate UDP transferase .

Glycogen synthase reaction

Glycogenin center with attached glycogen molecules

UDP-glucose is used for the actual glycogen synthesis, whereby the UDP-glucose is transferred to an existing glycogen molecule by the glycogen synthase and uridine diphosphate ( UDP ) is split off. For the initial synthesis of glycogen, a starter molecule, a so-called core protein , is required, which is provided by the glycogenin . This forms the center of every glycogen molecule. It itself has a few molecules of α-1,4-glycosidically bound glucose, which are required by glycogen synthase as a primer - this enzyme slides along the existing chain of glucose molecules like a slide on a zipper and cannot itself determine a starting point . This reaction creates a chain of unbranched glycogen.

Branching enzyme

The 1,4-α-glucan-branching enzyme or branching enzyme is used to create branches in the linear chain: it cuts the strand every 7 to 12 glucose units and adds the cut piece of alpha-1,6-glycosidic branching to the side to a chain at least 11 molecules long.

literature

• G. Löffler, PE Petrides, PC Heinrich: Biochemistry & Pathobiochemistry. 8th edition, Springer, Heidelberg 2006, ISBN 978-3-540-32680-9 , pp. 368-370

Individual evidence

1. ↑ UniProt search result: GO: 0005978 for taxon
2. ↑ reactome: Glycogen synthesis  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.  

Web links

Wikibooks: Biochemistry and Pathobiochemistry: Glycogen Synthesis  - Learning and Teaching Materials

• reactome: glycogen synthesis