The document summarizes the process of glycogenesis, or the synthesis of glycogen from glucose. It involves multiple enzymatic steps: (1) glucose is converted to glucose-6-phosphate then glucose-1-phosphate, (2) UDP-glucose is synthesized from glucose-1-phosphate and UTP, (3) a small fragment of existing glycogen acts as a primer, with the initial glucose attached to glycogenin by glycogen initiator synthase, (4) glycogen synthase elongates the primer by adding glucose units with alpha-1,4 linkages, while glucosyl-4,6 transferase introduces alpha-1,6 branch linkages, building the glycogen molecule.

1. PRASHANT KUMAR KATIYAR
Mail Id: pkatiyar1981@gmail.com

2.  The synthesis of glycogen from glucose is
called as glycogenesis.
 Glycogenesis takes place in the cytosol &
requires ATP and UTP(Uridine triphophate),
besides glucose.
 Steps:
 Synthesis of UDP-glucose:

3. Glucose
Glucose-6P
ADP
ATP
Glucokinase
Glucose-1P
Phosphoglucomutase
UDP-Glucose
UDP
UDP glucose
pyrophosphorylase
PPi
UTP

4. UDP-Glucose
UDP
Glycogen initiator
synthase
OH
UDP
O
Glycogen Primer
Glycogenin
13UDP
13UDP
Glycogen synthase
O
10 161
Primer- Initiate Glycogen Synthesis
-OH Group of AA Tyrosine
Of Glycogenin is the site
at which the initial glucose
Is attached.
First molecule of Glucose to
Glycogenin

5. O
Glucosyl transferase
10 161
O
101
16
7
11
Elongation by glycogen
synthase (ɑ1,4 bonds
Branching by glucosyl 4,6
transferase (ɑ1,6 bonds)
Glycogen

6.  Synthesis of UDP-glucose:
 The enzymes hexokinase (in muscle) &
glucokinase (in liver) convert glucose to
glucose 6-phosphate
 Phosphoglucomutase catalyses the
conversion of glucose 6-phosphate to glucose
1-phosphate.
 Uridine diphosphate glucose (UDP-glucose) is
synthesized from glucose 1-phosphate & UTP
by UDP-glucose pyrophosphorylase.

7.  A small fragment of pre-existing glycogen
must act as a ‘primer’ to initiate glycogen
synthesis.
 A specific protein ‘glycogenin’ can accept
glucose from UDP Glucose.
 The hydroxyl group (OH) of the amino acid
tyrosine of glycogenin is the site at which the
initial glucose unit is attached.

8.  The enzyme glycogen initiator synthase
transfers the first molecule of glucose to
glycogenin.
 Then glycogenin itself takes up a few
glucose residues to form a fragment of
primer which serves as an acceptor for the
rest of the glucose molecules.

9.  Glycogen synthase is responsible for the
formation of 1,4-glycosidic linkages.
 This enzyme transfers the glucose from UDP-
glucose to the non-reducing end of glycogen to
form ɑ- 1,4 linkages.

10.  Glycogen synthase can catalyse the synthesis
of a linear unbranched molecule with -ɑ 1,4
glycosidic linkages.
 Glycogen is a branched tree-like structure.
 The formation of branches is brought about by
the action of a branching enzyme, namely
glucosyl -4-6 transferase.

11.  This enzyme transfers a small fragment of 5 to
8 glucose residues from the non-reducing end
of glycogen chain (by breaking -ɑ 1,4 linkages)
to another glucose residue where it is linked
by -ɑ 1,6 bond.
 This leads to the formation of a new non-
reducing end, besides the existing one.
 Glycogen is further elongated & branched, by
the enzymes glycogen synthase & glucosyl 4-6
transferase.

12. Glucose
Glucose-6P
ADP
ATP
Glucokinase
Glucose-1P
Phosphoglucomutase
UDP-Glucose
UDP
UDP glucose
pyrophosphorylase
PPi
UTP

13. UDP-Glucose
UDP
Glycogen initiator
synthase
OH
UDP
O
Glycogen Primer
Glycogenin
13UDP
13UDP
Glycogen synthase
O
10 161
Primer- Initiate Glycogen Synthesis
-OH Group of AA Tyrosine
Of Glycogenin is the site
at which the initial glucose
Is attached.
First molecule of Glucose to
Glycogenin

14. O
Glucosyl transferase
10 161
O
101
16
7
11
Elongation by glycogen
synthase (ɑ1,4 bonds
Branching by glucosyl 4,6
transferase (ɑ1,6 bonds)
Glycogen

15. Glycogen

16.  Textbook of Biochemistry – U
Satyanarayana
 Textbook of Biochemistry – DM Vasudevan