GLYCOGENESIS

What is the starting point molecule of glycogenesis

glycogenin

300 amino acids self glycosylating

what are the 2 isoforms of glycogenin

Glycogenin 1 and Glycogenin 2

Where are the 2 isoforms expressed

1: skeletal and cardiac muscle

2: liver

What does the surface of glycogenin promote

glycogen alpha particle formation

Describe the activation of G-1-P for glycogenesis by UTP

Uridine triphosphate (UTP) combines with G-1-P.

2 phosphates are lost - pyrophosphate

We get uridine-diphosphate-glucose

What is the key enzyme is glycogenesis

Glycogen synthase

What are the 2 isoforms of glycogen synthase inhibited by

phosphorylation of various Ser residues by AMP kinase, PKA, casein kinase 2 and glycogen synthase kinase 3

Where are the 2 isoforms expressed

1: muscle

2: liver

STEP 1

transporter proteins bring glucose into the cell

glucose is acted on by hexokinase:

Glucose + ATP → G-6-P + ADP

STEP 2

Phosphoglucomutase shifts phosphate from sixth to first carbon → G-1-P

STEP 3

UDP-glucose pyrophosphorylase combines Uridine triphosphate (UTP) with G-1-P.

2 phosphates are lost - pyrophosphate

We get uridine-diphosphate-glucose

STEP 4

Glycogen synthase adds glucose to the non-reducing end of a glycogen chain - forming a-1,4 glycocidic bonds

If no glycogen is present glycogenin acts as a primer and an enzyme autoglycosylating itself with glucose residues from UDP-glucose to start the chain

STEP 5

Branching enzyme creates an internal alpha-1,6 linkage

7 glucose units transferred from at least 11 glucose units and adding to at least 4 glucose units distal to another branch poin

Protein phosphatase 1 in regulation of glycogen (it wants glycogen)

It dephosphorylates

- this activates glycogen synthase: promoting glycogenesis

- inactivates glycogen phosphorylase and phosphorylase kinase: inhibiting glycogen breakdown

How many glycogen storage diseases are there - what are the main ones

15

Vice (Von Gierke Disease)

President (Pompe Disease)

Can’t (Cori Disease)

Accept (Andersen’s Disease)

Money (McArdle’s Disease)

Cori disease

Glycogen debranching enzyme deficiency. will effect liver

Anderson’s disease

branching enzyme deficiency

Vin Gierke disease

G-6-P deficiency