Introduction to Glycogen Flashcards
What is glycogen?
- Storage form of glucose.
- Found in bacteria, archaea and eukaryotes.
Describe glycogen branching
- Increased number of terminal sugar residues for attack during rapid glycogenolysis.
- Branching increases solubility of glycogen.
- Occurs around a protein called glycogenin.
What bonds are present in glycogen
- Branched polymer of glucose.
- Individual inear chains have a-1,4-glycosidic bonds.
- Branch points have a-1,6-glycosidic bonds.
TRUE or FALSE: Glycogen is found as granules (10-40 nm diameter) in the cytoplasm of liver and skeletal muscle cells.
TRUE
What is Glycogenolysis?
The breakdown of glycogen
What are the 3 steps of Glycogenolysis?
- Release of glucose 1-phosphate from glycogen.
- Remodelling of glycogen substrate to permit further degradation.
- Conversion of glucose 1-phosphate to glucose 6-phosphate for further metabolism.
Describe Glycogenlysis step 1
•Glycogen phosphorylase cleaves glycogen by addition of orthophosphate (Pi).
Describe Glycogenlysis step 2
Debranching enzyme is required as phosphorylase only attacks the a-1,4 linkages.
- Transfer of 3 glucosyl residues from an a-1,6 linkage to an a-1,4 linkage (4-a-D-glucanotransferase activity)
- Removal of the a-1,6-linked glucosyl by a-1,6-glucosidase.
Describe glycogenlysis step 3
Phosphoglucomutase converts glucose 1-phosphate to glucose 6-phosphate.
Glucose-1-phosphate enters the active site there is a phosphorylated serine
The phosphate is transferred onto the glucose (position 6)
The position 1 phsophate is removed and put back onto the serine
Why can’t glucose be stored at high concetrations?
- Osmotic gradient of glucose
- Glucose tends to be transported by passive transport mechanisms so you can never get as high a concentration inside the cells as outside
