Biochemistry Podcast - Glycogen Flashcards
what is glycogenesis?
The synthesis of glycogen from glucose
What is glycogenolysis?
The breakdown of glycogen to form glucose
What is glycogen?
The main storage form of glucose in liver and muscle cells
Describe liver glycogen?
It can be broken down in between meals to maintain the blood glucose levels and provide glucose for red blood cells and the brain
Describe muscle glycogen?
It is not available to be broken down for maintenance of blood glucose levels.
It can be used only in muscle cells, and can provide energy via glycolysis and the TCA during bursts of physical activity.
How does muscle use glycogen to provide energy during physical activity?
It can provide energy via glycolysis and the TCA cycle during physical activity
Describe how blood sugar levels are kept fairly constant between meals?
Dietary carbs provide 100% sours of blood sugar however is rapidly depleted from the blood stream after a meal
The liver then provides a source of blood sugar between the meals via GLYCOGENOLYSIS
At night when the glycogen stores are depleted GLUCONEOGENSIS takes place which is when the liver makes new glucose from non carb products
What is the structure of glycogen
glycogen is a polymer.
Single glucose molecules linked together by alpha 1-4 glycosidic links
Glycogen is branched, branches introduced every so often, formed by alpha 1-6, glycosidic links
what is at the centre of glycogen
Glycogenic protein - has catalytic activity, can add small numbers of glucose molecules to itself (up to 4)
What enzyme synthesis glycogen?
Glycogen synthase - can only add glucose to existing glycogen, thus it is important that something acts as a primer
What does glycogen synthesis start with?
The phosphorylation of glucose to glucose-6-phosphate
Roughly describe glycogen synthesis?
Glucose must be phosphorylated to glucose-6-phosphate, it must then be made into glucose-1-phosphate, the glucose-1-phosphate is activated to UDP glucose (using UTP), this UDP glucose can then be added onto an existing glycogen chain using glycogen synthase (leaving behind a UDP)
How many ATPs does glycogen synthesis require?
1 ATP per molecule of glucose added
What is UDP glucose?
A uridine diphosphate with a glucose molecule attached to it.
It is a nucleotide
What is the activated form of glucose?
UDP glucose
What does the phosphate ester linkage in a nucleotide sugar release?
Free energy on hydrolysis
Can glycogen synthase introduce branches?
NO
What is the rate limiting enzyme of glycogenesis?
Glycogen synthase
What enzyme is able to introduce alpha 1-6,glycosidic branches into glycogen?
Transglycosylase
Adds a branch approx every 10 glucose residues
What is the product of glycogenolysis?
Glucose-1-phosphate
What catalyses glycogenolysis?
Glycogen phosphorylase
What then happens to the glucose-1-phosphate in glycogenolysis?
It is converted into glucose-6-phosphate
What happens to glucose-6-phosphate in the liver in glycogenolysis?
It can be de-phosphorlyated and the resulting glucose is released into the bloodstream
What happens to glucose-6-phosphate in the skeletal muscle in glycogenolysis?
IT CANNOT de-phosphorylate it but it can use it to provide energy via glycolysis and the TCA cycle - can only feed that muscle cell
Is the only enzyme needed to breakdown glycogen glycogen phosphorylase?
No you need an enzyme to breakdown the branches in the glycogen chains
What is the rate limiting step in glycogen breakdown?
Glycogen phosphorylase turning glycogen into glucose-1-phosphate
What catalyses the conversion of glucose-6-phosphate into glucose?
Glucose-6-phosphatase
HAPPENS ONLY IN THE LIVER
Via what transporter does glucose made from glucose-6-phosphate enter the blood?
GLUT2 transporter
HAPPENS ONLY IN THE LIVER
When does regulation of the pathways glycogenolysis and glycogenesis occur?
Glycogen synthase
Glycogen phosphorylase
What does insulin do?
Insulin - in the fed state, stimulates synthesis of glycogen, stimulates glycogen synthase and inhibits glycogen phosphorylase
What does glucagon do?
-starving state, lack of glucose in blood stream
Stimulate glycogen phosphorylase, stimulate breakdown og glycogen
Inhibit glycogen synthase
What does adrenaline and cortisol do?
They stimulate glycogen phosphorylase - these hormones stimulate a need for energy
What are the group of diseases in which there are problems with increased glycogen deposits in liver or muscle or both?
Glycogen storage diseases - defects in different enzymes related to glycogen synthesis and breakdown
