Lecture 3- Glycogen And Lipid Storage Flashcards
What tissues have an absolute glucose requirement?
Red blood cells
Lens of eye
Neutrophils
Innermost cells of kidney medulla
Stable glucose level absolute requirement for brain function
What is normal blood glucose?
5mmol/L which will increase for a short period after eating.
What is the clinical consequence of having over 8mmol/L glucose over a prolonged period?
Any more glucose that this cannot be absorbed and will be excreted in the urine. Having this elevated level of blood glucose for prolonged periods leads to many of the undesirable effects associated with diabetes
What problems can prolonged elevated plasma glucose cause?
Neuropathy, poor microvasculature and these combined mean that foot damage can be hard to detect and then hard to repair
At what blood glucose level will you suffer brain damage and probable death?
0.6mmol/L
Where in the body is glycogen stored and how is it used?
300g muscle used for energy
100g liver used to maintain plasma glucose levels
How is glycogen structured?
A highly branched polymer with alpha 1-4 bonds and alpha 1-6 bonds which result in branching. Dimer of the protein glycogenin acts as a primer in the centre
Why is glycogen highly branched?
Osmotically inactive in the form and provides lots of points for glucose releasing enzymes to act on
What happens in glycogenesis or glycogen synthesis?
Energy is used to form UDP-glucose which is added to glycogen molecule through either glycogen synthase which makes the alpha 1-4 glycosidic bonds or branching enzyme which makes the alpha 1-6 glycosidic bonds
What happens in glycogenolysis
Glycogen is acted on by glycogen phosphorylase and de-branching enzyme to ultimately make glucose 6 phosphate to be used by muscle or glucose to be released into blood by the liver
Are glycogenolysis and glycogenesis the revers of each other?
No, they use different enzymes which allows for simultaneous inhibition of one pathway and stimulation of the other.
If enzymes weren’t different both pathways would have to run at the same time.
What enzymes are primarily responsible for glycogen synthesis and breakdown?
Glycogen synthase and glycogen phosphorylase
Effect of glucagon and adrenaline on glycogen?
Cause the phosphorylation of glycogen synthase which inhibits it and the phosphorylation of glycogen phosphorylase which activates it.
Effect of insulin on glycogen synthesis?
De phosphorylase glycogen synthase which activates it and de phosphorylase glycogen phosphorylase which deactivates it
What acts as an allosteric activator for muscle glycogen phosphorylase but not the liver enzyme?
AMP (low energy need breakdown of glycogen)
Effect of glucagon on muscle glycogen stores?
Has no effect
Glycogen storage disease examples?
Von Gierke’s disease- glucose 6 phosphate deficiency results in liver glycogen not being mobilised and enlargement of the liver can result
McArdle’s disease-
Muscle glycogen phosphorylase deficiency which results in tired muscles as cant mobilise glycogen
What happens in gluconeogenesis?
Beyond 8 hours of fasting it kicks in. It uses glycerol, lactate and amino acids to make glucose and it occurs in the liver and kidney to a small degree
Can acetyl Co-A be used in gluconeogenesis?
No as the reaction that created acetyl Co-A using the enzyme pyruvate dehydrogenase is irreversible
Gluconeogenesis enzymes?
Some different to glycolysis. Phosphoenolpyruvate carboxykinas (PEPCK), fructose 1,6-bisphosphatase and glucose-6-phosphatase are the key enzymes
Insulin inhibits while cortisol and glucagon stimulate
What are the two key regulatory enzymes of glycolysis?
Phosphoenolpyruvate carboxykinas (PEPCK) and fructose 1,6-bisphosphatase which are activated and inhibited by glucagon/ cortisol and insulin respectively
Time course of glucose utilisation?
Glucose from food up to 2 hours
Glycogenolysis for next 8-10 hours
Gluconeogenesis another 10 hours
What is triacylglycerol?
Three fatty acids and a glycerol
Why are triacylglycerols stored in adipose tissue?
Because they are hydrophobic