Lecture 3- Energy storage (glycogen) Flashcards
which tissues have an absolute requirment for glucose as an energy source
- RBC
- Neutrophils- resp burst
- Innermost cells of kidney medulla- blood supply low because so deep
- Lens of the eye- not very rich blood supply (oxidative phos limited)
brain’s energy source
- Stable BG essential for normal brain function
- Brain has a requirement for glucose
- Can use ketones but takes a while to adapt
normal BG
5mmol
To enable bg to be kept at stable levels glucose is stored as
glycogen
consequence of hypoglycaemia (2.8 mmol/L)
confusion
consequence of hypoglycaemia (1.7 mmol/l)
weakness and nausea
consequence of hypoglycaemia (1.1 mmol/l)
muscle cramps
consequence of hypoglycaemia (0.6 mmol/l)
brain damage and death
glycogen is stored as ……….. in the ….. and ……
- Glycogen is stored as granules
- Muscle
- Liver
glycogen in muscle
Distinction between intra and intermyofibrillar glycogen
Glycogen in muscle= for muscle contraction
how is glycogen stored in the liver
Glycogen stored as granules in hepatocytes
Glycogen store in liver= buffers plasma glucose levels
examples of conditions which cause hypoglycaemia
- e.g. diabetic patient which has taken insulin injections and forgotten to eat meal
- e.g. Someone with acute alcoholic poisoning
- e.g. Athlete which has pushed themselves over the limit
see the effects of hypoglycaemia if the bg drops to
2.8 mmol/l
structure of glucogen
- Glycogen is a polymer consisting of chains of glucose residues
- Chains are organised like the branches of a tree originating from a dimer of the protein glycogenin (acts as a primer at core of glycogen structure)
- Glucose residues linked by alpha1-4 glyosidic bonds with alpha 1-6 glyosidic bonds forming branch points every 8-10 residues
protein glycogenin
(acts as a primer at core of glycogen structure)
why does glycogen have this structure
- Will release glucose quickly
- Reduces the osmotic effect on the cell
glycogenesis is the pathway by which
glycogen is synthesised
glycogenolysis is the pathway by which
glycogen is degraded to produce glucose or be used in glycolysis
synthesis of glycogen requires
Energy (ATP)
outline glycogenesis
- glucose is convert to glucose 6-phosphate by hexokinase
- glucose 6-phosphate is converted to glucose 1-phosphate by phosphoglucomutase
- glucose 1 phohate is converted to UDP glucose by G1P uridylyltransferase
- glycogen (n residues) + UDP-glucose –> glucogen (n +1 + UDP
- glycogen synthase–> alpha 1-4 glycosidic bonds
- branching enzyme –> alpha 1-6 glycosidic bonds
outline glycogenolysis
- glycogen (n residues) + Pi –> Glycose 1-phosphate _ glycogen (n-1 residues)
- glycogen phosphorylates or de-branching enzyme
- glucose 1-phosphate –> glucose 6-phopshate
- in the muscle glucise 6-phosphate is used by muscle for energy production
- in the liver glucose-6 phophate is converted to glucose and rleeased into the blood
function of glycogen storesin the liver
- G6P converted to glucose and exported to the blood
- Acts as a buffer of blood glucose levels
Function of glycogen stores in the muscle
- Muscle lacks the enzyme glucose-6-phosphatase
- G6P enters glycolysis for energy production
summary of glycogenolysis and glycogenesis
lactate from
anaerobic glycolysis in exercising muscle and red blood cells (cori cycle)
Key enzymes of glucoseneogenesis
1) Phosphoenolpyruvate carboxykinase (PEPCK)
2) Fructose 1,6-bisphosphatase
3) Glucose-6- phosphatase
in response to starvation which hormones are released and what is effect on glucoseneogenesis enzymes
glucagon and cortisol are released
- PEPCK - increased amount
- fructose 1,6 bisphosphatase - icnreased amount snad activitity
effect- stimulates glyconeogensis
