Glycogen -gluconeogenesis Flashcards
Differentiate glycogenesis from glycogenolysis
glycogenesis- Synthesis of glycogen from glucose
Glycogenolysis- breakdown of glycogen to form glucose
When is liver glycogen broken down?
Broken down between meals and released to maintain blood glucose levels for red blood cells and brain
When is muscle glycogen used?
Not available for maintenance of blood glucose levels
Provides energy during bursts of physical activity
What is required when hepatic glycogen is depleted?
Gluconeogensis is th eprimary source of glucose overnight
Where can glucose residues be added to?
Only be added to an exisitng glycogen chain
UDP-glucose acts an an intermediate what is required on this intermediate?
Requires a glycogen ‘primer’ containing at least 4 glucose residues. The primer is covalently attached to a protein called glycogenin
What can UDP-glucose be thought as?
An ‘activated’ form of glucose
What catalyses the reaction of the formation of UDP-glucose?
Is the reaction reversible?
UDP-glucose pyrophosphorylase
Yes
What does glycogen synthase do?
Synthesises glycogen from UDP-glucose- the rate limiting enzyme of glycogenesis
Adds one glucose molecule to glycogen at a time
What can glycogen synthase not do?
They can only extend the chains of glycogen meaning they cannot introduce branches or start new molecules
Approx every 10 glucose residues what happens to the branching enzyme?
A transglycosylase, introduces alpha 1-6 glycosidic branches into glycogen
In glycogenesis: After a hyperglyceamia stimuli occurs what is the hormone and effect that is activated after the high levels of glucose?
Hormone- Insulin (pancreatic beta cells)
Effect- Activation of insulin receptors
In glycogenesis: After hypoglycaemia stimuli occurs what is the hormone and effect that is activated after the low levels of glucose?
Hormone- Glucagon (pancreatic alpha cells)
Effect- Inactivation
What is glycogenolysis catalysed by?
Glycogen phosphorylase
In glycogenolysis what are the three steps that occur?
- Rate limiting step
- One glucose molecule is cleaved of the ends of glycogen at a time
- glucose-1-phosphate is then converted to glucose-6-phosphate
In glycogenolysis what happens in the liver?
Glucose 6-phosphate can be de-phosphorylated and the resulting glucose released into the blood stream
In glycogenolysis what happens in (skeletal) muscle?
In glucose 6-phosphate cannot be de-phosphorylated but instead is used to provide energy via glycolysis and the TCA cycle
In glycogenolysis: After hyperglycaemia stimuli occurs what is the hormone and effect that is activated after the high levels of glucose?
Hormone- Insulin (pancreatic Beta cells)
Effect- Inactivation
In glycogenolysis: After stress stimuli occurs what si the hormone and effect that is actiavted after?
Hormone- Corisol (adrenal cortex)
Effect- Activation
In glycogenolysis: After stress and hyperglycaemia what is the hormone and effect activated after/
Hormone- Adrenaline (adrenal medulla)
Effect- Activation
In glycogenolysis: After hyperglycaemia what is the hormone and effect that is activated after?
Hormone- Glucagon (pancreatic alpha cells)
Effect- Activation
What happens after prolonged starvation in gluconeogenesis?
New glucose has to be synthesised
What is gluconeogenesis?
Synthesis of glucose within the body from non-carbohydrate precursors
Essentially the reverse of glycolysis
What are the precursors involved in gluconeogenesis?
Lactate- Synthesised by skeletal muscle under anaerobic conditions
Amino acids- derived from muscle protein by proteolysis
Glycerol- Derived from triglycerides by lipolysis in adipose tissue
Where does the energy come from in glyconeogenesis and where is it released from?
From oxidation of fatty acids released from adipose tissue
Where does gluconeogenesis occur?
Mainly in the liver, small amounts in the kidneys
How many essentially reversible reactions occur in glycolysis?
- Hexokinase
- Phosphofructokinase
- Pyruvate kinase
What are the four unique liver enzymes required in gluconeogenesis?
- Glucose-6-phosphatase
- Fructose-1,6-biphosphatase
- PEP carboxykinase
How does the gluconeogenesis proceed via the synthesis of oxaloacetate in mitochondria?
the C4 TCA cycle intermediate which accepts acetyl groups
‘anaplerotic reaction’
What is the anaplerotic reaction important for?
Important for accepting acetyl groups from fat breakdown
Is gluconeogenesis energetically expensive?
Yes
What is the cori cycle formed by?
three different organs
Liver, blood and muscle
Describe the role of the different components in the cori cycle?
Blood transports lactate to the liver
Liver converts lactate back to glucose
glucose is released into the blood stream
Buys time and shifts metabolic burden from the muscle to other organs
