Brenda - Gluconeogenesis Flashcards
What does gluconeogenesis mean?
Biosynthesis of new glucose
List the five primary carbon skeletons used for gluconeogenesis
Pyruvate
Lactate
Glycerol
Alanine
Glutamine
List the three places gluconeogenesis occurs
Mainly in the liver
Kidney
Small intestine
What are the three irreversible reactions in glycolysis?
Hexokinase
Phosphofructokinase
Pyruvate kinase
What is done to the three irreversible reactions in glycolysis during gluconeogenesis?
These 3 irreversible reactions are bypassed in gluconeogenesis
How does GNG overcome the irreversible pyruvate kinase reaction
(6)
There is two parts:
Pyruvate is converted into 2 oxaloacetate
This is catalysed by pyruvate carboxylase
This reaction needs ATP (dephosphorylation of ATP occurs)
This reaction needs biotin
Occurs in mitochondrial matrix
Oxaloacetate moves into the cytosol where it is reoxidised into 2 phosphoenolpyruvate
What is the first step, part b of GNG, oxaloacetate has been generated?
Oxaloacetate moves into the cytosol where it is reoxidised into 2 phosphoenolpyruvate
What must oxaloacetate be converted into in order to leave the mitochondria?
(2)
Oxaloacetate is converted into malate (reduction)
It is then converted back into oxaloacetate
How does GNG overcome the second irreversible reaction (phosphofructokinase)
Fructose-1,6-bisphosphate is converted into fructose-6-phosphate
Catalysed by fructose-1,6-bisphosphatase
How does GNG overcome the third irreversible reaction (hexokinase)
(2)
Glucose-6-phosphate is converted into glucose
Catalysed by glucose-6-phosphatase
What happens to some of the lactate produced in muscle?
(2)
Some enters the liver where it is reoxidised to pyruvate where it can then undergo gluconeogenesis
Cori cycle
How do plants and bacteria convert their fatty acids to carbohydrates?
Acetyl-CoA is incorporated into carbohydrates via the glyoxylate cycle
How do plants and bacteria convert their fatty acids to carbohydrates?
Acetyl-CoA is incorporated into carbohydrates via the glyoxylate cycle
What is animals’ only fat breakdown product for gluconeogenesis?
Glycerol
What type of diet can lower gluconeogenesis?
A high carbohydrate diet
What type of diet can increase gluconeogenesis?
Fasting or low carbohydrate diet
What can strongly inhibit gluconeogenesis and cause hypoglycaemia?
Ethanol strongly inhibits gluconeogenesis
In general how do mechanisms inhibit gluconeogenesis?
They cause oxaloacetate to be reduced to malate which makes it unavailable for GN
What is the blood glucose resting level?
4-5mM
What is blood glucose level after a meal?
8-9mM
What happens when blood glucose is high?
(2)
Pancreas reduces glucagon secretion
Pancreas increases insulin secretion
What do liver cells do when there is high blood glucose?
Glucose enters liver cells and is stored as glycogen or used for TAG synthesis
How does the liver sustain blood glucose levels when fasting?
By degrading glycogen stores
How does the pancreas respond to lower glucose levels?
As glucose decreases, insulin secretion is reduced and glucose is taken up by muscle and adipose tissue
Glucagon secretion is increased which accelerates glycogenolysis
How does the body react to starvation?
(2)
Fatty acids are mobilised from adipose tissue and oxidised by muscle
In the liver any accumulated acetylCoA is converted to ketone bodies
How does the liver keep glucose levels up during starvation?
(2)
By using gluconeogenesis substrates to maintain glucose levels
And by forming ketone bodies
What two organs have substantial capacity to oxidise ketone bodies?
Brain
Cardiac muscle
Why does the need to use some glucose even in starvation?
To maintain ion gradients for transmission of nerve impulses and for the synthesis of neurotransmitters
What affects does hypoglycaemia have on the brain?
ATP production in the brain cells falls
Impairs brain cells electrical activity
Causes a coma
