Biochemistry- gluconeogenesis Flashcards
What is gluconeogenesis?
The synthesis of glucose within the body from non-carbohydrate precursors
When is gluconeogenesis required?
During prolonged starvation
What are the precursors for gluconeogenesis, and where are they derived from?
Lactate- synthesised by skeletal muscles under anaerobic conditions.
amino acids- derived from muscle protein by proteolysis
glycerol- derived from triglycerides by lipolysis in adipose tissue
Why does gluconeogenesis require energy?
Because it is making something big out of something small
Where does the energy required for gluconeogenesis come from?
From oxidation of stored molecules. This is initially from fatty acids stored in adipose tissue but can also be derived from breakdown of body protein.
Where does gluconeogenesis occur?
Mainly in the liver
Small amounts in the kidneys
Why enzymes catalyse the irreversible reactions in glycolysis?
Why is gluconeogenesis not just reverse of glycolysis?
Hexokinase
phosphofructokinase
pyruvate kinase
Gluconeogenesis is not just reverse of glycolysis because there are these irreversbile reactions (1,3, and last in glycolysis) which must be bypassed.
What intermediate is produced in gluconeogenesis, which is in the mitochondria, and is important in accepting acetyl groups from fat breakdown?
Oxaloacetate
How many ATP molecules are required for each glucose generated?
6
What is the cori cycle?
The cycle in which lactate is formed, then used as a percursor for gluconeogenesis.
Firstly, lactase is formed in fast-twitch muscle fibres under conditions of heavy exercise.
Blood transports the lactate to the liver (lactate is polar so can travel to the liver in the blood).
The liver converts lactate back to glucose
Glucose is released into the bloodstream
This buys time and shifts the metabolic burden of muscle to other organs.
Why can the cori cycle not go on forever?
Because it generates less ATP than it consumes.
What are the two types of amino acids, in the context of gluconeogenesis?
Ketogenic amino acids- those which cannot act as precursors for gluconeogenesis
Glucogenic amino acids- those which can acts as precursors for gluconeogenesis.
How do glucogenic amino acids enter the TCA cycle?
They either enter the TCA cycle as amino acids at various stages, or they are converted to pyruvate and then enter the TCA cycle that way.
Why can the TCA cycle only proceed if oxaloacetate is present?
Because one oxaloacetate goes into the TCA cycle to accept an acetyl group, and one comes out at the other end.
How can ketogenic amino acids enter the TCA cycle?
They can be converted to acetoacetyl coA, and then converted to acetyl coA and enter the TCA cycle that way, but only if oxaloacetate is already present, because it is required to accept the acetyl coA.
