Metabolic pathways: gluconeogenesis Flashcards
When does gluconeogenesis occur?
During prolonged starvation
What is gluconeogenesis?
Synthesis of glucose
What are the precursors of gluconeogenesis?
Lactate- synthesised by skeletal muscle
Amino acids- derived from muscle protein by proteolysis
Glycerol- derived from triglycerides by lipolysis in adipose tissue
Where does energy come from?
Oxidation of fatty acids released from adipose tissue
Where does gluconeogenesis occur?
Liver, small amount in the kidney
What are the three irreversible reactions in glycolysis?
the 1st, 3rd last reaction
Catalysed by
Hexokinase
Phosphofructokinase
Pyruvate kinase
What is requires for gluconeogenesis?
Additional enzymes to bypass irreversible stages
How many enzymes are required to bypass irreversible reactions?
4 liver enzymes
What does glucogenogenesis proceed via?
The synthesis of oxaloacetate in mitochondria
- the TCA cycle intermediate which accepts acetyl groups
- important for accepting acetyl groups for fat breakdown
How many pyruvate are needed to make a glucose molecule?
2
What is important about glugoneogenesis ?
Very energy expensive
- 4ATP
- 2GTP are consumed to make one glucose
Where does lactate come from?
Formed in fast-twitch muscle under conditions of heavy exercise
Blood transports lactate to liver
Converted back to pyruvate
Costs 6ATP to form glucose
What is the significance of lactate as a precursor?
Allows muscle to continue for at least a while
What are the two groups of amino acids?
Keto-genic = cannot be used for making glucose
Glucogenic= can be used for making glucose
What happens if gluconeogenesis removes oxaloacetate?
The TCA cycle cannot acept further acetyl groups