Gluconeogensis Flashcards
when does Gluconeogenesis occur
- occurs in the liver under starvation
- occurs in periods of intense anaerobic exercise
what is Gluconeogenesis
this is making glucose
what are the substrates that can be used in glucokneosis
- Using carbon part of amino acids from proteins
- From lactate in the blood coming from glycolysis in the muscle tissue from anaerobic respiration
- From glycerol
what cannot undergo glucogenogensis
Can’t be done from fatty acids as they produce acetyl CoA which can’t be used to make glucose, but can provide energy for the reaction.
what are the 3 steps that have to be reversed in glycolysis in order for gluconeogensis to happen
- glucose being converted to glucose-6-phosphate via glucokinase (only in the liver)
- o Fructose-6-phosphate converted to fructose-1,6-bisphophate using phosphofructokinase
- phosphoenolpyruvate to pyruvate via pyruvate kinase
how does the liver overcome the 3 unidirectional steps
o Glucokinase can be overcome using glucose-6-phosphatase, therefore glucose-6-phosphate can be converted back to glucose
o Phosphofructokinase is overcome by fructose-1,6-bisphosphatase, therefore fructose-1,6-bisphophate is converted back to fructose-6-phosphate
o Pyruvate kinase is overcome by pyruvate carboxylase (PC), malate dehydrogenase (MDH) and phosphoenolpyruvate carboxykinase (PEPCK) this causes pyruvate to be converted back to phosphoenolpyruvate
describe how pyruvate is converted back to PEP (phosphoenolpyruvate)
o Pyruvate passes into mitochondria and then converted to oxaloacetate by pyruvate carboxylase
- pyruvate is converted form a 3 carbon molecule to a 4 carbon molecule
- energy is required for this reaction it converts ATP to ADP
o No transporter for oxaloacetate so converted to malate to pass out of the mitochondria this is catalysed by MDH
o Malate then converted back to oxaloacetate in the cytosol this is catalysed by MDH again
o PEPCK converts oxaloacetate phosphoenolpyruvate
- 4 carbon compound converted to a 3 carbon compound this produces carbon dioxide and GTP is converted to GDP as this requires energy
o Called a malate shuttle as malate used to get between the mitochondria matrix and cytosol
- phosphoenolpyruvate can then go up the glycolysis route from pyruvate to glucose and makes glucose
describe fatty acid metabolism
- fatty acids are broken down to acetyl CoA and NADH by beta oxidation
- acetyl CoA cannot be converted to glucose
- Acetyl CoA activates pyruvate carboxylase and this inhibits pyruvate dehydrogenase
- This means that any compound that can produce pyruvate will not form acetyl CoA and instead be used to glucose formation using the energy from fatty acid oxidation
- energy for fatty acid oxidation
what does the cori cycle allow for
• The Cori cycle allows for anaerobic metabolism to take place in muscles.
describe how the cori cycle works
• Liver turns lactate into pyruvate using lactate dehydrogenase to remove it from the system and then pyruvate into glucose.
why does muscle run on fatty acids even during aerobic exercise
• Muscle can run on fatty acids even during aerobic exercise so there is enough glucose for the brain and other organs that have a large energy requirement
describe how glucose is produced from glycerol
- Glycerol produced from the breakdown of triglycerides (= triacylglycerols) stored in adipose tissue
- Enters as DHAP (dihydroxyacetone phosphate) in the middle of glycolysis/gluconeogenesis
describe how glucose can be produced from glycogenic amino acids
• Glucogenic amino acids can be broken down into pyruvate or oxaloacetate to then make glucose, all except for ketogenic Aa = leucine and lysine. .
How can the kidney perform gluconeogensis
- it uses glutamine
How do you control gluconeogensis
- control using glucagon, adrenaline and insulin
