Gluconeogenesis (lecture 27) Flashcards
lab based definition of of blood glucose homeostasis
plasma glucose of 4-6 mol/L
clinical definition of blood glucose homeostasis
maintenance of blood sugar levels within narrow physiological limits
balance of insulin & glucagon
why does blood glucose need to be maintained?
glucose is the preferred energy source
only fuel for RBCs
causes problems if not maintained
what is hypoglycaemia?
when glucose levels are low - below 4 mol/L occurs • during starvation • during & after exercise • commonly linked with insulin overdose
what is hyperglycaemia?
when glucose levels are high
lots of glucose draws water out of our cells & tissues
excess blood glucose causes by insulin resistance / lack of insulin
occurs
• after a meal
• inadequate administration of insulin
what is gluconeogenesis?
creation of new glucose
enables us to preserve glycogen for emergencies
mainly in the liver
4 sources for gluconeogenesis
pyruvate/lacate
glycerol
CAC intermediaries
amino acids
what is the cori cycle?
when we exercise anaerobically we get a build up of lactate as the body cannot do oxidative phosphorylation
cori cycle helps to remove lactate
processed is reversed in the liver
lactate causes damage when transported in the blood
what is the alanine cycle?
conversion of pyruvate to alanine
in muscle, when O2 is available, lactate can be converted to pyruvate
ammonia groups added to pyruvate to form alanine which can be transported in the blood
pyruvate + NH3 = alanine
ammonia removed in liver allowing alanine to be converted back to pyruvate
what are the 3 energetically unfavourable reactions in the reversal of glycolysis
pyruvate to PEP (phosphoenolpyruvate)
fructose-1,6-bisphosphate to fructose-6-phosphate
glucose-6-phosphate to glucose
pyruvate to PEP
pyruvate converted to oxaloacetate by pyruvate carboxylase - requires vitamin biotin to orientate active site correctly
1 ATP needed
oxaloacetate is charged so cannot diffuse through mitochondrial membrane
malate dehydrogenase converts it to malate to allow it to diffuse out of the mitochondria
isoenzyme for malate dehydrogenase converts it back to oxaloacetate once outside mitochondria
oxaloacetate converted to PEP by PEP carboxykinase which requires GTP
fructose-1,6-bisphosphate to fructose-6-phosphate
fructose-1,6-bisphosphatase enzyme used
water used
phosphate released
glucose-6-phosphate to glucose
glucose-6-phosphatase used
water used
phosphate released
what do phosphatases do?
chop off a phosphate group
what is the cost of gluconeogenesis?
4ATP and 2GTP
uses 3x more energy than glycolysis
