13. Post Absorption Processing of Carbohydrates Flashcards
What is the hormonal response to being in the fed state?
Increased insulin
Decreased glucagon
What is the response of organs to being in the fed state?
Liver makes glycogen, proteins, TAGs
Adipose makes TAGs
Muscle makes protein
What is the hormonal response to being in the fasting state?
Decreased insulin
Increased glucagon and adrenaline
What is the liver’s response to the fasting state?
Glycogenolysis
Gluconeogenesis
B-oxidation
Ketogenesis
What is adipose tissue’s response to the fasting state?
Lipolysis
What is the muscle’s response to the fasting state?
Use FAs and ketones as fuel
Proteolysis to supply the liver with AAs
What is gluconeogenesis?
Synthesis of glucose from lactate, pyruvate and glycerol
What is gluconeogensis stimulated by?
Glucagon
What enzymes are involved in gluconeogenesis?
Pyruvate carboxylase
PEP carboxykinase
Fructose-1,6-bisphosphate
Glucose-6-phosphatase
What is the structure of glycogen?
a-D glucose units joined by a-1,4 glycosidic bonds
What type of bonds attach chains to glycogen?
a-1,6 glycosidic bonds
What is the function of glycogen synthase?
Adds units to the non-reducing ends of growing chains of glucose
What enzyme is used if there is no remaining glycogen?
Glycogenin
What adds branches to glycogen?
Branching enzyme
What are the steps in glycogenolysis?
- Glycogen phosphorylase cleaves a-1,4 glycosidic bonds
- Glucose units are released as glucose-1-phosphate
- GP stops 4 glucose residues before each branch point, creating limit dextrins
- Branches are removed by debranching enzyme
What converts glucose-1-P to glucose-6-p?
Phosphoglucomutase
What happens to glucose-6-P in the liver?
Converted to glucose by glucose-6-phosphatase
Requires glucose-6-P translocase
Released into the bloodstream
What happens to glucose-6-P in muscle?
Goes into glycolysis
What is the allosteric regulation of glycogen breakdown?
Glucose-6-P increases glycogen synthase and decreases glycogen phosphorylase
Ca++ released by muscle contraction, increased AMP (muscle anoxia) and low ATP increase glycogen phosphorylase
What are the effects of glucagon and adrenaline on glycogen breakdown?
Activate cAMP dependent PkA to cause phosphorylation
Activates GP and inactivates GS to cause glycogen breakdown
What effect does insulin have on glycogen breakdown?
Causes dephosphorylation
Increase GS, decrease GP
Glycogen synthesis
What enzyme is deficient in McArdle Disease?
Muscle Glycogen Phosphorylase Deficiency
What are symptoms of McArdle Disease?
Muscle fatigue
Myoglobinuria
What enzyme is deficient in Von Gierke’s Disease?
Glucose-6-Phosphatase
What are symptoms of Von Gierke’s Disease?
Hypoglycaemia
Lactic acidosis
Ketosis
Hepatomegaly
