BIOC L3 - carbohydrate metabolism

What is the key hormone in the fed state?

insulin - interacts with receptor to cause tissues to take up glucose

What are insulin independent tissues?

brain and liver

What actions occur in the fed state stimulated by insulin (glucose)?

glycolysis and glycogenesis

What is the key hormone in the fasted state?

glucagon

What processes does glucagon stimulate (glucose) and what does this process utilise?

gluconeogenesis - making new glucose from 3 carbon sources such as amino acids, lactate and glycerol

What is the major transport pathway for absorption of glucose, TAGs and AAs

transcellular pathway

What happens to our macronutrients under aerobic conditions?

everything feeds into or is converted in Acetyl CoA and this is fed into the CAC to make reduced coeznymes for the ETC

How do adrenaline and glucagon act on each tissue type?

adipose: adrenaline and glucagon act to break down stored fat in lipolysis. muscle: adrenaline and glucagon break down stored glycogen in glycogenolysis. liver: break down glycogen in glycogenolysis and start making new glucose in gluconeogenesis

What is the primary driver of glycolysis?

increase in blood glucose levels

How is glycogen synthesised?

glucose broken down into G6P in glycolysis, converted to G1P and UDP is adeed forming UDPG which can be added to glycogen

What is the role of glycogen phosphorylase?

breaks down glycogen in the liver

What is the role of glycogen synthase?

formation of glycogen in the liver

Why can't glycogen broken down in muscle be released into the blood?

muscle does not have the glucose-6-phosphatase enzyme so glycogen can only be broken down into G6P

What is glycogenin?

when starting to make glycogen but no branch points yet

What is proglycogen?

premature glycogen molecule with branch points but still a small molecule

What is macroglycogen?

large molecule, glucose is broken off and added on from both ends at once

What do branches do on a glycogen molecule?

incease the rate at which glucose can be added and removed

What are the 2 stages of synthesis?

chain extension, branching

How many reactions in gluconeogenesis are different from glycolysis?

3 reactions: pyruvate -> PEP, F1,6BP -> F6P, G6P -> glucose

How is reaction between F1, 6BP -> F6P mediated?

enzymes for reaction are always active but are activated or inhibited depending on whether insulin or glucagon are present

How do amino acids and TAGs feed into the glycolysis/glycogenolysis pathway?

when decarboxylated and rearranged form pyruvate or oxaloacetate which feed in at the end of the pathway and lacate can also be converted to pyruvate, glycerol from TAGs feeds in around the middle of the pathway

What tissues are involved in gluconeogenesis?

liver completes gluconeogenesis and some in kidney

Why are we more prone to infection in a fasted state?

immune cells are broken down for AAs to feed into gluconeogenesis