Question

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Normal No Spacin Consider the various metabolie pathways that you have been studying to date- a) glycolysis b) gluconeogenesis e) glycogen synthesis d) glycogen breakdown e) fatty acid synthesis ) fatty acid breakdown g) ketone body production (to name a few) Please make a Table and in this table list 10 the various pathways, 2) the compartment of the cell in which they occur, 3) the major tissue(s) in which these pathways are important 4) the key rate limiting enzyme and the reaction it catalyzes 5) what happens to each of these enzymes (in terms of how active it is) immediately following a meal (within 3-4 hours) and 6) what happens to each of these enzymes (in terms of how active it is) 12 hours after the last meal.

Answer 1

Glycolysis - phosphofructokinase 1- conversion of fructose-6-phosphate to fructose-1,6-bisphosphate- Rise in blood glucose level after a meal activates intracellular liver fructose-2,6-BP which activates PFK-1 to start glycolysis
Long after a meal glucagon phosphorylates PFK2 which will convert fructose-1,6-bisphosphate to fructose-6-phosphate since the enzyme is bidirectional. In the absence of fructose-1,6-bisphosphate PFK1 is inactivated.
Gluconeogenesis- fructose 1,6-bisphosphatase - fructose 1,6-bisphosphatase converts fructose 1,6-bisphosphate to fructose 6-phosphate.
After a meal, since there is excess glucose in the blood there is no need of gluconeogenesis. PFK2 will produce Fructore 2,6 bisphosphate that will go and inhibit fructose 1,6-bisphosphatase.
Long after a meal glucagon Phosphorylates PFK-2 there by inactivatingit and Fructore 2-6 bisphosphate level goes down.Now Fructose 16 Bisphospahtase is free to start gluconeogenesis

Glycogen synthesis – glycogen synthase. Converts UDP-glucose to glycogen. After a meal rise in blood glucose level stimulates glycogen production in liver. After a long time Protein kinase A phosphorylates Glycogen synthase there by inactivating it.

Glycogen breakdown- glycogen phosphorylase. Converts glycogen to limit dextran. Glucagon activates glycogen phosphorylase through a series of steps 12 hours after taking a meal and when the body is in need of glucose.
Fatty acid synthesis- Acetyl-CoA carboxylase. Conversion of acetyl-CoA to malonyl-CoA . After a meal insulin activates by dephosphorylating this enzyme using a phosphatase and stimulates fatty acid synthesis. Long after the meal glucagon and epinephrine activates protein kinase A which in turn will phosphorylate the phosphatase leaving the Acetyl-CoA carboxylase in phosphorylated deactived form
Ketone body production- Hydroxymethylglutaryl CoA synthase or HMG CoA synthase- –Catalyses the generation of HMG-CoA from acetoacetyl-CoA and acetyl-CoA.
Production as well as the activity of HMG-CoA reductase peak 4 to 6 hours after the a meal