Question

Describe “hub” molecules acetyl CoA and pyruvate that serve different pathways. Explain metabolic regulation favoring metabolic pathway choices leading to and from hub molecules. Describe how C.A.C. serves as a “hub “pathway. Use picture as a reference.

Pyruvate Glucose Fatty acids sterols pyruvate carboxylase Acetyl-CoA PEP carboxykinase Glutamine Citrate Phosphoenolpyruvate (PEP) Proline Arginine Oxaloacetate PEP carboxylase Citric acid cycle a-Ketoglutarate Malate Glutamate Aspartate Asparagine Serine Glycine Cysteine malic enzyme Purines Succinyl-CoA Phenylalanine Pyrimidines Pyruvate Tyrosine Tryptophan Porphyrins heme Figure 16-16 Lehninger Principles of Biochemistry, Sicth Edition 2013 W, H, Freeman and Company

Answer 1

Pyruvate and acetyl CoA are very important in our body they are used when we are low in ATP concentration in our body.
Glucose is converted to pyruvate through glycolysis and 2 moles of ATPs are produced which gives us energy.
Then this pyruvate is converted into acetyl CoA beacuse pyruvate cannot enter in the mitochondrial matrix and acetl CoA can. Then this acetyl CoA generates 2 moles of ATP and 10 moles of NADH and 2 moles of FADH2 via citric acid cycle (C.A.C.). These NADH and FADH2 can further be converted into ATP via electron transfer process. So total 38 moles of ATP can be generated with one mole of glucose molecule through glycolysis, C.A.C. and electron transfer process.These NADH cannot enter in the mitrocondrial matrix so for this purpose malate-asparatate shuttle is used.
So from pyruvate many compounds can be generated which are important in many metabolic pathways and regulations. pyruvate can be converted to acetl CoA which is used in C.A.C. It can be converted to oxaloacetate with the help of pyruvate carboxylase enzyme, which is also used in kreb's cycle. Malate can also be generated from pyruvate using malic enzyme.
Acetyl CoA is used in the citric acid cycle for the synthesis of ATP molecule and in this process many molecules are from like citrate, alpha-keto glutarate, succinyl CoA. malate etc. Acetyl CoA can also be generated from the beta-oxidation of fatty acids.
As given in the picture one can see the different processes regulating by acetyl CoA and pyruvate using different kinds of enzymes.
C.A.C. serves as a hub pathway because the different molecules generated during this cycle can be used in different kind of other metabolic reactions like alpha-keto glutarate can be used in the malate-asparatate shuttle, oxaloacetate can convert intp PEP which can further convert into glucose.