Such as what does happen in step 1,3,10 and how those things occurred in each st

Question

Such as what does happen in step 1,3,10 and how those things occurred in each steps and why Please help me to understand each detail in each step Thanks Chapter 15-Metabolic Regulation: Glucose and Glycogen Different methods of regulating enzymes Requlation of glvcolysis (Step 1) Isozymes of hexokinase in liver and muscle reflect their different roles in glucose IS: metabolism. Muscle: glucose consumption Liver: glucose homeostasis In muscle: low Km, almost always at Vmax, inhibited by g-6-p. - In liver: high Km. Sequestered until high levels of glucose present. Sigmoidal curve (Step 3) Phosphofructokinase Allosteric Inhibitors: ATP, Citrate (what do these signal?) Allosteric Activators: ADP, AMP, F2,6BP (Step 10) pyruvate kinase Allosteric Inhibitors: ATP, acetyl-CoA Allosteric Activators: F 1,6 BP In liver only: glucagon results in phosphorylation of PK making it in inactive (why would this be? -

Explanation / Answer

Given Steps 1,3and 10 can be understand by detailed analysis of Glycolysis.so below is the detailed explanation of Glycolysis.

Regulation of enzymes in Glycolysis is said to occur in two phases:

1. The Preparatory Phase: From glucose till formation of Glyceraldehyde 3-Phosphate (GADP).
2. The Pay-off Phase: From Glyceraldehyde-3-Phosphate (GADP) to the final product pyruvate.

The Preparatory phase -

In this stage of the cycle, ATP or energy is actually consumed and is hence also known as the investment phase of glycolysis.

Step 1-(hexokinase)

involves the conversion of glucose to glucose-6-phosphate (G6P) with the help of the enzyme hexokinase and the consumption of 1 molecule of ATP.

The different hexokinase isozymes of liver and muscle reflect the different roles of these organs in carbohydrate metabolism: muscle consumes glucose, using it for energy production, whereas liver maintains blood glucose homeostasis by removing or producing glucose, depending on the prevailing glucose concentration.

Step 2-

involves the rearrangement of glucose-6-phosphate to fructose-6-phosphate (F6P) with the help of the enzyme phosphohexose isomerase in a reversible manner. Fructose can directly enter the glycolysis pathway at this point.

Step 3-(phosphofructokinase)

involves the phosphorylation of fructose-6-phosphate to fructose-1,6-biphosphate (F1,6BP) by the use of 1 molecule of ATP and the enzyme phosphofructokinase-1 (PPK1). This phosphorylation step destabilizes the molecule and helps drive the next reaction which ensures breakdown of the molecule to a 3-carbon unit.

Step 4-

involves the breakdown of fructose-1,6-biphosphate (6 carbons) to two molecules of 3-carbon units i.e. glyceralde 3-phosphate (GADP) and Dihydroxyacetone phosphate (DHAP). The GADP can be interconverted to DHAP by enzyme triose phosphate isomerase.

The Pay Off phase -

In this stage of the cycle, ATP or energy is produced either in the form of ATP alone or in the form of NADH + H+ which can be later converted to ATP via the electron transport chain (ETS). In this since energy is restored it is known as the pay-off phase of glycolysis. All steps in this phase occur with 2 molecules of the substrates each as indicated in the brackets by the name of the molecules.

Step 1-

involves the dehydrogenation of glyceraldehyde-3-phosphate (GADP) to 1,3-biphophoglycerate (1,3BPG) by the use of 2 molecules of inorganic phosphate (Pi) with the production of 2 molecules of NADH + H+ in the presence of the enzyme glyceraldehyde 3-phosphate dehydrogenase.

Step 2-

In this step dephosphorylation of 1,3-biphosphoglycerate (1,3BPG) to 3-phospoglycerate (3PG) produces 2 molecules of ATP by the enzyme phosphoglycerate kinase.

Step 3-

Involves the isomerisation of 3-phosphoglycerate (3PG) to 2-phosphoglycerate (2PG) by the enzyme phosphoglycerate mutase in a reversible manner.

Step 4 -

involves the enolization of 2-phosphoglycerate (2PG) to phosphoenolpyruvate (PEP) with the loss of one molecule of water in the presence of enzyme enolase.

Step 5-(pyruvate kinase)

is the final step of the glycolysis pathway and it involves the dephosphorylation of the phosphoenolpyruvate (PEP) to pyruvate by enzyme pyruvate kinase to produce 2 more molecules of ATP.

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