Glycolysis, Glycogenesis, and glycogenolysis (glycogen formation and breakdown)

What is the first step of Glycogenesis? What enzyme does this? Where in the muscle does it take place?

Hexokinase uses a phosphate from ATP, creating Glucose-6-phosphate and is stimulated by an increase in glucose (after a meal or during exercise)

All glycolytic pathways happen in the cytosol

What happens to Glucose-6-phosphate in the process of glycogenesis?

If glucose-6-phosphate isn’t needed in glycolysis for ATP production, it is converted into Glucose-1-phosphate by phosphoglucomutase

What happens to Glucose-1-phosphate in the process of Glycogenesis?

UDP-Glucose pyrophosphorylase synthesizes UDP-Glucose from G1P and UTP, providing the active building block for glycogen

What’s the role of Glycogenin in glycogeneis?

Glycogenin acts as primer if there are no available glucose branches for glycogen synthase to add new glucose on to. It attaches ~7-8 glucose residues to itself to start a glycogen branch

What’s the role of glycogen synthase?

Primary regulatory enzyme - it adds Glucose from UDP-Glucose to the non-reducing end of the glycogen chain, forming a-1-4 glycosidic bonds

What’s the role of the glycogen branching enzyme?

The branching enzyme creates branches in the glycogen chain by breaking a-1-4 glycosidic bonds and forming a-1-6 glycosidic bonds

What’s the role of glycogen phosphorylase?

Breaks off a-1-4 glycosidic bonds at the ends of glycogen branches, releases glucose-1-phosphate

What’s the role of the debranching enzyme?

moves a small block of glucose residues to a nearby straight chain and then clips off the final glucose at the a-1-6 glycosidic bond

What’s the role of phosphoglucomutase in glycogenolysis?

shifts phosphate group from 1st carbon back to the 6th carbon. Glucose-6-phosphate can then go down the glycolysis pathway

What happens in the first step of glycolysis? How is it different if it comes from glycogen?

phosphorylation - Glucose is converted into glucose-6-phosphate by hexokinase (uses 1 ATP)

If the process comes from glycogen it skips the first step as phosphoglucomutase turns it from glucose-1-phosphate to glucose-6-phosphate and vice versa

What happens to G6P in glycolysis?

Glucose-6-phosphate is isomerized by Glucose-6-phosphate isomerase and is turned into fructose-6-phosphate

What happens to fructose-6-phosphate in glycolysis?

Another phosphate is taken from ATP to make Fructose-1,6-bisphosphate using the enzyme Phosphofructokinase

RATE LIMITING ENZYME

What happens to Fructose-1,6-bisphosphate in glycolysis?

Fructose-1,6-bisphosphate is split into two molecules by the enzyme Aldolase;

1x Glyceraldehyde 3-phosphate

1x Di-hydroxy acetone phosphate

What enzyme converts Di-hydroxy acetone phosphate into Glyceraldehyde 3-phosphate?

Triose phosphate isomerase converts Dihydroxy acetone phosphate into a second Glyceraldehyde 3-phosphate by Triose phosphate isomerase

What happens to Glyceraldehyde 3-phosphate? (2 per glucose)

An inorganic phosphate is added to create 1,3-bisphosphoglycerate by the enzyme G3P Dehydrogenase and also creates 1 NADH per G3P (2 per glucose)

What happens to 1,3-bisphosphoglycerate?

A phosphate from 1,3-bisphosphoglycerate is transferred to ADP to make ATP by the enzyme phosphoglycerate kinase and you are left with 3 phosphoglycerate (2 ATP per glucose)

What happens to 3-phosphoglycerate?

Phosphoglycerate mutase moves the phosphate group from the third carbon to the second carbon, creating 2-phosphoglycerate

What happens to 2-phosphoglycerate?

A water molecule is removed by Enolase, creating the high-energy compound phosphoenolpyruvate

What’s the final step in glycolysis involving phosphoenolpyruvate?

The high energy phosphate compound is transferred from phosphoenolpyruvate to an ADP to make ATP by the enzyme Pyruvate Kinase. This leaves just pyruvate (end product of glycolysis)

2 ATP per glucose