W6 : Glycolysis and Glycogen Metabolism: Key Enzymes and Regulation

What is glycolysis?

A metabolic pathway that converts glucose into pyruvate producing ATP and NADH.

Where does glycolysis occur?

In the cytoplasm.

How many net ATP are produced from glycolysis?

2 ATP.

What is the final product of glycolysis?

Pyruvate.

How many ATP are used in glycolysis?

2 ATP.

How many ATP are produced in glycolysis?

4 ATP.

What are the three key regulatory enzymes of glycolysis?

Hexokinase, PFK-1, Pyruvate kinase.

What is the rate-limiting enzyme of glycolysis?

Phosphofructokinase-1 (PFK-1).

Why do irreversible steps regulate pathways?

They have large negative ΔG and control pathway direction.

What reaction is catalyzed by hexokinase?

Glucose to glucose-6-phosphate.

How is hexokinase regulated?

Inhibited by glucose-6-phosphate.

What is the function of glucokinase?

Phosphorylates glucose in the liver when glucose is high.

What reaction is catalyzed by PFK-1?

Fructose-6-phosphate to fructose-1,6-bisphosphate.

What are the activators of PFK-1?

AMP, ADP, fructose-2,6-bisphosphate.

What are the inhibitors of PFK-1?

ATP, citrate.

Why is PFK-1 important?

It is the committed and rate-limiting step.

What is the function of PFK-2?

Produces fructose-2,6-bisphosphate.

What role does fructose-2,6-bisphosphate play?

Activates PFK-1 and stimulates glycolysis.

What effect does glucagon have on PFK-2?

Decreases activity via phosphorylation.

What effect does insulin have on PFK-2?

Increases activity via dephosphorylation.

What reaction is catalyzed by pyruvate kinase?

Phosphoenolpyruvate to pyruvate.

What are the activators of pyruvate kinase?

Fructose-1,6-bisphosphate, insulin.

What are the inhibitors of pyruvate kinase?

ATP, glucagon.

What is feed-forward activation?

Upstream metabolite activates downstream enzyme.

What is the fate of pyruvate?

Converted to acetyl-CoA.

Which pathway does acetyl-CoA enter?

Citric acid cycle.

Is the conversion of pyruvate to acetyl-CoA reversible?

No, it is irreversible.

What is glycogen?

A branched polymer of glucose used for storage.

Where is glycogen stored?

In the liver and muscle.

Why is glycogen branched?

It allows rapid synthesis and breakdown.

Which enzyme breaks α-1,4 bonds in glycogen?

Glycogen phosphorylase.

Which enzyme removes branches from glycogen?

Debranching enzyme (transferase and α-1,6-glucosidase).

What are the products of glycogen breakdown?

Glucose-1-phosphate and glucose.

What is the conversion of G1P?

Glucose-6-phosphate.

What happens to G6P in muscle?

Enters glycolysis.

What happens to G6P in the liver?

Converted to glucose and released into blood.

What activates glycogen breakdown in muscle?

AMP, Ca²⁺, adrenaline.

What inhibits glycogen breakdown?

ATP, glucose-6-phosphate.

What role does calcium play in muscle?

Activates glycogen breakdown during contraction.

What activates glycogen breakdown in the liver?

Glucagon.

What inhibits glycogen breakdown in the liver?

Glucose.

What is the active form of glycogen phosphorylase?

Phosphorylated (phosphorylase a).

What is the active form of glycogen synthase?

Dephosphorylated.

Which enzyme is responsible for glycogen synthesis?

Glycogen synthase.

Why is UDP-glucose needed?

It activates glucose for polymer formation.

What is the effect of glucagon on glycogen metabolism?

Increases glycogen breakdown and decreases synthesis.

What is the effect of insulin on glycogen metabolism?

Increases glycogen synthesis and decreases breakdown.

What role does cAMP play?

Activates protein kinase A leading to phosphorylation.

What is reciprocal regulation?

Opposite control of synthesis and breakdown pathways.

Why is reciprocal regulation important?

It prevents energy waste.

What happens in a low energy state?

Glycolysis ON, glycogen breakdown ON.

What happens in a high energy state?

Glycolysis OFF, glycogen synthesis ON.