Glycogen Synthesis

What does glycgoen degradation yeild?

Glucose 1-phosphate

What does glycogen synthesis require?

UDP-glucose

what is the glucose synthesis equation?

Glucogen_n + UDP-glucose → glucogen_n+1 + glucose 1-phosphate

What is the glucose degridation equation?

Glycogen_n+1+ Pi → glycogen_n + glucose 1-phosphate

What is UDP-glucose?

An activated form of glucose

What is UDP-glucose in glycogen synthesis?

Glucose donor

What is the equation that synthesizes UDP-glucose?

Glucose 1-phosphate + UTP

What enzyme sythesizes UDP-glucose?

UDP-glucose phyrophosphorylase

What does glycogen synthase catalyze?

The transfer of glucose from UDP-glucose to a growing chain

What unit of UDP-glucose is attached to glycogen?

The activated glucosyl unit

How is the activated unit of UDP-glucose attached?

VIa an a-1,4-glycoside bond

What enzyme catalyzes the addition of an activated glucosyl unit of UDP-glucose to glycogen?

Glycogen synthase

What does glycogen synthase require to attach the activated glucose from UDP-glucose to glycogen?

An oligosaccharide of glucose residue as a primer

What is the glucose oligosaccharide primer synthezied by?

Glycogenin

What does glycogenin do?

Generate an oligosaccharied of 10-20 glucose residues to be a primer for glycogen synthase

What does glycogen synthase do after getting the oligosaccharide primer?

Extend it

What can glycogen synthase ONLY synthesize?

a-1,4 linkages

How is a branch greated?

VIa breaking an a-1,4 linkage and taking a block of about seven glucose residues and synthesizing an 1,6 linkage.

How is the 1,6 linkage synthesized?

The branching enzyme

What does branching do?

Incraeses the solubility and rate of the synthesis and degradation of glycogen

What end does synthase extend glycogen?

Both nonreducing ends, followed by more branching

What is glycogen synthesis inhibited by?

Glucagon and epinephrine signalling, the same that STIMULATE glycogen breakdown

What stimulates glycogen breakdown?

Protein kinase A

How does protein kinase A stimulate glycogen breakdown?

Phosphorylating and activating phosphorylase kinase

What inhibits glycogen synthesis?

Protien kinase A via phoshoyrlation

Glycogen synthase kinase

Phosphorylates and inhibits glycogen synthase

What is glycogen degradion activated by?

phosphorylation

What is glycogen synthesis inhibited by?

phosphorylation

When glycogen degradation is activated, what happens with phosphorylase b?

Phosphorylase b (less active) → phosphorylase a (active)

When glycogen synthesis is inhibited by phosphorylation what happens to synthase a and b?

synthase a (active) → synthase b (less active)

What does proteins phosphatase 1 (PP1) reverse?

Regulatory effects of kinases of glycogen metabolism

What does PP1 shift?

Glycogen metabolism from degradation to synthesis

PP1 does what to glycogen synthase b?

dephosphorylates glycogen synthase b, converting it to the more active form, stimulating synthesis

What does PP1 dephosphorylate?

Phosphrylase kinase and glycogen phosphorylase, inhibting glycogen degradation

What does PP1 inhibit?

Glycogen degradation, switching on phosphorylase b

What does PP1 stimulate?

Glycogen synthase, turning on syntahse a

After a meal, what is switched on?

Glycogen synthesis

During fasting or exercise, what is activated?

Glycogen breakdown

What does insulin do?

Stimulate glycogen synthesis by inactivating glycogen synthase kinase

What does glucagon and epinephrine simtulate?

Glycogen degradation

What does glucagon and epinephrine inhibit?

Glycogen synthesis

What does insuline stimulate?

Glycogen synthesis

What does insulin inhibit?

Glycogen degradation

Type 1 diabetes

autoimmune destruction of insuline producing cells

glucagon excess

in fasting mode

a shift in fuels usage from carbohydrates to fat

an accumulation of ketone bodies (diabetic ketosis)

Type 2 diabetes

Insuline resistance

Cori disease (III)

defective enzyme: a-1,6-glucosidase (debranching enzyme)

effects muscle and liver

Structure of liver and muscle glycogen is abnormal and glycogen amount is increased and mild hypoglycemia

Von gierke disease (type1)

Massive enlargement of the liver and severe hypoglycemia due to the lack of glucose 6-phosphatase in the liver

What is von gierke disease also caused by?

mutations in gene encoding the glucose 6-phosphate transporter

McArdle disease (Type V)

Defective muscle glycogen phosphorylase

Painful cramps when exercising