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What is the optimum glucose concentration of the blood?

5 mmol/L

What are the 2 major sources of blood glucose?

diet

breakdown of hepatic glycogen stores

Glycogenesis

glycogen biosynthesis

Glycogenlysis

glycogen breakdown

Is glycogenesis endergonic or exergonic?

endergonic

What is the primer for glycogenesis?

glycogenin

What is the purpose of UDP-glucose?

the synthesis of sugar nucleotides is irreversible; it cannot be diverted to other pathways such as glycolysis

nucleotide moiety possesses groups that can undergo enzymatic noncovalent interactions and thus contributing to catalytic activity

What is the key regulatory enzyme of glycogenesis? Why?

glycogen synthase

UDP glucose is involved in glycolipid and glycoprotein synthesis

What type of bonds are formed by glycogen synthase?

alpha 1-4 glycosidic linkages in the main chain

What is the purpose of branch points (2)?

increase solubility of glycogen molecule

create numerous non-reducing ends for rapid synthesis and degradation

What is the rate-limiting step in glycogenolysis?

glycogen phosphorylase

What is the function of glycogen phosphorylase?

removes a single glucose-1-phosphate from the glycogen core

What enzyme rearranges glucose-1-phosphate to glucose-6-phosphate?

phosphoglucomutase

How does glucose leave the liver?

GLUT2

In what organelle is hepatic glucose-6-phosphatase located?

ER lumen

Name 2 allosteric activators of muscle glycogen phosphorylase

AMP

Ca2+

Name an allosteric inhibitor of muscle glycogen phosphorylase

glucose-6-phosphate

Describe the pathway of muscle activation and glycogenolysis

Beta-receptor (epinephrine)

cAMP

protein kinase A

phosphorylase kinase (phosphorylated)

glycogenolysis (glycogen phosphorylase a)

glycolysis

fructose-1,6-phosphate

TCA

oxidative phosphorylation

Does glucagon affect muscle cells?

glucagon has no effect on muscle

Where is glucagon produced?

pancreatic alpha-cells

Where is insulin produced?

pancreatic beta-cells

Where is epinephrine produced?

adrenal medulla

Name an activator of hepatic glycogen synthase

glucose-6-phosphate

Name 3 inhibitors of hepatic glycogen phosphorylase

glucose-6-phosphate

ATP

glucose

When is liver phosphorylase A active?

phosphorylated

When is liver phosphorylase inactive?

dephosphorylated

What type of receptor is the glucagon receptor?

G protein coupled receptor

Glycogen storage disease

inherited enzyme deficiencies that lead to the storage of glycogen in abnormal amounts and sometimes with an abnormal structure

Which GSD is caused by glucose-6-phosphatase deficiency?

Von Gierke's disease (type I)

Which GSD is caused by lysosomal alpha-1,4-glucosidase deficiency?

type 2: Pompe's disease

Name 2 characteristics of hepatic glycogen storage diseases

hypoglycemia

hepatomegaly

Name 2 characteristics of myopathic (muscle) glycogen storage diseases

muscle weakness and cramps

Which GSD has the following characteristics? glycogen of normal structure accumulates in lysosomes

blood glucose is normal

liver, muscle & heart affected cardiomegaly can occur

Pompe's (type II)

McArdle's disease (type V)

muscle glycogen phosphorylase deficiency (or absence)

abnormally high glycogen stores in muscle w/normal structure

diminished exercise tolerance-blood lactate levels don't rise during exercise

liver enzymes are normal

Does McArdle's disease affect liver enzymes?

no

What is myoglobinuria? Which GSD is associated with myoglobinemia?

myoblogin in urine

McArdle's disease

What blood marker would suggest McArdle's disease?

increased CKMM

What is the prognosis for McArdle's disease?

avoid strenuous exercise

Tarui's disease (type VII)

deficiency of PFK-1, affects skeletal muscle & RBC's

symptoms similar to type V (McArdle's) ---> but also causes erythrocyte HEMOLYSIS

ability to obtain energy from glucose & glycogen impaired

Symptoms of what GSD are similar to Tarui's disease

Type V: McArdle's disease

Name the 4 GSD's affecting the Liver

type I: von Gierke

type III Cori

type IV: Andersen

type VI: Hers

type Ib glycogen storage disease

deficiency in glucose-6-phosphate transporter

Why does hypoglycemia leads to excessive TAG degradation in adipose tissue?

insulin levels drop, leading to activation of hormone-sensitive lipase, free fatty acids for energy

What changes occur in blood chemistry for type I GSD?

hypoglycemia

hyperlipidemia & ketosis

hyperurecemia leading to gout

Cori's (Type III) GSD

defect or absence of DEbranching enzyme

accumulation of abnormal glycogen - w/short outer branches

Anderson's (type IV) GSD

defect or absence of Branching enzyme

abnormal glycogen - few branch points, so less soluble than normal

liver treats abnormal glycogen as 'foreign' - produces large amounts of fibrous tissue - hepatomegaly

Hers (type VI) GSD

absence or deficiency of Hepatic (liver) glycogen phosphorylase deficiency - muscle enzyme normal

Symptoms of Hers disease

high levels of hepatic glycogen - hepatomegaly

Symptoms are similar to Type I (Von Gierke's) only milder

Why is hypoglycemia mild in Hers disease?

liver can still make glucose from pyruvate

What is the function of glycogen phosphorylase?

release glucose-1-phosphate by breaking alpha-1,4-bonds

Describe the structure of glycogen

alpha(1,4) glycosidic bonds

alpha(1,6) glycosidic branches every 8-12 residues

What transfers -OH group to glycogenin?

tyrosine residue

To which end are glucose unit added?

non-reducing ends

What is UDP-glucose?

group transfer reagent carrying an activated form of glucose

Glucokinase requires which co-factor?

Mg2+

What enzyme catalyzes the reaction from glucose-6-phosphate to glucose-1-phosphate?

phosphoglucomutase

What enzyme removes branches from the glycogen core?

debranching enzyme

In what situation does glycogenolysis occur in muscle tissue?

prolonged exercise

Describe the dual stimulation of muscle activation and glycogenolysis

Ca2+-calmodulin complex and AMP on phosphorylase kinase

AMP stimulates PFK-1 and and thus glycolysis

AMP stimulates phosphorylase kinase

Are muscle and liver tissues affected by insulin?

yes, both

Hypoglycemia will lead to secretion of what hormone(s)?

glucagon

adrenaline

Hyperglycemia will lead to secretion of what hormone(s)?

insulin

How does glucagon affect glycogenolysis?

rapid activation

How does insulin affect glycogenolysis?

inhibitory

How does adrenaline affect glycogenolysis?

rapid activation

In glycogen synthesis is hepatic glycogen synthase phosphorylated or de-?

dephosphorylated

In glycogenolysis, is hepatic glycogen phosphorylase phosphorylated or de-?

phosphorylated

Name an activator of muscle glycogen synthase

glucose-6-phosphate

Name 2 activators of muscle glycogen phosphorylase

Ca2+

AMP

Name 2 inhibitors of glycogen phosphorylase

glucose-6-phosphate & ATP

Explain what happens when glucagon binds to its receptor (up until phosphorylation events)

glucagon binds to its receptor, causing GDP to become GTP; this activates the g-protein

adenylyl cyclase creates cAMP from ATP

cAMP activates protein kinase A

Describe the effects of protein kinase A on Inhibitor - I

protein kinase A phosphorylates inhibitor-I, which becomes active

inhibitor - I inhibits phosphoprotein phosphatase, which is responsible for converting glycogen phosphorylase to its inactive form

Describe the effects of protein kinase A on phosphorylase kinase

protein kinase A phosphorylates phosphorylase kinase-b, which activates the enzyme

phosphorylase kinase-a phosphorylates glycogen phosphorylase-b, which becomes active

glycogen phosphorylase-a can then activate glycogenolysis

Describe the effects of protein kinase A on glycogen synthase

protein kinase A phosphorylates glycogen synthase-a, which becomes inactive

In muscle, how can phosphorylase kinase be activated without phosphorylation?

Ca2+ binds to the calmodulin subunit of phosphorylase kinase, activating it without phosphorylation

What is the main mechanism behind anti-glucagon effects?

dephosphorylation of glycogen synthase (activates the enzyme)

For McArdle's disease, would blood lactate rise during strenuous exercise?

no

What is the rate-limiting step of glycogen biosynthesis?

formation of the alpha-1,4-bond with the primer at the non-reducing end

UDP-glucose + (glycogen)n <---> (glycogen)n+1 + UDP

Mneumonic for the 7 GSD

"Viagra Pills Cause A Mostly Happy Time": Von Gierke's, Pompe's,
Cori's, Anderson's, McArdle's, Her's, Tarui's

Why does hyperurecemia lead to gout in type I GSD?

increased activity of the PPP --> increased purine synthesis

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