Glycogenolysis/Glycogenesis

Question 1

Glycogenesis

Answer 1

the production of glycogen from glucose

Question 2

Glycogenesis process (4 steps)

Answer 2

(starts with glucose-6-phosphate)

1. phosphate on C6 moves to C1
2. glucose-1-phosphate + UTP = UDP-glucose
3. glucose-phosphate bond broken and the energy produced is sued to add the glucose to the glycogen chain
4. enzyme breaks bonds between 6/7th glucose and reattaches further down the chain = branching

Question 3

What enzyme is involved in glycogenesis step one?

Answer 3

phospho,gluco,mutase

mutase = rearranging enzyme

Question 4

What enzyme is involved in glycogenesis step two?

Answer 4

UDP-glucose pyrophosphorylase

~ reversible reaction (goes forward)

Question 5

What enzyme is involved in glycogenesis step three?

Answer 5

glycogen synthase

~ regulated by blood-sugar lvls + allosteric regulation

Question 6

What enzyme is involved in glycogenesis step four?

Answer 6

branching enzyme

Question 7

Glycogenolysis

Answer 7

breakdown of glycogen to glucose

Question 8

Glycogenolysis process (4 steps)

Answer 8

1. a’(1-4) glycosidic bond between end two glucoses is broken by Pi addition
2. branches are removed when they reach 4 glucose long (enzyme needs space)
3. glucose-1-phosphate –> glucose-6-phosphate
4. glucose-6-phosphate –> glucose

Question 9

What enzyme is involved in glycogenolysis step one?

Answer 9

glycogen phosphorylase

~ regulated step

Question 10

What enzyme is involved in glycogenolysis step two?

Answer 10

oligo (a’1-4 –>a’1-4) glucantransferase = moves end 3 glucose to another branch
a’(1-6) glucosidase = removes final glucose

Question 11

What enzyme is involved in glycogenolysis step three?

Answer 11

phospho,gluco,mutase

Question 12

What enzyme is involved in glycogenolysis step four?

Answer 12

glucose-6-phosphatase

~ found only in liver + kidneys

Question 13

Allosteric regulation

Answer 13

~ glycogenesis (glycogen synthase) - increases activity
~ glycogenolysis (glycogen phosphorylase) - decreases activity
~ reciprocal control
~ both controlled by glucose-6-phosphate binding to their allosteric sites

Question 14

Glycogenesis - hormonal regulation - ACTIVATION

Answer 14

1. insulin binds to receptors on hepatocytes
2. causes phosphatase to remove a Pi and activate glycogen synthase
3. adds glucose to glycogen

Question 15

Glycogenesis - hormonal regulation - INHIBITION

Answer 15

1. glucagon/adrenaline binds to receptors
2. activates cAMP which activates a kinase
3. kinase adds Pi from ATP to glycogen synthase, inactivating it

Question 16

Glycogenolysis - hormonal regulation - ACTIVATION

Answer 16

1. glucagon/adrenaline binds to PM receptors
2. activates adenylate cyclase = turns ATP –> cAMP
3. cAMP activates a kinase
4. kinase adds a Pi from ATP into phosphorylase kinase, activating it
5. phosphorylase kinase adds Pi from ATP to glycogen phosphorylase, activating it
6. glycogen + pi -> glucose-1-phosphate

Question 17

Glycogenolysis - hormonal regulation - INACTIVATION

Answer 17

1. insulin binds to receptor

2. phosphatase removes a Pi from phosphorylase kinase and glycogen phosphorylase, inactivating them

Question 18

Protein phosphatase is activated/inactivated by …

Answer 18

activated = presence of glucose
inactivated = protein kinase