Glycogenesis And Glycogenolysis

Question 1

Why is glycogen called a homopolysaccharide

Answer 1

Consistent glucose sugars polymerised

Question 2

Explain the structure of glycogen

Answer 2

High branched a glucose with 1,4 a bonds on backbone

1,6 a bond branches

Question 3

What are 3 reasons glucose can’t be monosaccharides within cells stored

Answer 3

Renal loss (excretion from the blood in urine)

Osmotic pressure inside cell causes lysis

Glycogen mobilises fast release of free glucose(due to branches)

Question 4

Why are branches needed for glucose supple

Answer 4

Allows degrading of glucose from multiple points at once increasing the rate

Question 5

What are the differences between liver and muscle glycogen

Answer 5

Muscle glycogen contains glucose 6 phosphate which is then used for muscle supply ONLY

Liver glycogen removes glucose for use for all cells - it controls blood glucose conc

Question 6

Which energy store out of fat protein and glucose/glycogen have most energy release

Answer 6

Fat

Question 7

When does glycogenesis occur in liver and muscle cells

Answer 7

When glucose is high in conc eg when you’re eating a meal

Question 8

What is the first step of glucose 6 phosphate conversion to glycogen

Answer 8

DIVERSION (away from glycolysis)

G 6 p is converted to G 1 P by

Phosphoglucomutase

Question 9

Once glucose 1 phosphate is produced by phosphoMUTASE , what happens

Answer 9

Activation step

UTP (uridine triphopshate)

Converted to UMP (1 monophosphate ) by cleaving a pyrophosphate

UMP then joins glucose 1 phosphate forming UDP glucose

Question 10

What converts UTP into UMP and then joins UMP to g1P to form UDP glucose

Answer 10

Pyrophosphate hydrolysis catalysed by pyrophosphorylase

Ump joined to glucose by UDP glucose pyrophosphorylase

Question 11

What happens once UDP glucose forms

Answer 11

Glucose is split from UDP + P

Forming free glucose

Joined to end of glycogen by glycogen synthase enzyme (non reducing end)

Question 12

What does glycogen synthase need to join free glucose to glycogen

Answer 12

Glycogenin- acts as a primer to start glycogen forming and prevents further glycogen depending on size

Question 13

When does glycogen start to branch (glycogen synthase moves from 14 bonds to 1,6)

Answer 13

After 10 glucose residues

Question 14

What happens to UDP + p when glucose is cleaved in polymerisation stage

Answer 14

It is recycled back into UTP for next glucose activation

Question 15

Which enzyme is needed to convert 1,4 a bonds to 1,6 a bonds in branching (glycogen synthase)

Answer 15

Amylo 1-4 —-> 1,6 transglycosylase

Question 16

What is glycogenolysis activated by and importent for

Answer 16

Activated by glucagon and epinephrine so that glucose can be released from liver cells to blood

Question 17

What happens first in glycogenolysis

Answer 17

Erosion of chain ends

Glycogen phosphorylase catalyses the release of a glucose 1 phosphate by addition of a free phosphate to the end glucose

This releases it from glycogen

Question 18

Which type of glycogen phosphorylase is active and inactive

Answer 18

A = active

B = inactive

Via allosteric control (a phosphate binds to enzyme to inactivate or activate it)

Question 19

Why is there remaining 4 glucose on a branch after glycogen phosphorylase activity

Answer 19

AS only fits up to the last 4 on branch remain

Question 20

Which enzyme removes the 3 glucose left by glycogen phosphorylase to add onto the other branch

Answer 20

Amylo 1-4 transferase enzyme

Question 21

Which enzyme is needed to cleave the last glucose on the 1,6 branch left by both glycogen phosphorylase and a 1,4 transferase

Answer 21

Amylo 1-6 glucosidase

Hydrolyses the 1,6 bond

Question 22

What happens to the free glucose 1 phosphate in glycogenolysis

Answer 22

It is converted into glucose 6 phosphate again by phosphoglucomutase

More useful eg for glycolysis

Question 23

What happens in the liver with the remaining glucose 6 phosphate

Answer 23

It is cleaved to produce free glucose for blood homeostasis

By glucose 6 phosphatase (regenerates glucose by addition of h20
cleaved it via hydrolysis)

Question 24

What is glycogen storage disease

Answer 24

Where enzymes that are in glycogenesis or glycogenolysis are disrupted

Causes muscle weakness and tiredness (no glucose in blood etc)

Question 25

What is type O Glycogen storage disease

Answer 25

Glycogen synthase in the liver is deficient

Can’t attach glucose form UDP glucose into glycogen branches

Free glucose molecules if turned into glucose can = hyperglycaemia

If stay as glucose 1 phosphate = hypoglycaemia as this can’t be broken down

Question 26

What is type 1 GSD

Answer 26

No glucose 6 phosphatase

G6P stays G6P and can’t be used as glucose in liver or blood

= hypoglycaemia

Question 27

What is type III GSD

Answer 27

Amylo 1-6 glucosidase deficiency (debranching enzymes)

The last glucose on branch not cleaved

Debranching ineffective

Glycolysis of the glucose is blocked = hypoglycaemia

Question 28

What is type IV GSD

Answer 28

Amylo both 1-4 and 1-6 glucosidase deficient

Left with long branches glycogen

Not efficient glycogenolysis

Hypoglycaemia

Question 29

What is type V GSD

Answer 29

Muscle glycogen phosphorylase A deficient
= no glycogen breakdown
=
No glucose release

= muscle weakness

Question 30

When does glycogenolysis not occur

Answer 30

Between meals- we use glycogen breakdown in emergencies only