L28 Glycogen metabolism

Question 1

Why not just store glucose?

Answer 1

• Renal loss

* Glucose is osmotically active (would affect osmotic pressure)

Question 2

Glycogen is a:

a) highly branched monosaccharide
b) unbranched polysaccharide
c) highly branched homopolysaccharide
d) highly branched heteropolysaccharide

Answer 2

c) highly branched homopolysaccharide

Question 3

Glycogen chains are linked by α-1,4-glycosidic bonds. Branches are linked by…

Answer 3

α-1,6-glycosidic bonds

Question 4

The largest glycogen stores in the body are found in…

Answer 4

Muscle

Question 5

The liver, by weight, is:

a) 10% glycogen
b) 2% glycogen
c) 6% glycogen
d) 20% glycogen

Answer 5

a) 10% glycogen

Question 6

Fat stores energy more efficiently, but requires…

Answer 6

Oxygen

Question 7

The creation of glycogen is known as…

Answer 7

Glycogenesis

Question 8

The breakdown of glycogen stores for use is known as…

Answer 8

Glycogenolysis

Question 9

Step 1 of glycogenesis is…

Answer 9

Diversion

Question 10

In diversion, glucose-6-phosphate is diverted from…

Answer 10

Glycolysis

Question 11

In diversion, G-6-P is converted to G-1-P by the enzyme…

Answer 11

Phosphoglucomutase

Question 12

Step 2 of glycogenesis is…

Answer 12

Activation

Question 13

In activation, G-1-P is converted to UDP-glucose by…

Answer 13

UDP-Glucose pyrophosphate (with the addition of Uridine triphosphate)

Question 14

Step 3 of glycogenesis is…

Answer 14

Polymerisation

Question 15

In polymerisation, UDP-glucose is converted to…

Answer 15

Glycogen by glycogen synthase (which removes UDP)

Question 16

In polymerisation, glucose is added to the glycogen chain with a…

Answer 16

α-1,4-glycosidic bond

Question 17

Step 4 of glycogenesis is…

Answer 17

Glycogen branching

Question 18

In glycogen branching, branches are added by the enzyme…

Answer 18

Amylo-(1,4 →1,6)-transglycosylase

Question 19

The size of glycogen is limited by the decreasing activity of…

Answer 19

Glycogenin (over distance)

Question 20

Glycogenolysis starts with the…

Answer 20

Erosion of chains

Question 21

Glycogen phosphorylase converts glycogen monomers back into…

Answer 21

G-1-P

Question 22

Glycogen phosphorylase is stored…

Answer 22

With glycogen in an inactive form

Question 23

Glycogen phosphorylase is regulated by (2)…

Answer 23

Allosteric and hormonal control

Question 24

Glycogen phosphorylase in the liver is regulated by glucose levels. In the muscle it is regulated by the level of…

Answer 24

AMP vs ATP

Question 25

Why can’t glycogen phosphorylase process chains shorter than 4 residues in length?

Answer 25

The active site is situated far back in the enzyme

Question 26

Step 2 of glycogenolysis is…

Answer 26

Debranching

Question 27

Debranching occurs via the enzymes (2)…

Answer 27

α-(1-4)-transglycosylase (transfers all but one of the branch to the main chain)

α-(1-6)-glucosidase (releases the glucose)

Question 28

Step 3 of glycogenolysis is…

Answer 28

Recovery

Question 29

In recovery, G-1-P generated from glycogen is converted into…

Answer 29

G-6-P

Question 30

In glycogenolysis, phosphoglucomutase converts…

Answer 30

G-1-P to G-6-P

The reverse of its action in glycogenesis

Question 31

Glycogen is synthesised and broken down by…

Answer 31

Two separate pathways

Question 32

Glycogen storage diseases (GSDs) (4)…

Answer 32

• Type 0 (liver glycogen synthase deficiency)
• Type I (Von Gierke’s disease)
• Type III (Cori’s disease)
• Type IV (Andersen’s disease)

Question 33

Type 0 GSD results in an…

Answer 33

Inability to synthesise glycogen and is thus incompatible with life ☠️

Question 34

Type I GSD (Von Gierke’s disease) is a…

Answer 34

Glucose-6-phosphatase deficiency which sometimes results in death

Question 35

Type III GSD (Cori’s disease) is an…

Answer 35

Amylo-1,6-glucosidase deficiency which causes enlarged liver and hypoglycemia

Question 36

Type IV GSD (Andersen’s disease) results in a…

Answer 36

Lack of glycogen branching