Glycogen

Question 1

Glycogen

Answer 1

1) a glucose polymer (up to 100,000 molecules of glucose/ molecule of glycogen)
2) Homopolysaccharide (because only made of glucose)

Question 2

Backbone of glycogen

Answer 2

D-glucose are linked together by O-glycosidic bonds

Question 3

Glycosidic bond

Answer 3

A bond linking a sugar with another molecule (in glycogen, this other molecule is another glucose)
(O-, N- and P- glycosidic bond)

Question 4

α1->4 intra-chain bond vs α1->6 inter-chain bond

Answer 4

Question 5

Reduinng sugar characteristics:

Answer 5

1) are sugars capable of acting as a reducing agent since they still have a free aldehyde or ketone group.
2) needs to have an hemiacetal or hemiketal group.

Question 6

Reducing agent

Answer 6

A compound who gives electrons to an oxidizing agent.

Question 7

Reducing Sugar quality

Answer 7

If the anomeric carbon (alpha or beta involved in the bond) is part of an hemiacetal or hemiketal, the corresponding carbohydrate has the possibility of being converted to its linear form and thus, displays an aldehyde or ketone group

Question 8

Hemiacetal

Answer 8

A carbon which is part of an ether bond (R-O-R’) but is also attached to an alcohol (OH) is called an hemiacetal. Hemiacetal are derived from aldehyde (e.g. glucose).

Question 9

Hemiketal

Answer 9

Carbon which is part of an ether bond (R-O-R’) but is also attached to an alcohol (OH). Hemiketal are derived from ketone (e.g. fructose).

Question 10

Anomeric Carbon

Answer 10

A carbon at the center of an hemiacetal or hemiketal functional group

Question 11

Picture explanation of hemiacetal and anomeric carbons

Answer 11

Both bottom are hemiacetal (one on right is beta bond because OH farther away from CH2OH whereas Beta is )H closer to CH2OH)

• Carbon in bottom can be reduced back to linear form with anomeric carbon at top of picture

Question 12

Explanaition of reducing ends

Answer 12

On one side of a sugar there is a reducing end and a non-reducing end = the black circle (top = anomeric carbon) forms a o-glycosidic bond and is not available to be reduced, but on the green end it can be reduced since its available and a reducing end

In sucrose on the bottom, both reducing ends (circled in black = anomeric carbon) are involved in o-glycosidic bond meaning that neither can be reduced as they are both occupied

Question 13

Glycogen structure (reducing vs non-reducing ends)

Answer 13

1) One reducing end by glycogen molecule
**Technically not true, because the first glucose is bonded to a protein (glycogenin) so it is not available to be reduced

2) All other ends are called non-reducing end

Question 14

Why are we generating glycogen

Answer 14

One molecule of glycogen displays a third of the osmotic pressure when compared to the number of glucose monomers constituting this glycogen molecule. If glucose molecules were stocked unchanged in the cell, the cell would be highly osmotic, so water would permeate into the cell, and pumping out the excess water would be too costly in energy, the cells would just burst open.
This allows the cell to keep a negative concentration gradient of glucose between the interior and the exterior of the cell, therefore facilitating glucose entry into the cell (trick the cell to think there is no glucose inside but it is in fact glycogen).

Question 15

Why does glycogen have this chain-like shape

Answer 15

These branches allow a greater number of non-reducing ends. These non-reducing ends are the site of glycogen metabolism (catabolism and anabolism), so the more non-reducing ends there are, the quicker the glycogen is metabolized (more efficient for glycogen breakdown because breakdown can be occurring at multiple ends at the same time)

Question 16

Where is glycogen stored

Answer 16

1. The liver
2. The muscle

Question 17

Characteristics of glycogen liver storage

Answer 17

• Glycogen for public usage
  -In case of need (fasting), the liver exports glucose resulting from glycogen breakdown towards other organs (mainly the brain).
  -Liver store = 1/3 of stored glycogen in body = 190 g, 1/8 of liver weight!
  -But liver glycogen reserve can be exhausted in less then 24h!

Question 18

Characteristics of muscle glycogen storage

Answer 18

-glycogen for « privateusage»
-Muscles use glycogen during muscle contractions.
-Muscle stores = 2/3 of stored glycogen in body = 300 g, only 0,8% of total muscle weight.
-But muscle glycogen reserve can be exhausted in 1 to 2h of exercise

Question 19

Where in the liver are we storing glycogen

Answer 19

Glycosome: like an organelle (glycogen molecule with machinery surrounding it in synthesis and breakdown of glycogen (work together)