L10 - Glycogen, ribose, and other sugars

Question 1

Pentose phosphate pathway: what is it, how much of glucose catabolism is it responsible for, when is it active, what is it used for, and how is it regulated?

Answer 1

Alternate pathway of glucose catabolism

5-50% of all glucose catabolism (generally <10%)

• High contribution in specific cells
• Active cell division (eg tumour cells)
• Active fatty acid synthesis (eg adipose)

NADPH production - used for biosynthetic pathways
Ribose production - used for nucleotides and supporting DNA/RNA synthesis

Regulation:

Amount G6PDH and 6PGDH protein decreased in starvation

Transcription of both genes - activated by insulin (SREBP-1c)

• inhibited by glucagon (CREB)

Question 2

Glycogen synthesis

Answer 2

Glycogenin

Glycogenin + UDP-glucose -> glycogenin-glucose

Glycogen-glucose + UDP-glucose -> Glycogen-[glucose]6-8

Glycogen-[glucose]6-8 + UDP-glucose -> Glyocgenin-glucose]x

Glyocgenin-[glucose]x + branchin enzyme -> branched Glycogenin

Branched glycogenin + GS + BE +UDP-glucose -> Glycogen

Question 3

Breakdown of glycogen

Question 4

Glycogen: structural features

Answer 4

Brached complex glycogen molecule:
* Visible (30nm diameter), spherical shape
* 60,000 glucose units
* Beta particle

In the liver, 20-30 beta particles associate to form alpha particles

Short term reserve in muscle
Liver reserve is used for starvation

Question 5

Glycogen synthase

Answer 5

GS1 - muscle, etc
GS2 - liver

GSa - active, reg by PKA, AMPK, GSK3, etc
GSb(/I) - inactive, reg by G6P, insulin

Question 6

Glycogen phosphorylase

Answer 6

GPa - active, reg by GPK, AMP, cAMP, etc
GPb(/I) - inactive, reg by G6P, insulin

Question 7

Latency coordination after insulin taken in: what is it and whta is it used for

Answer 7

Glycogen phosphrylase - early

Glycogen synthase - once GP is done

Question 8

Exact

Answer 8

Exact lipids of x length/size wanted/required by cell must be synthesised - glucose will be used