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Glycogen Metabolism and Its Regulation in Biochemistry 440, Fall 2008 - Prof. Rachel Klevi, Study notes of Biochemistry

University of Washington (UW) - SeattleBiochemistry
Prof. Rachel Klevit

Information on glycogen, its structure, metabolism, and regulation in the context of biochemistry 440, fall 2008 lecture 20. Topics include the role of glycogen as a short-term glucose storage form, its polymer structure, and the enzymes involved in glycogen breakdown and synthesis. The document also discusses the thermodynamics of glycogen metabolism and glycogen storage diseases.

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Uploaded on 03/18/2009

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Biochemistry 440, Fall, 2008 Lecture 20
1
Glycogen Metabolism
and its regulation
Reading assignment:
Chapter 15.4-15.5: p. 594-604 (605-609 optional)
2
Lecture 20
Glycogen
• Storage form (short-term) of glucose in vertebrates
and many microbes (starch in plants)
• Mainly formed in liver and muscle to provide a
quick source of energy
• Glycogen in liver is a reservoir for other tissues
during fast (brain, muscles)
• polymer of α-D-glucose
pf3
pf4
pf5
pf8
pf9
pfa

Partial preview of the text

Download Glycogen Metabolism and Its Regulation in Biochemistry 440, Fall 2008 - Prof. Rachel Klevi and more Study notes Biochemistry in PDF only on Docsity!

Glycogen Metabolism

and its regulation

Reading assignment:

Chapter 15.4-15.5: p. 594-604 (605-609 optional)

Lecture (^202)

Glycogen

• Storage form (short-term) of glucose in vertebrates

and many microbes (starch in plants)

• Mainly formed in liver and muscle to provide a

quick source of energy

• Glycogen in liver is a reservoir for other tissues

during fast (brain, muscles)

• polymer of α-D-glucose

Lecture (^203)

Structure of Glycogen

O

OH

OH

OH

OH

CH 2 OH

O

OH

OH

OH

OH

CH 2 OH

O

Most linkages in glycogen are α(1 --> 4)

Lecture (^204)

Structure of Glycogen

 1/10 of the linkages are α(1 --> 6).

O

OH

OH

OH

OH

CH 2 OH

O

OH

OH

OH

OH

CH 2 OH

O

H

Glycogen

breakdown

Figure 15-26 (^) ( α Unbranched1->4) polymer

Nonreducing ends

( α 1->4)

Lecture (^208)

O

OH

OH

OH

CH 2 OH

O

OH

OH

CH 2 OH

O O

O

OH

OH

CH 2 OH

O

O

OPO 3 2-

OH

OH

OH

CH 2 OH

Glucose 1P

O

OH

OH

OH

OH

CH 2 OPO 32 -

Glucose 6P

pyruvate

glycolysis

Glycogen breakdown - phosphorolysis

Lecture (^209)

Glycogen Breakdown

 What would be the product if the

α(1--->4) bonds were broken by hydrolysis

(i.e. if the bonds were attacked by H 2 O

instead of Pi)?

 Would this be as effective a use of glycogen

as an energy source?

Lecture (^2010)

O

OH

OH

OH

CH 2 OH

O

OH

OH

CH 2 OH

O O

O

OH

OH

CH 2

O

OH

OH

CH 2 OH

O

OH

OH

CH 2 OH

O O

O

OH

OH

CH 2 OH

O

Glycogen Debranching Enzyme

Lecture (^2013)

Thermodynamics of Glycogen Metabolism

 Glycogenn+1 + Pi --> Glycogenn + G 1-phosphate

 ΔG’^0 of the phosphorylase reaction is

+3.1 kJ/mole.

In the cell, the ratio of [G1P]/[Pi] ranges from

1/30 to 1/100, so this step is exergonic.

(Q < Keq)

==> Glycogen synthesis is NOT the

reverse of glycogen breakdown!

Lecture (^2014)

Comparison of

Breakdown and Synthesis

 Breakdown:

Glycogenn+1 + Pi -> glycogenn + Glucose 1-phosphate

 Synthesis:

 Glucose 1-phosphate + UTP ---> glucose-UDP + PPi

 PPi + H 2 O --> 2 Pi

 Glycogenn + UDP-glucose --> glycogenn+1 + UDP

Lecture (^2015)

Glycogen synthesis

 UDP-glucose is made

 Glucose is transferred from UDP-glucose

to glycogen

-> making (α1-->4) linkages

 α(1-->6) linkages are introduced

-> making branches

Lecture (^2016)

Synthesis of UDP-glucose

 G1P + UTP ---> glucose-UDP + PPi

 ΔG’^0 = ~ 0 kJ/mol

 PPi + H 2 O --> 2Pi

 ΔG’^0 = -25 kJ/mol

Lecture (^2019)

Glycogen Storage Diseases

 9 different types.

 VII: Lack PFK in muscle.

 I: lack of glucose 6-phosphatase, affects

gluconeogenesis and glycogen storage

 III: lack of debranching enzyme.

 IV: lack of branching enzyme.

Lecture (^2020)

Regulation of Glycogen Metabolism

 Phosphorylase is activated by

phosphorylation

-> regulated by hormonal control

 Glycogen synthase is INactivated by

phosphorylation

Figure 15-

Lecture (^2022)

Glycogen phosphorylase in liver

Figure 15-