Polysaccarides
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Polysaccarides. Starch and Glycogen. Learning Outcomes. Starch. The most abundant storage chemical in plants The single largest provider of energy for the world’s population Properties Compact Insoluble Readily accessible when needed(quickly hydrolysed). Starch.

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Polysaccarides

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Polysaccarides

Starch and Glycogen


Learning Outcomes


Starch

  • The most abundant storage chemical in plants

  • The single largest provider of energy for the world’s population

    Properties

  • Compact

  • Insoluble

  • Readily accessible when needed(quickly hydrolysed)


Starch

  • A mixture of two compounds

    - AMYLOSE

    - AMYLOPECTIN


How is Amylose made?

2 α-glucose molecules bond together

Via a

Condensation reaction

to form a

1,4-Glycosidic bond

to make a

Disaccharide

called

Maltose


C

C

C

C

O

O

C

C

C

C

C

C

C

C

Condensation reaction

OHH

OHH


C

C

C

C

O

O

C

C

C

C

C

C

C

C

Condensation reaction

OH

OH


C

C

C

C

O

O

C

C

C

C

C

C

C

C

Condensation reaction

O

H2O


C

C

C

C

O

O

C

C

C

C

C

C

C

C

Condensation reaction

4

1

O

disaccharide

a1,4glycosidic bond


How is amylose made …

  • The same condensation reaction is repeated over and over again to join thousands of glucose molecules together

    to make

    AMYLOSE


COMPACT COIL

WHY?

BONDS ARE BROUGHT TOGETHER AT A SLIGHT ANGLE when repeated many times, a spiral molecule is made

Inward pointing H bonds stabilise the structure

STRUCTURE OF AMYLOSE


AMYLOPECTIN

  • Branched molecule – 1,6 glycosic bonds every so often cause side chains

  • Molecule is a tightly packed and brush-like

  • Can be broken down more quickly than amylose


Amylose

-glucose

1,4 glycosidic bonds

Spiral structure

Amylopectin

-glucose

1,4 and some 1,6 glycosidic bonds

Branched structure

Starch Insoluble store of glucose in plantsformed from two glucose polymers:


GLYCOGEN

  • Major storage carbohydrate in animals

  • Large molecule made of α-glucose units

  • Can be broken down to release the glucose

  • Like amylopectin in structure has many more branches though

  • More compact than starch

  • Stored in liver and muscle cells


Structure of Glycogen


Structure linked to function

Both glycogen and starch….

  • Are insoluble – will not bring about large movement of water by osmosis

  • Compact – lots stored in a small space

  • Easily broken down/hydrolysed at the ‘ends’ of the chains – to release glucose for respiration


Questions

  • Glycogen is more branched than amylopectin. Explain how this difference is important to animals

  • Why are glycogen and starch storage molecules whereas glucose is an energy source?


Answers

  • Animals have a higher /rapid demand for energy to support movement of muscles. Increased branching in glycogen means more ‘ends’ to release more glucose for respiration

  • Glycogen and starch must be broken down first before the glucose can be respired. Glucose can be respired immediately.


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