Carbohydrateshttp://myrevisionnotesblog.blogspot.com

What should I know?

Monosaccharides are monomers from which larger carbohydrates are made

Condensation reactions occur to form glycosidic bonds

Disaccharides are formed of two glucose molecules

Glucose has two isomers

Polysaccharides are formed from many glucose units

Structure of glycogen, starch and cellulose

Function (and relationship to structure) of glycogen, starch and glucose

That’s a lot…

Monosaccarides

Condensation reaction

Disaccarides

Polysaccarides

Chemical tests

Monosaccarides

Molecule Structure

Glucose

Fructose

Galactose

Condensation Reaction

Definition: A reaction where two molecules join together producing a larger molecule and water

Basically: two monosaccharides join together by two OH groups forming the bond -O- and water

This is the glycosidic bond

Disaccharides

All formed by monosaccharides joining together by condensation reactions

Di = 2

Disaccharide

Monomer 1 Monomer 2 Picture

Maltose Glucose Glucose

Sucrose Glucose Fructose

Lactose Glucose Galactose

Polysaccharides

Formed by condensation reactions between many glucose units

Examples: Starch, glycogen and cellulose

Starch

Main storage molecule in plants

Easily hydrolysed back into glucose as branched (branched type)

Compact so lots can be stored in a small space (helix shaped type)

Insoluble - plant cells contain water so needs to be insoluble to stay as a molecule

Glycogen

Storage molecule in animals (inc. humans)

Very branched

Short branches

Easily hydrolysed

Cellulose

Structural molecule

Creates the cell wall in plant cells

Made from beta glucose molecules

Unbranched so strong

Chemical Tests

Iodine Test

Test for starch

Iodine solution is orange-brown

Changes to blue-black in presence of starch

Benedict’s Test

Test for monosaccharides and reducing disaccharides

Add Benedict's solution and heat in a water bath. Goes brick red if glucose is present

Won’t be positive in sucrose as this isn’t reducing

Thanks and Good Luck!

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