Carbohydates

Monosaccharides

Hexoses + 6 carbons eg. Glucose, Galactose

C6H12O6

Can form a 6 membered pyranose ring, or

5 membered furan ring, eg. Fructose

Pentoses + 5 carbons eg. Xylose, Arabinose

“Anomeric” carbon in the ring form

Can form the glycosidic bond with another sugar molecule

Glycosidic Bond

Formed between 1 carbon of one sugar ring

& any other carbon with a free hydroxyl group

The 2 rings become linked through an Oxygen

Most common combinations with 3 or 4 carbon

1-3, or 1-4 glycosidic bond

Disaccharides

2 sugar units joined together by a glycosidic linkage

Common disaccharides

Sucrose

Glucose 1-2 fructose

Lactose

Galactose 1-4 glucose

Maltose

Glucose 1-4 glucose

Polysaccharide S tarch

Food = Starch?

What is it?

Where do we find it?

What does it do there?

How is it produced?

Amylose

Relatively short chains

Molecular weight up to 5000 d.p. = ?

Polysaccharide chain length not fixed

Easily soluble in water

Adopts a helical conformation

Two chains can intertwine to form a double helix

Solubility

What determines solubility?

Requires close interaction between solute and solvent, so solute behaves just like a solvent molecule.

Why are large molecules less soluble?

Ordering of solvent molecules around solute incurs a decrease in entropy of the system.

From 2nd law of thermodynamics, the entropy of any spontaneous process must increase