POLYSACCHARIDES From Greek:

Poly meaning manySacchar meaning sugarAre made from sugars

Polysaccharides

Figure 3.13

(a) Starch

Starch granules inpotato tuber cells

Glucosemonomer

(b) Glycogen

GlycogenGranulesIn muscletissue

(c) Cellulose

Cellulose molecules

Cellulose fibril ina plant cell wall

One familiar example of a polysaccharide is starch

– Plant cells store starch for energy

– Potatoes and grains are major sources of starch in the human diet

Animals store excess sugar in the form of a polysaccharide called glycogen

• Glycogen is similar in structure to starch

Cellulose is the most abundant organic compound on Earth

– It forms cable-like fibrils in the tough walls that enclose plants

– It is a major component of wood

– It is also known as dietary fiber

Most animals cannot derive nutrition from fiber

– How do grazing animals survive on a diet of cellulose?

– They have bacteria in their digestive tracts that can break down cellulose

5. Small differences in structure can cause major differences in the behaviour and shape of the sugar

Galactose and glucose are optical isomers (same number and types of atoms, different properties).

Galactose is not very water-soluble therefore is not easily absorbed – is not digested

Key Characteristics of Sugars

1. They are hydrocarbons with carbonyl groups (C=O) and multiple hydroxyl groups (OH)

2. Carbon skeletons are 3 to 7 carbons long.

3. Their names end in the suffix “ose”.

Ketose vs Aldose4. If the carbonyl group is in the middle of

the chain it is classified as a ketose, and if it is on the end of a chain as an aldose.

Naming sugars:1. Prefixes of: Mono, di, tri, … poly

Mono is a single sugarDi = two sugars joinedTri = three sugars joinedPoly = many sugars joined

2. Depending on the size of a carbon skeleton (ranges from 3 – 7), monosaccharides are named as:

Trios – 3 carbon chainTetrose – 4 carbon chainPentose – 5 carbon chainHexose – 6 carbon chainHeptose – 7 carbon chain

3. Aldose vs. Ketose (See earlier notes)

Forming name: (keto-/aldo-) + (# of carbons) + -ose

Examples

a monosaccharide that contains an aldehyde and three carbons is formed in this way:

aldo- + tri + ose ------> aldotriose

a five carbon sugar that contains a ketone is called a ketopentose.

TASKWorksheet questions 1 - 9