Transcript 2012polysaccharides1..

POLYSACCHARIDES
From Greek:
Poly meaning many
Sacchar meaning sugar
Are made from sugars
 Polysaccharides
Glucose
monomer
Starch granules in
potato tuber cells
(a) Starch
Glycogen
Granules
In muscle
tissue
(b) Glycogen
Cellulose fibril in
a plant cell wall
Cellulose molecules
(c) Cellulose
Figure 3.13
 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
 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 Aldose
4. 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
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Mono is a single sugar
Di = two sugars joined
Tri = three sugars joined
Poly = many sugars joined
2. Depending on the size of a carbon skeleton
(ranges from 3 – 7), monosaccharides are
named as:
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Trios – 3 carbon chain
Tetrose – 4 carbon chain
Pentose – 5 carbon chain
Hexose – 6 carbon chain
Heptose – 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.
TASK
 Worksheet questions 1 - 9