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Carbohydrates ­ Cell Biology

What are Carbohydrates?

The most abundant biomolecules on earth
Photosynthesis: >1 x 1011 tons (100 billion tons) of CO2 and H2O into cellulose and other
plant products
Carbohydrate polymers: structural and protective elements in cell walls of bacteria, plants
and animals
Sugars and starch: fuels for…

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Polysaccharides: sugar polymers containing 20 or more monosaccharide units.
e.g. starch, glycogen, cellulose

Carbohydrates Chemically are polyhydroxy aldehydes or ketones

Aldehyde functional group = R ­ COH

Ketone functional group = R ­ CO ­ R', where R/R' = C.

The simplest carbohydrates (only one sugar unit) either aldehydes (aldose)…

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Number of carbons
triose: 3 carbons
tetrose: 4 carbons
Pentose: 5 carbons
hexose: 6 carbons
heptose:7 carbons

Monosaccharides with 5 or more carbon atoms tend to have cyclic structures

The most common naturally occurring sugars are aldohexoses and aldopentoses

Monosaccharide Structure
The 3D structure of the sugar is very important…

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The chiral carbon most distant from the carbonyl carbon (C=O) determines whether the sugar
is D or L. All D sugars have the OH group on the right; L sugars have the OH group on the left.
Most naturally occuring sugars (such as glucose) are D.


Disaccharides consist of…

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Hydroxyl group (­OH) of one cyclic monosaccharide can link with the hydroxyl group of
another to make a chain:

The a1 - 4 linkage shows which carbon atoms in each monosaccharide are linked together.

A C-O-C bond is known as an ETHER bond.

The a or b hydroxyl group on…

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Most carbohydrates found in nature are polysaccharides (also called glycans)
They differ in their recurring monosaccharide units, in the types of bonding and the degree
of branching
Homopolysaccharides: contain only a single monomeric species, e.g. starch, glycogen,
Heteropolysaccharidses: contain different monomeric species, e.g. peptidoglycans
Storage polysaccharides consists of…

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Structural Polysaccharides

Cellulose, chitin, and peptidoglycan form long strands with bonds between adjacent
These strands may then be organized into fibres or layered in sheets to give cells and
organisms great strength and elasticity

Glycoproteins: Cell Identity

Although polysaccharides are unable to store information, they do display information on…

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Breaking the C ­ C bonds and the C ­ OH bonds releases energy that can be "harvested"
into Adenosine TriPhosphate (ATP), the energy currency of the cell.


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