2.1 Carbohydrates
Sandringham college pete hamilton
Covalent Bonding involves the sharing
of electrons
This may involve equal sharing or unequal sharing
Carbon atoms can form 4 covalent bonds
All chemical bonds possess energy which
can be released when the bonds are broken
Carbohydrates
• Compounds of :
– Carbon
C
– Hydrogen
H
– Covalent bonds O
able to form 4 covalent bonds
able to form 1 covalent bond
able to form 2 covalent bonds
Fructose
Carbohydrates
• While often drawn as a linear skeleton, in solution carbohydrates often form
hexagonal shaped ring molecules
This can be further abbreviated for your note taking as a simple hexagon
Macromolecules
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Macro = large
Molecules = 2 or more atoms covalently bonded
Usually referred to as polymers - chain like
Made from several repeating subunits
– The repeated subunits are called monomers
– Like links in a chain
Monomers & Polymers
A monomer is a molecule that is able to bond in long chains.
Polymer means many monomers.
Polymers are also known as macromolecules or large-sized molecules.
Here is a monomer:
Here is a polymer:
This linking up of monomers is called polymerization.
Saccharides = sugars
Monosaccharides = single/simple sugars
Disaccharides = double sugar
Polysaccharide = many/complex sugars
Making or Breaking Polymers
• The chemical mechanisms that cells use to make and
break polymers are similar for all classes of
macromolecules.
dehydration synthesis
Making Polymers
• Monomers are connected by
covalent bonds via a
condensation reaction or
dehydration reaction.
– One monomer provides
a hydroxyl group and
the other provides a
hydrogen and together
these form water.
– This process requires
energy and is aided
by enzymes.
Breaking Down Polymers
• The covalent bonds connecting
monomers in a polymer are
disassembled by hydrolysis.
– In hydrolysis as the covalent
bond is broken a hydrogen atom
and hydroxyl group from a split
water molecule attaches where
the covalent bond used to be.
– Hydrolysis reactions
dominate the
digestive process,
guided by specific
enzymes.
Monosaccharides
Monosaccharides: generally have molecular formulas containing
C : H : O in a 1:2:1 ratio.
fructose
C6H12O6.
glucose
C6H12O6.
nb: most names for sugars end in -ose.
Monosaccharides
Monosaccharides are
also classified by the
number of carbons in
the backbone.
• Monosaccharides, particularly glucose, are a major fuel for cellular work.
• They are also building blocks for of other monomers, including those of
amino acids (protein) and fatty acids (lipids).
• While often drawn as a linear skeleton, in
monosaccharides form rings.
aqueous solutions
Monosaccharides
Disaccharides
Sucrose
C12H22O11.
Examples of Disaccharides
Maltose
Formed from 2 glucose molecules, formed in germinating
seeds from the breakdown of starch, providing energy
Sucrose
Formed from 1 glucose and 1 fructose
molecule and is the form in which
carbohydrates are transported in the phloem
in plants
Lactose
Formed from 1 glucose and 1 galactose
molecule, it is an energy source found in
the milk of nearly all mammals
Polysaccharides of sugars have storage
and structural roles
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Polysaccharides are polymers of hundreds to thousands of
monosaccharides joined together
One function of polysaccharides is energy storage
– it is hydrolyzed as needed.
Other polysaccharides serve as building materials for the cell
or whole organism.
Starch:
• is a storage polysaccharide composed entirely of glucose monomers -Long
chain of glucose molecules 200-500 units
• Used as an energy store in plants.
• Not soluble.
• Forms solid grains inside plant cells (often inside chloroplasts).
• The chains coil up into a basic spiral shape making the molecules compact.
• Hydrogen bonds hold the polysaccharide chain in the compact spiral shape.
Glycogen
• The storage polysaccharide in animals (equivalent to starch in plants).
• Found in liver and muscle cells where a store of energy is needed.
• Many fungi also store glycogen.
• Similar in structure to starch - but more branched.
• Forms tiny granules inside cells which are usually associated with smooth
endoplasmic reticulum.
• Each glycogen molecule contains a upto 30,000 glucose units
Glycogen
Cellulose
• Most abundant organic molecule.
• 300-10,000 + glucose units
• It is very slow to decompose.
• 20-40% of the plant cell wall.
• Hydrogen bonding between monosaccharide molecules in the chain gives
strength.
• Hydrogen bonding between cellulose molecules cause bundles called
microfibrils to develop. These are held together in fibres.
• A cell wall will have several layers of fibres running in different directions gives great strength almost equal to steel.
• Provides support in plants and stops plant cells bursting.
• Freely permeable to water and solutes.