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Summary Structures and Functions of Biological Molecules
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Summary of the key structures and functions of carbohydrates, Lipids and Proteins
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Structure and Function of Biological MoleculesPolysaccharides
(poly are less soluble in water than mono)
Starch: main storage material in plants, made from a-glucose molecules
o Amylose -unbranched chain, coiled due to the angle of the glycosidic bonds making it
COMPACT = this is good for storage as we can store more in a smaller space
o Amylopectin -branched chain which allows many molecules to be snipped off at once,
this means the process is QUICKER when lots of energy is required.
o Starch is also Insoluble meaning water cannot enter the cells and cause them to swell
which is bad for storage molecules
Glycogen: main storage material for animals as they store excess glucose as glycogen
o Structure is like amylopectin meaning it has branched chains and compact, however,
o Tend to have smaller chains, so less likely to coil and have more side branches than
amylopectin. More branches mean more compact and can be released quicker as
animals require more energy
Cellulose: material for plant cell walls, made of b-glucose molecules
o Micro/macrofibrils have HIGH TENSILE STRENGTH due to glycosidic bonds and hydrogen
bonds between chains
o Macrofibrils run in all directions along the cell wall giving extra strength
o Difficult to digest due to the glycosidic bonds being hard to break and most animals not
having the enzyme to catalyse this reaction
Lipids
Triglycerides: Mainly used as energy storage and a source due to,
o Being INSOLUBLE, they’re not affected by the water potential of the cell as they have a
higher proportion of hydrogen atoms than carbohydrates and almost no oxygen
o LONG HYDROGEN TAILS, contain chemical energy, which is released when broken down
in respiration, because of this lipid are also used as an energy source which release
twice the amount as carbohydrates but produce more water.
Lipids also act as HEAT INSULATION for animals, BUOYANCY as fat is less dense and
PROTECTION around organs as shock absorbers
Phospholipids: make up bilayers of cells membranes and control movement through
Hydrophilic heads form a double layer facing out towards water
Hydrophobic tails in the centre of the bilayer make it hard for water-soluble substances
to pass through, creating a barrier to these substances
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