2.2 Biological Molecules

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2.2 Biological Molecules
Molecular Bonding
Condensation Reactions ­ a reaction that joins two molecules and H2O is removed
Hydrogen Bond ­ A weak interaction between a slightly positively charged atom and a slightly
negatively charged atom e.g. between the bases of DNA, between the O() of one H2 O molecule and
the H(+) of another
Hydrolysis ­ the splitting of a molecule using water
Monomer ­ a small molecule that binds to many other identical molecules to form a polymer

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Polymer ­ a large molecule made up of many repeating units called monomers
Covalent bonds ­ the sharing of electrons between atoms
Type of molecule Monomer Polymer
Carbohydrate (C, H & O) Monosaccharides Polysaccharides
Protein (C, H, O, N & S) Amino Acids Polypeptides proteins
Nucleic Acid (C, O, H, N & P) Nucleotides DNA & RNA
Carbohydrates (saccharides) are molecular
compounds made from just three elements:
carbon, hydrogen and oxygen.
Monosaccharides and disaccharides are
relatively small molecules.…read more

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a pentose sugar, a component of deoxyribonucleic acid
a pentose sugar, a component in ribonucleic acid
Disaccharide Monosaccharides
Maltose = a glucose + a glucose
Sucrose = a glucose + fructose
Lactose = b glucose + a glucose
Cellobiose = b glucose + b glucose
Amylose is found in plants. It is a long chain of alpha glucose molecules and has glyosidic bonds
between carbons 1 ­ 4. It coils into a spiral shape because of its hydrogen bond.…read more

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Amylopectin is also found in plants and is a long chain of alpha glucose molecules and has glyosidic
bonds between carbons 1 ­ 4. It also has branches joining carbons 1 ­ 6. These branches make the
molecule more compact. It can also give more energy at once as the end of each branch can be
snipped of by hydrolysis, whereas in amylose there are only two ends of the chain available. Both
are stored within plant cells as large granules.…read more

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Cellulose is a plant carbohydrate used in cell walls. It is an insoluble fibrous homopolysaccharide
made from long chains of beta glucose. They are straighter than other carbohydrates as the
hydrogen and hydroxyl groups every other glucose molecule are inverted. The chain is strengthened
by hydrogen bonds between the molecules. Hydrogen bonds are also formed between chains.60 ­
70 chains bound together make a microfibril which then bundle together into a macrofibril
containing around 400 microfibrils.…read more

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Triglycerides are made from glycerol and three fatty acids, joined by three ester bonds between the
hydroxyl groups of the glycerol and the carboxyl group of the fatty acids. This is a condensation
reaction as water is produced.
Saturated fats have no C=C bonds in the molecule. Unsaturated fats do have C=C bonds. This makes
unsaturated fatty acid tails bend.
Functions of triglycerides:
Energy source ­ they can be broken down during respiration to produce carbon dioxide and water.…read more

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Energy store ­ triglycerides are insoluble and therefore can be used as a store of energy. Mammals
store fat in adipose cells under their skin and around organs.
Buoyancy ­ lipids are less dense than water so whales and aquatics can
use them to stay afloat.
Insulation ­ adipose tissue can act as an insulator of heat just as lipids in
nerve cells act as electrical insulators
Protection ­ Fat covers delicate organs to act as a shock absorber for our more delicate organs e.g.…read more

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Phospholipids have the same structure as triglycerides except that one of the fatty acid tails is
replaced with a phosphate group.
The phosphate head is hydrophilic (water loving) and the fatty acid tails are hydrophobic (water
They form micelles in water as the tails come together in the centre of a sphere in order to avoid the
They are amphipathic as they have a polar region at their heads and a nonpolar region between the
tails.…read more

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They are fluid as the phospholipids are free to move around within the layer. They will not however,
expose their tails to the water, which gives the bilayer some stability.
The bilayer is selectively permeable, meaning that it is only possible for small and nonpolar
molecules to diffuse into the cell. This helps control what goes in and out of the cell and keeps the
cell functioning properly.
Cholesterol is a steroid alcohol.…read more

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Constituents in cell membranes ­ e.g. sodiumpotassium pump & carrier proteins
Amino Acids
Amino acids are the monomers that make up all proteins. There are 20
that are proteinogenic. They have an amine group, a carboxyl group,
and a variable R group which acts as another chain of the molecule,
different for each amino acid.
R groups vary in size, polarity, charge and interaction with water.
Almost all amino acid names end in ­ine. E.g. cysteine and alanine.
Unless they have acidic R groups e.g.…read more


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