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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…

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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,…

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a hexose sugar and energy source, a component in cellulose in plant cell walls


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 =…

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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…

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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.…

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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…

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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…

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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…

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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…

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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,…


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