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Biological Molecules
Disaccharides
Are formed when two monosaccharides join together in a condensation reaction
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Glycogen and starch are both polymers of alpha=glucose
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Glycogen is more branched
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It is used to form plant cells walls
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The bonds formed are called ester bonds
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The ‘head’ of the phosphate group is soluble in
water (hydrophilic) and the fatty acid ‘tail’ is hydrophobic

Proteins
Amino acids
Proteins are made of amino acids
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They join together by
condensation reaction to form dipeptides
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Add dilute copper II sulfate
Heat sample with Benedict’s reagent
Check no reducing sugars are present
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Hydrolyse the
sample by heating with dilute hydrochloric acid
Neutralise by adding sodium hydrogen carbonate
Test sample with Benedict’s solution
Iodine solution
Dissolve by shaking with ethanol
Pour the resulting solution into water

Positive result
Solution turns
PURPLE from blue
Orange-red
precipitate is formed
Orange-red
precipitate is formed

Turns blue-black
A white emulsion is
formed

Nucleic acids: important information-carrying molecules
Structure of DNA and RNA
DNA
A nucleotide has 3 components:
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A pentose (5-carbon sugar) called
deoxyribose
A phosphate group
A nitrogen-containing organic
base, which can be adenine,
guanine, cytosine or thymine

Two nucleotides join together by a
condensation reaction, forming a
phosphodiester bond
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RNA
Contain 3 nitrogen-containing organic bases adenine, cytosine and guanine but not thymine
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It stays as a single
polynucleotide strand rather than forming a double helix
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RNA transfers genetic information from the DNA in the chromosomes to the ribosomes
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DNA replication
DNA replication is described as semi-conservative because one strand of the old molecule remains intact and a new strand is synthesised
following base pairing rules
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The DNA molecules ‘unzips’
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New DNA nucleotides join on to the exposed template strand of DNA by complementary base-pairing
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We can say the
hydrolysis of ATP is COUPLED to energy-requiring processes in cells
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This reaction is catalysed by the enzyme ATP hydrolase
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This requires an input of energy
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The reaction is catalysed by
the enzyme ATP synthase

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