AS Biology OCR Biological Molecules Notes

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  • Created on: 19-05-13 14:45
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Biological Molecules
A) Describe how hydrogen bonding occurs between water molecules, and
relate this, and other properties of water, to the roles of water in living
Hydrogen is slightly positive
Oxygen is slightly negative
Polar molecule
Hydrogen bond (covalent bonding)
Properties of water
Solvent ­ solute/solution
Liquid ­ transport medium
Cohesion ­ molecules stick together (surface tension)
Ice ­ lower density (floats), provides insulation, crystal/lattice structure, molecules move
Thermal stability ­ hard to increase temp, many H+ bonds, specific heat capacity
Metabolic ­ reactant in processes (hydrolysis)
B) Describe, with the aid of diagrams, the structure of an amino acid
N-C-C backbone
Amine group (Blue)
Carboxylic group (yellow)
R group (red)

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C) Describe with the aid of diagrams the formation and breakage of
peptide bonds in the synthesis and hydrolysis of dipeptides and
Condensation reaction
Peptide bond forms
Water (H2O) released
Water (H2O) used
Peptide (covalent) bond broken
D) Explain, with the aid of diagrams, the term, primary structure
specific sequence of amino acids
Peptide bonds
E) Explain with the aid of diagrams, the term secondary structure with
reference to hydrogen bonding
When Amino acids coil or fold
Held together by hydrogen bonds…read more

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Coils / folds even further
Hydrogen bonds
Disulphide bridges ­ two molecules
of an amino acid close together, the
sulphur atoms bond together
Ionic interactions - weak attractions
between oppositely charged parts
the molecule
Hydrophilic/Phobic interaction
(Philic outside/Phobic inside ­
G) Explain with the aid of diagrams the term quaternary structure with
reference to the structure of haemoglobin
Multiple polypeptide chains
Inorganic component (Prosthetic group)
Examples ­ insulin, haemoglobin
4 polypeptide sub units
Two are alpha
Two are Beta
Water soluble globular…read more

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I) Compare the structure & function of a structural (collagen) and globular
(haemoglobin) protein
Haemoglobin (globular) Collagen (fibrous)
Soluble in water Insoluble in water
Prosthetic group (Haem) No prosthetic group
Large range of amino acids in primary 35% primary structure is glycine
Many alpha helix structures Many Left-handed helix structures
Globular Fibrous
J) Describe with the aid of diagrams the molecular structure of
alpha-glucose as an example of a monosaccharide carbohydrate
Hexose sugar (6-carbon monosaccharide)
Examples ­ glucose / fructose
K) State…read more

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Alpha (H on top)
Beta (H below)
Glucose + glucose = Maltose
Glucose + fructose = sucrose
L) Describe with the aid of diagrams, the formation and breakage of
glycosidic bonds in the synthesis and hydrolysis of a disaccharide
(maltose) and a polysaccharide (amylose)
Condensation reaction
1-4 Glycosidic bond
Water released
Hydrolysis = breakage (water added = glycosidic bond broken)
M) Compare and contrast the structure and functions of starch (amylose)
and cellulose
N) Describe with the aid of diagrams the structure of glycogen
Starch…read more

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Alpha glucose
Animal store
Unbranched 1-4 (amylose)
Branched 1-6 (amylopectin)
Stored ­ Muscle & Liver
More branched
Shorter 1-4 links
Beta glucose
Long straight chains
Cross link hydrogen bonds
Many micro-fibrils = Macro-fibrils
O) Explain how the structures of
glucose, starch (amylose), glycogen and cellulose molecules relate to
their function in living organisms
Glucose ­ doesn't affect water potential of cell / easily broken off for energy
during respiration
Starch ­ easily broken down to glucose molecules, which may be respired to…read more

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1 glycerol
3 fatty acids
Condensation reaction
Forms ester bonds
Insoluble in water
1 glycerol
2 fatty acids
1 phosphate group
Condensation reaction
Forms ester bonds
Hydrophilic ­ Phosphate head
Hydrophobic ­ fatty acid tails
Q) Explain how the structure of triglycerides, phospholipids and cholesterol
molecules relate to their functions in living organisms
Compact energy store
Insoluble in water ­ doesn't affect cells water potential
Stored as fat ­ thermal insulation
Cell surface membranes
Cell signalling
Strength and stability…read more

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R) Describe how to carry out chemical tests to identity the presence of the
following molecules:
Protein ­ Biuret test
Reducing/Non-Reducing sugars ­ Benedict's test
Starch ­ Iodine solution
Lipids ­ Emulsion test
Add the biuret reagent
Biuret reagent is pale blue
Contains ­ sodium hydroxide + copper sulphate
Reacts with peptide bonds
Colour changes to lilac
Reducing Sugars
All monosaccharide's are reducing sugars
They reacts with other molecules by giving them electrons
Heat the reducing sugar with benedict's solution
Colour change ­ Blue…read more

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Add with ethanol ­ dissolves the lipids
Add to water
If lipids are present ­ white emulsion will form on top layer
S) Describe how the concentration of glucose in a solution may be
determines using a colorimeter
Benedict's test ­ reducing sugars (glucose)
Results in orange/red precipitate
The more the reducing sugar is present , the more precipitate will form
This means more benedict's solution is used
The more copper sulphate is used in the benedict's test, the less light will be blocked…read more


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