Biological Molecules

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Biological Molecules
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Making bonds

• All bonds between subunits are formed in the same
  way
• Condensation reaction
• Removal of water H2O

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Breaking bonds

• All bonds between subunits are broken in the same
  way
• Hydrolysis reaction
• Addition of water H2O

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Types of bonds

• Glycosidic bonds found between the
  monosaccharide subunits in disaccharides and poly
  saccharides
• Peptide bonds found between the amino acids
  that join to form dipeptides and polypeptides
• Ester bonds found between glycerol and fatty
  acids

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Carbohydrates

• Monosaccharides reducing sugars
• Disaccharides mainly non-reducing sugars
• Polysaccharides

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Monosaccharides

• Glucose

• Fructose

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Disaccharides

• Maltose is formed from the condensation reaction
  between two glucose molecules

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• Sucrose (a non-reducing sugar) is formed from the
  condensation reaction between a glucose and a
  fructose molecule

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Polysaccharides

• Starch energy storage molecule in plants
• Glycogen energy storage molecule in animals
• Cellulose structural molecule in plants

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Starch

• Starch is a good energy storage molecule
• Starch molecules build up into compact starch
  grains in plant cells

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Starch molecular

• Is made up of long chains of glucose molecules
• Starch molecules can have many branches

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Starch - structure to function

• Because the molecules are branched they can form
  compact, almost spherical storage molecules
• Insoluble in water does not interfere with
  osmosis
• does not interfere with cell metabolism

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Glycogen

• Glycogen is the energy storage molecule in
  animals
• Found mainly in the liver and muscles

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Glycogen structure to function

• Very highly branched
• Compact for storage
• Branches means stored glucose can be released
  quickly

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Cellulose structure to function

• Long unbranched chains of glucose
• Straight chains linked by H bonds
• Form microfibrils strong fibres
• Structural support in plant cell walls

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Lipids

• Lipids are fats oils and waxes
• Made up of C H and O
• Insoluble in water
• Most fats and oils are triglycerides
• Triglycerides composed of one molecule of
  glycerol and three fatty acids

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Triglycerides - structure

• Fatty acids may all be different
• Joined the glycerol molecule by a condensation
  reaction
• Ester bonds
• Fatty acids tails are hydrophobic

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Triglycerides cont.

• Fatty acid tail may be saturated (no double
  CC- bonds) or unsaturated (some double CC-
  bonds)

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Phospholipids

• Phosphate group replaces one of the fatty acids
• Ionised so make the head hydrophilic while tail
  remains hydrophobic
• Important in cell membranes

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Useful lipids

• Medium/long term energy stores
• Insulation
• Buoyancy
• Physical protection
• Waterproofing
• Source of water

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Proteins

• Subunit amino acids
• Peptide bonds between amino acids
• Primary, secondary, tertiary and quaternary
  structure
• Fibrous and globular

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Proteins structure and function

• H bonds hold the secondary structure of proteins
  together
• Tertiary structure held together by weak ionic
  bonds
• Some proteins also contain disulphide bonds
  between certain amino acids

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Globular proteins

• Hydrophilic side chains on outside
• Soluble
• Easily transported in the blood
• Metabolic activities
• All enzymes
• Haemoglobin

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Fibrous proteins

• Insoluble
• Long polypeptide chains
• Chains often tightly coiled
• Structural found in supportive tissues
• Collagen

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Testing for biological molecules

• Reducing sugars
• Non-reducing sugars
• Proteins
• Lipids

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Reducing sugars

• Heat with Benedicts solution
• Positive result produces a coloured precipitate
• Green, yellow, orange, brick red

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Non-reducing sugars

• Heat with Benedicts solution
• Negative result
• Hydrolyse by heating with acid
• Heat again with Benedicts
• Positive result

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Starch

• Add iodine solution
• Positive result gives a blue black colour

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Proteins

• Add to buiret solution
• (sodium hydroxide and copper sulphate)
• Positive result give a lilac, mauve, purple colour

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Lipids

• Add ethanol to the sample
• Shake and then pour the mixture into water
• Positive result gives a white emulsion on the
  surface