Biological molecules

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Most carbohydrates are monomers - large complex molecules composed of long chains of monomers

Monomers - small basic molecular units e.g. monosaccharides, amino acids, nucleotides

Carbohydrates are made from monosaccharides (e.g. glucose, fructose, galactose):

  • contain C, H, O
  • Glucose is a hexose sugar - 6 C atoms
  • 2 types of glucose ( alpha and beta) theyre isomers (same molecular formula - different connection) alpha has OH below H group on right hand side <<see notes>>

Monosaccharides are joined by condensation reactions - glycosidic bond and H20 - a dissacharide is formed             OH HO becomes O and H2O

glucose + fructose = sucrose                              glucose + galactose = lactose

Reverse --> hydrolysis breaks polymers - breaks carbohydrates into monosaccharides  with H2O

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Benedicts test for sugars (e.g. monosaccharides an

Reducing sugars:

  • include all monosaccharides and some disaccharides
  • Add Benedicts reagent (blue) and heat
  • positive will form a coloured precipitate
  • blue green yellow orange brick red
  • -------> higher concentration ------->
  • could filter and weigh

Non Reducing sugars:

  • if reducing is negative could be non reducing
  • have to break into monosaccharides
  • add dilute hydrochloric acid, heat
  • neutralise with sodium hydrocarbonate
  • then carry out Benedicts test
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Polysaccharides - Loads of sugars joied together. 2+ monosaccharides joind together by a condensation reaction. e.g. a-glucose joined by glycosidic bonds to form amylose

Starch - main energy storage material in plants:

  • cells get energy from glucose. Plants store glucose as starch (breaks down when needed)
  • Starch is a mixture of two polysaccharides of alpha glucose:  Amylose (long branched chain, coiled structure, compact so good for storage, fit more into a small space). Amylopectin (long branched chain, side branches allow the enzymes that break down the molecule to get to the glycosidic bonds easily - glucose released quickly)
  • Insoluble - doesnt affect water potential (doesnt cause osmosis into cells) good for storage

Iodine test for starch: Add iodine in potassium solution. Changes from browny orange to blue black

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Glycogen - main storage material in animals:

  • animals store glucose as glycogen (polysaccharide and a-glucose)
  • Structure similar to amylopectin - more side branches - stored glucose can be released quickly
  • compact molecule - good for storage

Cellulose - major component of cell walls in plants:

  • long unbranched chains of beta-glucose
  • beta-glucose molecules' bonds - form straight cellulose chains
  • chains linked by hydrogen bonds to form strong fibres called microfibrils. Structural support.
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(Fats and Oils)      Contain C H O

Used as: Energy store (chemical energy in tails) , Insulation, Protection (kidney), Waterproofing, Buoyancy

Insoluble - because of their tails - doesnt affect water potential of cell and cause water to enter through osmosis

Triglyceride: glycerol and three fatty acid chains (hydrocarbon, hydrophobic tails)

Glycerol's H forms ester bond with OH from carboxyl group in condensation reaction. (hydrolysis reverse)

Fatty acid chains contain carboxyll and r group <<see notes>> Saturated - no double bonds between C atoms. Unsaturated - double bonds between C atoms (monounsaturated - one C=C)

The more C=C, the more unsaturated and so the more bends - cant get as close together so liquid at room temperature

Test by adding ethanol, shaking, adding water. Cloudy white suspension means lipid (emulsion)

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Made from Long chains of amino acids (monomers of proteins - 2 = dipeptide, 3+ = polypeptide) - poteins are made of one or more polypeptide

AA have a carboxyl group (-COOH), an amine group (-NH2) and an R group (variable group)<book>

Polypeptides are formed by condensation reactions - peptide bonds - <see diagram>

on sheet

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