biological molecules

• Role of Water for Animals


  • Required for chemical reactions such as hydrolysis of food molecules
  • Key component for tissue and bodily fluid
  • Regulation of body temperature through sweat
  • Allow blood to transport substances
• Role of Water for Plants


  • Reactant for photosynthesis
  • Provides physical support to the plant in the form of turgor pressure
  • Allow dissolved mineral salts to be transported from roots to other part of plants
  • Allow sugars to be transported from leaves to other parts of the plant
• Carbohydrate


  • Organic molecules made up of carbon, hydrogen and oxygen
  • Formula: CnH2nOn
  • 3 broad types: monosaccharides, disaccharides and polysaccharides

  
• Monosaccharides


  • Smallest unit of carbohydrate
  • Formula: C6H12O6
  • Examples: glucose, fructose, galactose

  
• Disaccharides


  • Two monosaccharides undergo condensation reaction to form a disaccharide, with removal of a water molecule
  • Can be broken down to component monosaccharides by hydrolysis reaction
  • Enzyme is needed for both condensation and hydrolysis reactions
  • Formula: C12H22O11
  • Examples: maltose, sucrose, lactose

  
• Polysaccharides


  • Formed when thousands of glucose molecules linked together in condensation reactions
  • Examples: glycogen, starch, cellulose
  • Functions: storage of carbohydrates in mammals, storage of carbohydrates in plants, cell wall in plant cells

  
• Benedict test


  1. Add Benedict's solution

  2. Shake the mixture

  3. Heat in boiling water bath for 5 minutes

  4. Observe precipitate formation and colour changes
• Iodine test


  1. Place food substance on a white tile

  2. Add 2-3 drops of dilute iodine solution

  
• Fats


  • Made up of carbon, hydrogen and oxygen
  • No fixed formula, ratio of hydrogen to oxygen is much higher than in carbohydrates
  • One fat molecule contains 1 glycerol to 3 fatty acids, joined together via condensation reaction
  • 3 molecules of water needed to breakdown fat into glycerol and fatty acids
• Functions of Fats


  • Storage molecules that can store a large amount of energy
  • Important component of cell membranes and myelin sheath in nerve cells
  • Used to make steroids and certain hormones
  • Stored as adipose tissue for insulation and cushioning
  • Solvent for fat-soluble vitamins
  • Provide buoyancy and heat insulation for aquatic animals
• Ethanol emulsion test


  1. Add ethanol

  2. Shake thoroughly

  3. Add water

  4. Observe white emulsion if fats are present
• Proteins


  • Organic molecules made up of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur
  • Smallest unit is amino acids
  • Amino acids join together to form polypeptides through condensation reaction
  • Proteins are made of one or more polypeptide chains twisted, folded and coiled into a 3D structure
• Biuret test


  1. Add sodium hydroxide solution

  2. Add copper(II) sulfate solution drop by drop

  3. Observe colour change

  
• Enzymes


  • Biological catalysts that speed up chemical reactions by lowering activation energy, without being chemically altered
  • Required in small amounts as they remain unchanged and can be reused
  • Active site has specific shape complementary to substrate
• Lock and key hypothesis


  • Substrate is the "key", enzyme is the "lock"
  • Only complementary substrate can fit into active site
  • Enzyme-substrate complex lowers activation energy
  • Enzyme catalyses reaction, product dissociates and enzyme is free to catalyse another reaction
• At low temperatures


  Enzymes are inactive, rate of reaction is low
• As temperature increases


  Enzyme and substrate gain kinetic energy, collision frequency increases, rate of reaction increases
• At optimum temperature


  Reaction rate is maximum
• As temperature increases beyond optimum

  Enzyme is denatured, rate of reaction decreases
• At extreme high temperatures


  Enzyme is completely denatured, rate of reaction drops to zero
• At optimum pH


  Enzyme activity is highest
• As pH deviates from optimum

  Enzyme activity sharply decreases due to disruption of bonds holding 3D structure
• At extreme pH levels


  Enzyme is completely denatured, rate of reaction drops to zero