BIOLOGICAL MOLECULES

• Biological molecules


  Molecules made and used by living organisms e.g. Carbohydrates, Proteins, Lipids, DNA, ATP, Water, Inorganic Ions
• Functions of carbohydrates


  • Energy source (glucose in respiration)
  • Energy store (starch in plants, glycogen in animals)
  • Structure (cellulose in cell wall of plants)
• Monosaccharides


  • Glucose (alpha and beta), galactose, fructose
• Formula for monosaccharides


  C6H12O6 (isomers = same formula but different arrangement)
• Difference between alpha and beta glucose


  On Carbon 1, alpha glucose has a OH group on the bottom and beta glucose has a OH group on the top
• How monosaccharides are joined together


  Condensation reaction (removing water) – between 2 OH groups
• Bond in carbohydrate


  Glycosidic bond (1,4 – between carbon 1 and carbon 4)
• Disaccharides


  • Glucose + glucose = maltose, glucose + galactose = lactose, glucose + fructose = sucrose
• How polymers are separated

  Hydrolysis (add water)
• Polysaccharide


  Many monosaccharides joined by condensation reaction/glycosidic bonds
• Polysaccharides


  • Starch (long chain of alpha glucose), Glycogen (long chain of alpha glucose), Cellulose (long chain of beta glucose)
• Polysaccharides


  • Carbohydrates
  • Made of a long chain of monosaccharides joined by condensation reaction/glycosidic bonds
  • 3 examples: Starch, Glycogen, Cellulose
  • Starch & Glycogen used as Energy Stores (starch in plants, glycogen in animals), they are made out of many alpha glucose which are used for respiration
  • Cellulose used to form Cell Wall in Plants, made out of many beta glucose
• Structure of Starch


  • Made from Amylose and Amylopectin
  • Amylose = long straight chain of alpha-glucose which is coiled
  • Amylopectin = straight chain of alpha-glucose with side branches (1,6-glycosidic bond)
• Structure of Glycogen


  Straight chain of alpha-glucose (1,4-glycosidic bond) with side branches (1,6-glycosidic bond)
• Properties of Starch and Glycogen as energy stores


  • Insoluble = do not affect water potential of the cell, do not diffuse out of the cell
  • Coiled/Branched = compact, more can fit into a cell
  • Branched/Chained = glucose removed from the end
• Structure of Cellulose


  • β-glucose arranged in a straight chain (each alternative β-glucose is rotated 180 degrees) = cellulose straight chain
  • Many cellulose chains are cross linked by hydrogen bonds to form microfibrils
  • Many microfibrils are cross linked to form macrofibrils
  • Forms structure of cell wall
  • Strong material (prevents plant cell from bursting or shrinking)
• Test for starch


  Add iodine, turns blue/black
• Test for reducing sugar

  Heat with Benedicts, turns brick red
• Test for non-reducing sugar


  1. Heat with Benedicts – no change

  2. Add dilute hydrochloric acid (hydrolyses glycosidic bond)

  3. Add sodium hydrogencarbonate (neutralises solution)

  4. Heat with Benedict - turns brick red
• Types of proteins


  • Globular
  • Fibrous
• Globular proteins


  Soluble proteins with a specific 3D shape e.g. enzymes, hormones, antibodies, haemoglobin
• Fibrous proteins


  Strong/insoluble/inflexible material e.g. collagen and keratin
• Building blocks for proteins

  Amino acids
• Structure of amino acid


  Central carbon, carboxyl group to the right (COOH), amine group to the left (NH2), hydrogen above and R group below
• How amino acids differ


  Have different R groups e.g. glycine has a hydrogen in its R group – simplest amino acid
• How amino acids are joined together


  By condensation reaction between the carboxyl group of one and amine group of another, leaves a bond between carbon & nitrogen (called a peptide bond) forming a dipeptide
• Primary, secondary, tertiary, quaternary structure


  • Primary = sequence of AA, polypeptide chain (held by peptide bonds)
  • Secondary = the primary structure (polypeptide chain) coils to form a helix, held by hydrogen bonds
  • Tertiary = secondary structure folds again to form final 3d shape, held together by hydrogen/ionic/disulfide bonds
  • Quaternary = made of more then one polypeptide chain
• Quaternary structure proteins


  • Collagen (3 chains), antibodies (3 chains), haemoglobin (4 chains)
• Structure of collagen


  • Strong material, used to build tendons/ligaments/connective tissues
  • Primary structure mainly made up of glycine (simplest amino acid)
  • Secondary structure forms a tight coil (not much branching due to glycine)
  • Tertiary structure coils again
  • Quaternary structure made from 3 tertiary structures wrapped around each other like rope
  • = a collagen molecule
  • Many of these collagen molecules make the tendons/ligaments/connective tissues
• Test for protein


  Add biuret, turns purple
• Enzyme


  A biological catalyst (substance that speeds up the rate of reaction without being used up – lowers activation energy)
• What makes an enzyme specific

  Has a specific active site shape, only complementary substrates can bind to the active site to form enzyme-substrate complexes
• Lock and Key Model vs Induced Fit Model

  • LK = active site shape is rigid, only exactly complementary substrates can bind to form ES complexes
  • IF = active site changes shape, the substrate binds to the active site – the active site changes shape so the substrate fits exactly forming an ES complex
• Affect of substrate concentration on enzyme activity

  • Increase substrate concentration, increases chance of successful collisions, increase chance of forming an ES complex, increase rate of reaction
  • This continues until all the enzyme's active sites are full/saturated = maximum rate of reaction
• Affect of enzyme concentration on enzyme activity

  • Increase enzyme concentration, increases chance of successful collisions, increase chance of forming an ES complex, increase rate of reaction
  • This continues until all the substrates are used up = maximum rate of reaction
• Affect of temperature on enzyme activity


  • As temperature increases
  • The kinetic energy increases
  • The molecules move faster
  • Increase chance of successful collisions
  • Increase chance of forming ES complex
  • Increase rate of reaction
  • Carries on till optimum
  • After optimum
  • Bonds in tertiary structure break (hydrogen and ionic bonds)
  • Lose active site shape
  • Substrate no longer complementary
  • Can't form ES complexes
  • Enzyme denatured
• Affect of pH on enzyme activity


  If change pH away from optimum, bonds in tertiary structure break, lose active site shape, no longer form ES complex, enzyme denatured
• Competitive vs Non-Competitive Inhibitors


  • Competitive = a substance with a similar shape to the substrate and a complementary shape to the enzyme's active site, binds to the active site, blocking it, preventing ES complexes from forming
  • Non-Competitive = a substance that binds to another site on the enzyme other then the active site, causes the active site to change shape, so less ES complexes can form
• Types of Lipids


  • Triglycerides (fat for energy store, insulation, protection of organs)
  • Phospholipids (to make membranes)
  • Cholesterol (for membrane stability and make hormones)
• Structure of triglyceride


  • Made of 1 glycerol and 3 fatty acids
  • Joined by condensation reaction, ester bonds
  • Bond is COOC
  • There are 2 types of triglycerides: saturated fat and unsaturated fat