Biological Molecules

• Biological molecules


  • Carbohydrates
  • Lipids
  • Proteins
• Carbohydrates


  Substances with the general formula CX(H2O)Y
• Types of carbohydrates


  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Monosaccharides


  Single sugar units
• Monosaccharides


  • They are sweet
  • They are crystalline solids at room temp.
  • They dissolve in water
  • They have a low Mr
• Monosaccharides


  • Glucose (most common)
  • Fructose
  • Galactose
• Reducing sugars


  All monosaccharides act as reducing sugars
• Benedict's test


  1. Boil monosaccharide with Benedict's solution

  2. Brick red precipitate forms

  3. CuSO4 is reduced from Cu2+ to Cu+
• Monosaccharides


  They are either aldehydes or ketones depending on the position of the carbonyl group
• Monosaccharides by carbon number

  • Trioses (3 carbons)
  • Tetroses (4 carbons)
  • Pentoses (5 carbons)
  • Hexoses (6 carbons)
• Ring structures


  • Pentoses form furanose rings
  • Hexoses form pyranose rings
• Alpha and beta isomers

  In glucose, the hydroxyl group on carbon 1 can be above or below the ring
• Disaccharides


  Two sugar units joined together
• Glycosidic bond


  The bond joining the two sugars when the hydroxyl groups on carbon 1 and 4 react
• Polysaccharides


  Polymers made from many monosaccharides joined together
• Polysaccharides


  • They are large molecules
  • Are insoluble in water
  • Are not sweet
• Starch


  A polymer of glucose used as a food store in plants
• Formation of amylose


  Condensation reactions between α-glucose molecules
• Formation of amylopectin


  Monomers joined by 1,4 and 1,6 glycosidic bonds
• Glycogen


  A polymer of alpha glucose, the form in which energy is stored in animal cells
• Cellulose


  A polymer of beta glucose, every alternate molecule rotated 180°
• Cellulose


  • Up to 10,000 beta glucose units per chain
  • 60-70 chains form microfibrils held together by hydrogen bonds
  • Microfibrils form macrofibrils with high tensile strength
  • Cellulose fibres have high tensile strength, prevent cell bursting, permeable to water and salts
• Lipids


  Either fats or oils, esters of fatty acids and glycerol
• Unsaturated lipids


  Contain double bonds in the fatty acid chains
• Phospholipids


  Formed when glycerol reacts with 2 fatty acids and a phosphate
• Functions of lipids


  • Energy stores, insulation, shock absorbers, buoyancy, metabolic water production
• Lipids yield more ATP per molecule than glucose in respiration
• Amino Acid


  A building block of proteins, composed of amino acids and a side chain (R-group).
• Starch


  A complex carbohydrate in plants, serving as an energy storage molecule through the breakdown and synthesis of glucose.
• Glycogen


  A complex carbohydrate in animals, serving as an energy storage molecule, and is broken down to glucose and subsequently into energy-rich molecules.
• Proteins


  Biomolecules made up of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur
• Monomers of proteins


  Amino acids
• Amino acid structure


  • Contains an amine group (NH2), a carboxylic acid group (COOH), a central carbon, and an R-group
• Specific amino acids


  • Glycine
  • Cysteine
• Formation of peptide bond


  Condensation reaction between amine group and carboxylic acid group, removing H2O
• Peptide bonds connect amino acids in a polypeptide chain
• In addition to peptide bonds, proteins can form other types of bonds: hydrogen bonds, disulfide bonds, ionic bonds, and hydrophobic interactions
• Hydrogen bonds


  Individually weak but can be cumulatively strong when many form, can occur between peptide groups
• Disulfide bonds


  Covalent bonds formed between sulfur atoms in cysteine residues
• Ionic bonds


  Electrostatic attractions between oppositely charged groups