Biological Molecules

• All life on Earth shares a common chemistry. This provides indirect evidence for evolution.
• Despite their great variety, the cells of all living organisms contain only a few groups of carbon-based compounds that interact in similar ways.
• Key biological molecules


  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
  • Water
• Monomers


  Smaller units from which larger molecules are made
• Polymers


  Molecules made from a large number of monomers joined together
• Monomers


  • Monosaccharides
  • Amino acids
  • Nucleotides
• Condensation reaction


  Joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
• Hydrolysis reaction


  Breaks a chemical bond between two molecules and involves the use of a water molecule
• Monosaccharides


  The monomers from which larger carbohydrates are made
• Common monosaccharides


  • Glucose
  • Galactose
  • Fructose
• Disaccharides


  Formed by the condensation of two monosaccharides
• Disaccharides


  • Maltose
  • Sucrose
  • Lactose
• Polysaccharides


  Formed by the condensation of many glucose units
• Polysaccharides


  • Glycogen
  • Starch
  • Cellulose
• Glycogen, starch and cellulose


  • Basic structure and functions
• Structure of glycogen, starch and cellulose


  Relationship to function in animal and plant cells
• Triglycerides


  Formed by the condensation of one molecule of glycerol and three molecules of fatty acid
• Phospholipids


  One of the fatty acids of a triglyceride is substituted by a phosphate-containing group
• Triglycerides and phospholipids


  Different properties related to their different structures
• Amino acids


  The monomers from which proteins are made
• Peptide bond


  Formed by a condensation reaction between two amino acids
• Dipeptides


  Formed by the condensation of two amino acids
• Polypeptides

  Formed by the condensation of many amino acids
• Protein structure


  Primary, secondary, tertiary and quaternary
• Protein structure


  Relationship to protein function
• Enzymes


  Proteins that lower the activation energy of the reactions they catalyse
• Properties of enzymes


  • Specificity
  • Effects of factors like enzyme concentration, substrate concentration, inhibitors, pH and temperature on rate of enzyme-controlled reactions
• DNA and RNA are important information-carrying molecules
• DNA nucleotide


  Deoxyribose, phosphate group, one of the organic bases (adenine, cytosine, guanine or thymine)
• RNA nucleotide


  Ribose, phosphate group, one of the organic bases (adenine, cytosine, guanine or uracil)
• DNA molecule


  Double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs
• RNA molecule


  Relatively short polynucleotide chain
• Semi-conservative DNA replication


  1. Unwinding of double helix

  2. Breakage of hydrogen bonds between complementary bases

  3. Role of DNA helicase

  4. Attraction of new DNA nucleotides to exposed bases on template strands and base pairing

  5. Role of DNA polymerase in condensation reaction
• ATP is a nucleotide derivative formed from ribose, adenine and three phosphate groups
• Hydrolysis of ATP


  Catalysed by ATP hydrolase, releases ADP and inorganic phosphate
• Hydrolysis of ATP

  Can be coupled to energy-requiring reactions within cells
• Inorganic phosphate released during ATP hydrolysis


  Can be used to phosphorylate other compounds, often making them more reactive
• Resynthesis of ATP


  Condensation of ADP and inorganic phosphate, catalysed by ATP synthase during photosynthesis or respiration
• Properties of water


  • Metabolite in many reactions
  • Important solvent
  • High heat capacity
  • Large latent heat of vaporisation
  • Strong cohesion between molecules
• Inorganic ions occur in solution in the cytoplasm and body fluids of organisms