AMINO ACIDS + PROTEINS + DNA

• Amino acid


  Compound with an amine group and a carboxylic acid group within the molecule
• Amino acids


  • The amine group is always on the second carbon in the chain, so they are always named as '2-amino acids'
  • They are also known as 'α-amino acids'
• Chiral


  The second carbon has four different groups bonded to it, meaning amino acids exist as optical isomers
• In nature, nearly all amino acids exist as a single negative enantiomer so that they 'fit' into the correct cells within living organisms
• Zwitterion


  Amino acids can react as both acids and bases depending on the conditions of the reaction
• Zwitterion formation


  • In acidic conditions (low pH), the lone electron pair is more likely to accept a hydrogen atom, producing a positive (acidic) end to the molecule
  • In basic conditions (high pH), the hydrogen atom on the -OH group is more likely to be lost, producing a negative (basic) end to the molecule
• A zwitterion forms when the overall pH of the molecule is zero, known as the isoelectric point
• Thin-layer chromatography


  Can be used to identify unknown amino acids using UV light to view the traces on the silica plate
• Peptide link


  Bonds that join amino acids together to form proteins
• Hydrolysis


  1. Boiling the protein in 6.0 moldm-3 HCl for 24 hours to reverse the peptide link reaction

  2. In nature, this process is carried out by enzymes so such harsh conditions are not required
• Protein structures


  • Held together with hydrogen bonds, van der waals forces and sulfur-sulfur bonds
• Primary structure


  A single polypeptide chain of amino acids
• Secondary structure


  An α-helix or β-pleated sheet held with hydrogen bonds
• Tertiary structure


  Chains folded into a 3D coil with hydrogen and disulfide bonding
• Disulfide bridge


  Sulfur-sulfur bonds that hold together tertiary structures, keeping the protein structure stable
• Enzyme


  Proteins with a tertiary structure that act as biological catalysts
• Enzymes


  • Contain active sites that are specific to a certain molecule that they break down, called a substrate
  • Enzymes are stereospecific, meaning they can only break down a single enantiomer and will have no effect on the other optical isomer
• DNA (deoxyribonucleic acid)


  A condensation polymer formed from a sugar, a phosphate and a base
• Nucleotide


  Molecules that join together to form DNA, consisting of one sugar, one phosphate and one base
• DNA structure


  • Sugar-phosphate bonds hold together multiple nucleotides into a polynucleotide strand, forming a 'sugar-phosphate backbone'
  • The four possible bases that could be present in the nucleotide are Adenine, Cytosine, Thymine and Guanine
  • These bases pair up to allow a single strand of DNA to join with another via hydrogen bonding to form a double helix structure
• Complementary bases


  • Guanine and Cytosine are complementary bases that bond with three hydrogen bonds
  • Thymine and Adenine are complementary bases that bond with two hydrogen bonds
• Cisplatin


  An anticancer drug that is the cis isomer of a square planar complex of platinum
• Cells in the natural world are chiral so only the Z-isomer of the drug is effective and will be the correct orientation to 'fit' the cells
• Cisplatin has to be able to bond to two adjacent Guanine bases
• Cancer spreads by replicating 'bad DNA'

  Cisplatin bonds to strands of this mutated DNA to prevent it from replicating via ligand replacement with guanine
• Cisplatin can occasionally bond to heated DNA strands causing serious side effects such as hair loss
• To combat these side effects, the drug has to be administered in small amounts
• The long term benefits of using cisplatin and its effectiveness as an anticancer drug means it continues to be used despite the short term side effects