BIOL1003 Lecture Notes - Lecture 1: Maurice Wilkins, Nitrogenous Base, Pyrimidine
BIOL1003: Module 3 – Molecular Genetics
Lecture 1 – Introduction to Molecular Genetics
• Proteins and nucleic acids in cells
• Viruses
o No nucleus
o No membrane
o No "cell"
o Protein capsule
o Nucleic acid inside
• Bacteria
o Cell surrounded by membrane and capsule
o No nucleus - nucleic acids in cell
o Proteins in membranes and capsule
o There is a more dense section in the middle, but the chromomids
o Eukaryotes
• Griffiths experiment
o Put bacteria into mice and the mice died - this was actually a big deal - one cell can
kill another organism
o Another version of this bacterium - without the hardened shell - ice did’t care
o But a mix of the dead hard shelled S cells and the non-shelled R cells the mouse died
• Avery, MacLeod and McCarty's experiment
o Aimed to identify transforming principle
o Grew large patched of S-strain bacteria and tested which different cellular
components was responsible for transformation
o The nucleic acids must be responsible - DNA is the transforming principle
o Not believed so had to be further proved with a viral experiment
• Bacteriophage (bacteria infecting virus)
o Sulfur found in all proteins (starting amino acid)
• How id genetic information expressed as traits
o Nitrogenous bases
• Purines - 6 carbon ring and a 5 membered ring (A, G)
• Pyrimidines - 6 carbon rings (C, T)
o Purines = pyrimidines in DNA
• Watson and Crick
o Used X-ray data from Rosalind Franklin (Maurice Wilkins and Raymond goslings)
o Knowledge of chemical composition of DNA
o Built models
o Had no real evidence for the structure
• Nucleotides
o The monomer building DNA = nucleotide
o Nucleotide monophosphate
o Phosphate, sugar (pentose), nitrogenous base
o The sugar-phosphate backbone I the same along the length of the molecule
o H-bonds
• Weak bonds
• Important structures of biological molecules
• Occur between an electronegative atom (often oxygen or nitrogen) and a
hydrogen atom
• Information is coded into the order of bases
• Adenine - thymine: 2 H-bonds
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