Ch 5A

• Properties genetic material must possess

  • Able to store information
  • Able to replicate
  • Able to change over time
• Gregor Mendel


  First to describe heredity and transmission of traits from one generation to the next
• Thomas Hunt Morgan


  Determined that traits are associated with chromosomes, which are the heritable material
• Frederick Griffith's experiment


  1. Studied mice infected with different strains of Streptococcus pneumonia

  2. Observed that a substance is passed from dead S cells to live R cells, transforming them into S cells
• Transformation


  Change due to uptake of external DNA by the cell
• Most scientists thought protein would be the heritable material
• Avery, MacLeod, and McCarty's experiment

  1. Removed specific components using enzymes

  2. Observed that transformation cannot occur unless DNA is present, therefore DNA must be the hereditary material
• Hershey and Chase's experiment

  1. Labeled bacteriophage with either 32P (DNA) or 35S (protein)

  2. Found that 32P-labeled viral DNA entered bacterial cells, while 35S-labeled protein did not
• DNA is the hereditary material
• DNA


  • Polymer of nucleotides connected by phosphodiester bonds
  • Contains deoxyribose, nitrogenous bases, and phosphate

  
• Erwin Chargaff


  • Examined the base composition of DNA in a variety of species
  • Observed that the base composition was not random and differed between species
• Chargaff's rules


  A=T, C=G
• Franklin and Wilkins' experiment

  Used X-ray crystallography to study the structure of DNA
• Watson and Crick's model of DNA

  • DNA is a helix made up of two nucleotide strands (double helix)
  • The helix has a fixed width of 2 nm
  • Two strands run antiparallel
  • Sugar and phosphate face out, nitrogenous bases face in
  • Strands held together by H-bonds
  • A pairs with T, C pairs with G