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Chapter 12 – Molecular Genetics
12.1 DNA: The Genetic Material (Pgs. 326-332)
Frederick Griffith (1928)
Studied 2 strains of the bacteria Streptococcus pneumoniae
Found that one strain could be transformed into the other form
Frederick Griffith
Rough Smooth
Oswald Avery (1944)Took Griffith’s work and discovered
that DNA was the “transforming molecule”
Hershey & Chase (1952)
Provided evidence that DNA was the “transforming factor”
Used bacteriophage (virus that attacks bacteria)
Used radioactive labelingRead pp. 327-328
Bacteriophage
Made of DNA and protein
Inject DNA into host cell
Hershey and Chase
DNA Structure
DNA is a nucleic acid that stores and transmits genetic information.
Polymer made up of nucleotides5-carbon sugar (deoxyribose),
phosphate group,
nitrogen base
DNA Structure
P.A. Levine determined basic structure of nucleotides
Base Groupings
Purines (Double ringed)
1. Adenine (A)
2. Guanine (G)
Pyrimidines (Single ringed)
1. Cytosine (C)
2. Thymine (T)
Backbone of DNA chain formed by sugar and phosphate groups of nucleotides
sugar
phosphate
DNA Structure
Nucleotides bond to form 2 long chains (weak hydrogen bonds) resulting in a ladder like structure called a double helix
DNA found in nucleus
Erwin Chargaff
Discovered that base pairing is the force that holds the two strands of the DNA double-helix together
Chargaff’s Rule C=G and A=T
Rosalind Franklin & Maurice Wilkins
Made x-ray diffraction photographs to study DNA structure
Photo 51
James Watson & Francis Crick
Credited with discovering double helix model of DNA (see figure 12.8, p. 331)
C-G pair by 3 hydrogen bondsA-T pair by 2 hydrogen bondsHypothesized a method of replication
Watson and Crick