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