Fig Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells Mouse dies Mouse healthy Living S cells RESULTS EXPERIMENT

Oswald Avery and DNA (1944) Working along with Colin Macleod & Maclyn McCarty Repeated Griffith’s work with modifications Which molecule in the heat-killed was the transformational factor? The components of the Ground up S were isolated, each mixed with R and injected into mice

In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2 To determine the source of genetic material in the phage, they designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection They concluded that the injected DNA of the phage provides the genetic information Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Alfred Hershey and Martha Chase Alfred Hershey and Martha Chase. 1953

Fig Bacterial cell Phage head Tail sheath Tail fiber DNA 100 nm

Fig EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P) Empty protein shell Phage DNA Centrifuge Pellet Pellet (bacterial cells and contents) Radioactivity (phage protein) in liquid Radioactivity (phage DNA) in pellet

Fig (a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA

Erwin Chargaff ( ) and “Chargaff’s Rules” The bases were not present in equal quantities They varied from organism to organism. No matter where DNA came from — yeast, people, or salmon — the number of adenine bases always equaled the number of thymine bases and the number of guanine always equaled the number of cytosine bases. He published a review of his experiments in 1950, calling the ratios — which came to be known as Chargaff’s Rules

Fig. 16-UN1 Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data

GENE MUTATIONS (in DNA)

Point Mutations Happen At Single Nucleotide Points in DNA Substitution – One base changes to (“subs” for) another Insertion – Base added (inserted) Deletion – Base removed (deleted)

The Dog Ate The Fat Cat Substitution – The Dog Ate The Fat Rat Deletion – The Oga Tet Hef Atr At.. Insertion – The Dog Tat Eth Efa Tra t

What kind of point mutation?

What kinds of point mutation?

Insertions and Deletions Can Cause FRAMESHIFTS in the code! Uh Oh! One nucleotide affected every codon down the line—a frameshift!

Mutations may be: Silent or neutral (no effect) Harmful or Fatal (bad effect) Beneficial (good effect, low probability)