Fig. 16-2

Living S cells (control)

Living R cells (control)

Heat-killed S cells (control)

Mixture of heat-killed S cells and living R cells

Mouse diesMouse dies Mouse healthy 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

Aver

y et

. al

1944

• 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

Fig. 16-3

Bacterial cell

Phage head

Tail sheath

Tail fiber

DNA

100

nm

Fig. 16-4-3

EXPERIMENT

Phage

DNA

Bacterial cell

Radioactive protein

Radioactive DNA

Batch 1: radioactive sulfur (35S)

Batch 2: radioactive phosphorus (32P)

Empty protein shell

Phage DNA

Centrifuge

Centrifuge

Pellet

Pellet (bacterial cells and contents)

Radioactivity (phage protein) in liquid

Radioactivity (phage DNA) in pellet

Fig. 16-6

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

Erwin Chargaff (1905-2002)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

Chargaff’s Rule

• American biochemist discovers that % of G and C bases are almost equal in any sample of DNA.

• The same thing is true for A and T

• [A]=[T] and [G]=[C]

Fig. 16-UN1

Purine + purine: too wide

Pyrimidine + pyrimidine: too narrow

Purine + pyrimidine: width consistent with X-ray data

PCR

CLONING

GENE MUTATIONS(in DNA)

Point Mutations Happen AtSingle 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?

SUBSTITUTION

What kinds of point mutation?

DELETION

INSERTION

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)