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 dies

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Fig. 16-2Living S cells (control)Living R cells (control)Heat-killed S cells (control)Mixture of heat-killed S cells and living R cellsMouse diesMouse diesMouse healthyMouse healthyLiving S cellsRESULTSEXPERIMENT1Figure 16.2 Can a genetic trait be transferred between different bacterial strains?Oswald Avery and DNA (1944)

Working along with Colin Macleod & Maclyn McCarty

Repeated Griffiths 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

Avery et. al1944In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2To 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 infectionThey 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.1953


Fig. 16-3Bacterial cellPhage headTail sheathTail fiberDNA100 nm5Figure 16.3 Viruses infecting a bacterial cell

Fig. 16-4-3EXPERIMENTPhageDNABacterial cellRadioactive proteinRadioactive DNABatch 1: radioactive sulfur (35S)Batch 2: radioactive phosphorus (32P)Empty protein shellPhage DNACentrifugeCentrifugePelletPellet (bacterial cells and contents)Radioactivity (phage protein) in liquidRadioactivity (phage DNA) in pellet6Figure 16.4 Is protein or DNA the genetic material of phage T2?

Fig. 16-6(a) Rosalind Franklin(b) Franklins X-ray diffraction photograph of DNA7Figure 16.6 Rosalind Franklin and her X-ray diffraction photo of DNAErwin Chargaff (1905-2002)and Chargaffs RulesThe 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 Chargaffs Rules

Fig. 16-UN1Purine + purine: too widePyrimidine + pyrimidine: too narrowPurine + pyrimidine: width consistent with X-ray data10




Point Mutations Happen AtSingle Nucleotide Points in DNASubstitutionOne base changes to (subs for) another

InsertionBase added (inserted)

DeletionBase removed (deleted)The Dog Ate The Fat CatSubstitutionThe Dog Ate The Fat RatDeletionThe Oga Tet Hef Atr At..Insertion The Dog Tat Eth Efa Tra t

What kind of point mutation?

SUBSTITUTIONWhat kinds of point mutation?


INSERTIONInsertions and Deletions Can Cause FRAMESHIFTS in the code!Uh Oh! One nucleotide affected every codon down the linea frameshift!

Mutations may be:Silent or neutral (no effect)

Harmful or Fatal (bad effect)

Beneficial (good effect, low probability)

Chargaffs 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]