Experiment No.-4:
Experiments establishing
Nucleic acid as Genetic Material

Griffith’s Experiment:
Frederick Griffith (1928)
Finding: Living R strain has been transformed into S strain ( transformation ) by an
unknown substance.
Griffith used two strains of Pneumococcus bacteria, type III-S and type II-R.

Avery’s experiment (1944)
Oswald Avery, Colin MacLeod, and Maclyn McCarty

Finding: DNA is the substance that causes bacterial transformation
Avery’s experiment (1944)
Oswald Avery, Colin MacLeod, and Maclyn McCarty

Hershey and Chase Experiment (1952)
Alfred D. Hershey and Martha Chase
Bacteriophages (T2) produced within bacteria growing in radioactive culture medium
will themselves be radioactive. If radioactive sulfur atoms (35S) are present, they will
be incorporated into the protein coats of the bacteriophages since two of the amino
acids – Cysteine and Methionine contain sulfur. If radioactive phosphorus (32P) is used
instead, the DNA become radioactive — because of its many phosphorus atoms — but
not the proteins.

Finding: This result reinforced the notion that DNA (and not the protein) is the
genetic material.
Hershey and Chase Experiment (1952)
Alfred D. Hershey and Martha Chase

Two RNA-containing viruses were used in this experiment: tobacco mosaic virus (TMV), which infects
the leaves of tobacco leaves, and Holmes ribgrass virus (HRV), which infects grass. The protein can be
separated from the RNA by a simple chemical treatment. When this is done, the isolated RNA is
infective, while the protein is not, suggesting that RNA is the hereditary material of these viruses.
Fraenkel-Conrat Experiment (1957)
H. Fraenkel Conrat and R.Williams

Meselson & Stahl’s Experiment (1952)
Matthew Meselson & Frank Stahl
Proposed by Watson and Crick
Proposed by Max Delbrück

Meselson & Stahl’s Experiment (1952)
Matthew Meselson & Frank Stahl

Spots for Experiment no. 7:
Study of structures of : tRNA (2D and
3D); Prokaryotic RNA polymerase, and
Eukaryotic RNA polymerase II through
photographs

Structure of tRNA (2D and 3D)

Prokaryotic RNA Polymerase

Eukaryotic RNA Polymerase-II