The document summarizes key experiments and discoveries that helped establish DNA as the genetic material: - Griffith's 1928 experiment showed that genetic material could be transferred between bacteria strains. - Avery et al. later identified the transforming factor as DNA. - Hershey and Chase's 1952 experiment provided further evidence that DNA, not protein, carries genetic information within viruses. - Watson and Crick proposed the double helix structure of DNA in 1953, which explained how it could store and replicate genetic information.

1. COMPILED BY SIPHE KAVE

2. In the early 1900, scientists were convinced that
genetic material must be protein
In 1928, Fredrick Griffith, a British medical
officer made observations and inferences using
two strains of pneumococcus bacteria
Each of the two strains had VIRULENCE, the
ability to cause disease, and AVIRULENCE, the
inability to cause pathogenic effects

3. The R-Cell Strain, exhibited avirulence
The S-Cell Strain, exhibited virulence
He carried out an experiment using R-Cells, S-
Cells and heated S-Cells
R-Cells were injected in one mouse and S-Cells, in
another
The mouse injected with R-Cells survived while the
other injected with S-Cells did not.

4. Heated S-Cells and R-Cells were injected into the
same mouse simultaneously
The mouse died
He deduced that the R-Cells must have altered
their genome by accumulating foreign DNA (from
the heated inactive S-Cells) a process called
TRANSFORMATION

5. In 1944, this experiment was further validated by
Oswald T. Avery and his collegues through
identifying Griffith’s transforming factor as DNA
In 1952, geneticists Alfred Hershey and Martha
Chase carried out a series of experiments using T2
Bacteriophages, Radioactive Sulphur &
Phosphorus

6. The building blocks of DNA are NUCLEOTIDES
Each NUCLEOTIDE is made up of a pentose
sugar, phosphate group and a nitrogeneous base
Specific type of sugar referred to as
DEOXYRIBOSE- A five-carbon sugar missing “1
Oxygen molecule”
Nitrogeneous bases found have two categories:
PYRIMIDINES & PURINES

7. Purines: Adenine & Guanine
Pyrimidines: Thymine & Cytosine

9. In 1953, James Watson & Francis Crick proposa
model for structure of DNA
DNA is Double Helical in structure
Consists of two polynucleotide chains alternating
each other on an imaginary axis
In 1953, Rosalind Franklin used X-Ray diffraction,
a method of determining the 3-D structure of a
molecule, in determining the structure of DNA

10. The nucleotides of a DNA DOUBLE HELIX are
linked by covalent bonds to form an alternating
sugar-phosphate backbone.
3’ Carbon bonded to 5’ phosphate of the adjacent
sugar to form a 3’, 5’ Phosphodiester linkage
Resulting in a polymer of indefinate length with
nucleotides linked in any order

11. To maintain its double helical structure,constant
width, PYRIMIDINES bond with PURINES
ADENINETHYMINE
CYTOSINEGUANINE
Because the two strands run in opposite directions,
they are antiparallel to each other, 3’5’
Nitrogeneous bases bond due to H-bonds between
them