DNAHistory,Structure,and

Check out Griffith’s experiment on page 138

• What is up?• Shows how harmless bacteria can

turn deadly.• How? DNA is transferred!

DNA(de-oxy-ribo-nucleic acid)a nucleic acid that stores and transmits the genetic

information from one generation to the next

Big Players in DNA• Chargaff• Rosalind Franklin• Watson and Crick

People knew that DNA was made up of:

•Adenine (A)•Guanine (G)•Cytosine (C)•Thymine (T)

Erwin Chargaff• Discovered that in any

sample of DNA, the amount of A equals the amount of T and the amount of C equals the amount of G.

• This suggested that A binds with T and that C binds with G.

Rosalind Franklin’sX-Ray Crystallography

• Took x-ray photographs of crystallized DNA

• Discovered that the shape of DNA must be a helix, because of the x-ray pattern

• Died of cancer (too many x-rays?)

An example of X-Ray Crystallography

Watson and Crick• Credited for

discovering the structure of DNA in 1953

• Used Chargaff and Franklin’s discoveries along with toy models to discover the structure

A 3-D Model of DNA

NUCLEOTIDESMade up of:• A phosphate group• 5 carbon sugar• Nitrogenous Base

(nitrogen containing)

PURINES•Adenine (A)•Guanine (G)

PYRIMIDINES•Cytosine (C)•Thymine (T)

Base Pairing in DNAA-T C-G

Guanine Nucleotide

Write the complementary DNA strand for each of these DNA

strands:DNA

• GAATTACA• CCAATTAG• ATAGACAG• CCAGTACA

DNA• CTTAATGT• GGTTAATC• TATCTGTC• GGTCATGT

Examples of DNA Replication