DNAThe Code of Life

Discovery of DNA

Fredrich Mischer

•In 1868, a Swiss physician found a new substance inside of cells and named it nuclein.

•This substance is now known as nucleic acid

The cells he looked at came from the puss of used bandages!

The significance of his discovery remained unknown in Mishcer’s lifetime.

Discovery of DNA

Erwin Chargaff

•In 1950, he found that the number of adenine always equals the amount of thymine and the amount of guanine always equals the amount of cytosine.

•This later became known as Chargaff’s rule.

A=T and C=G provided important clues to figuring out the base pairs of DNA.

Discovery of DNA

Maurice Wilkins

Rosalind Franklin

•In 1952, they used X-ray diffraction to understand the physical structure of the DNA molecule.

•The rays then create complex patterns on photographic film.

This picture provided important clues to figuring out the spiral double helix structure of DNA.

Discovery of DNA

James Watson and Francis Crick

•The structure of DNA was finally realized in 1953.

•Four important findings: 1. The phosphate backbone was on the outside with the bases on the inside2. The molecule was a double helix 3. The two strands run in opposite directions4. Bases have a specific pairing

When they figured out the double helix model , they exclaimed “We have just discovered the secret of life!”

Nobel Peace Prize

In 1962, Watson and Crick shared the Nobel Peace Prize with Maurice Wilkins for the discovery of DNA.

Rosalind Franklin died at the age of 35 in 1958 before the award was given.

Structure of DNA

Phosphate

Deoxyribose (sugar)

Four types of Nitrogen Bases:Adenine = AGuanine = GCytosine = CThymine = T

Alternating sugars and phosphates make up the sides of the ladder. Bases pair up to make the steps of the ladder.

Remember, Chargaff’s Rule! A = T and C = G

Nucleotides•The subunits of DNA

•Made up of one phosphate, one sugar, and one nitrogen base pair

•Base Pairs bond together with weak hydrogen bonds

•Sugar and Phosphate bond together with strong “phosphodieste” bonds

Double Helix Formation= A twisted ladder

Replication of DNA•DNA unzips to form two strands•Free nucleotides create a new strand along the original template strand