DNA and Replication

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Slide 1

DNA and Replication

Slide 2

History of DNA

Slide 3

History of DNA

Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA

Proteins were composed of 20 different amino acids in long polypeptide chains

Slide 4

Transformation

Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria

He found that R strain could become virulent when it took in DNA from heat-killed S strain

Study suggested that DNA was probably the genetic material

Slide 5

Griffith Experiment

Slide 6

History of DNA

Chromosomes are made of both DNA and protein

Experiments on bacteriophage viruses by Hershey & Chase proved that DNA was the cell’s genetic material

Radioactive 32P was injected into bacteria!

Slide 7

Discovery of DNA Structure

Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G)

In a body or somatic cell:

A = 30.3%

T = 30.3%

G = 19.5%

C = 19.9%

Slide 8

Chargaff’s Rule

Adenine must pair with Thymine

Guanine must pair with Cytosine

The bases form weak hydrogen bonds

Slide 9

DNA Structure

Rosalind Franklin took diffraction x-ray photographs of DNA crystals

In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

Slide 10

Rosalind Franklin

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DNA Structure

Slide 12

DNA

Two strands coiled called a double helix

Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds

Center made of nitrogen bases bonded together by weak hydrogen bonds

Slide 13

DNA Double Helix

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