Chapter 11 Dna: The Molecule Of Heredity

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Fredrick Griffith's Experiment

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(a) Living R-strain injected into mice. Results: Mice remains healthy. Conclusion: R-strain does not cause pneumonia.

(b) Living S-strain injected into mice. Results: Mice contracts pneumonia and dies. Conclusion: S-strain causes pneumonia.

(c)Heat-Killed S-strain injected into mice. Results: Mouse remains healthy. Conclusion: Heat-Killed S-strain does not cause pneumonia.

(d)Mixture of living R-Strain and heat-killed S-Strain injected into mice. Results: Mouse contract pneumonia and dies. Conclusion: A substance from heat-killed S-strain can transform the harmless R-strain into a deadly S-strain.

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Front 2

Fredrick Griffith

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Griffith worked with two related strands of bacteria which cause pneumonia in mice. He discovered that when harmless live bacteria were mixed with heat-killed disease-causing bacteria and then injected into mice, the mice died. Griffith’s experiment led to to the conclusion that genetic material could be transferred between cells.

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Griffith discovered that bacteria can be transformed from harmless to deadly laid the groundwork for the discovery that genes are composed of DNA.

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Oswald Avery, Colin MacLeod, and Maclyn McCarty

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discovered that the transforming molecule is DNA.

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They isolated DNA from S-strain bacteria, mixed it with live R-strain bacteria, and produced live S-strain bacteria.

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Front 4

Interpreting the results of Griffith's experiment:

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Heating S-strain cells killed them but did not completely destroy their DNA. When killed S-strain bacteria were mixed with living R-strain bacteria, fragments of DNA from the dead S-strain cells entered into some of the R-strain cells and became incorporated into the chromosomes of the R-strain bacteria. If these fragments of DNA contained the genes needed to cause disease, an R-strain cell would be transformed into an S-strain.

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Front 5

Genes are made of

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DNA

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Front 6

Before it divides, a eukaryotic cell_______.

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duplicates its chromosomes and exactly doubles it's DNA content.

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Front 7

Molecular mechanism of Transformation:

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1. bacteria chromosome

2. DNA fragments are transported into bacterium.

3. A DNA fragment is incorporated into the chromosome.

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DNA consists of four small subunits called

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nucleotides

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Front 9

Each nucleotide in DNA has three parts: a phosphate group, a sugar called deoxyribose, and one of four nitrogen-containing bases:

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adenine(A), guanine(G), thymine(T), or cytosine(C).

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Front 10

Erwin Chargaff

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In 1940's, when biochemist Erwin Chargaff of Columbia University analyzed the amounts of four bases in DNA from organisms as diverse as bacteria, sea urchins, fish, and humans, he found a curious consistency.

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Front 11

"Chargraff's" rule

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The DNA of any given species contains equal amounts of adenine and thymine, as well as equal amount of guanine and cytosine.

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Front 12

British Scientist Maurice Wilkins and Rosalind Franklin

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used X-ray diffraction to study the DNA molecule.

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Front 13

X-ray diffraction studies of DNA

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(a)The x formed of dark spots is characteristics of helical molecules, such as DNA. Measurements of various aspects of the pattern indicates the dimensions of DNA helix; for example the distance between dark spots corresponds to the distance between turns of the helix.

(b)Maurice Wilkins and (c)Rosalind Franklin discovered many of the features of DNA by carefully examining such X-ray diffraction patterns.

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Front 14

Certain viruses infect only bacteria and are aptly called

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bacteriophages

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Front 15

Bacteriophages ("bacteria eaters")

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Depends on it's host bacterium for every aspect of it's life cycle.

When it encounters bacterium, it attaches to the bacterial cell wall and injects its genetic material into the bacterium.

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