Chapter 12-1:Chapter 12-1: DNA: The DNA: The Genetic MaterialGenetic Material

Section objectives:–Describe the experiments that showed that DNA is the genetic material.

–List the three chemical parts of a DNA molecule.

–Explain the Watson-Crick model of DNA.

–Describe how DNA replicates in a living cell.

History (tab 2)History (tab 2)

• 1869: Friedrch Miescher isolated material from nucleus of fish sperm. Called material nuclein.

HistoryHistory

• 1920’s, scientists found that chromosomes contained DNA.

• While chemical structure of proteins was well understood, DNA was not.–Many believed proteins carried

genetic info.

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HistoryHistory

• 1928: Frederick Griffith found that some factor from harmful, but dead bacteria could transform harmless bacteria into deadly bacteria.

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HistoryHistory

• Many still thought protein carried hereditary info.

• Then came Alfred Hershey and Martha Chase in 1952.

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Their exp’t Their exp’t conclusively conclusively showed DNA showed DNA to be the to be the genetic genetic material (not material (not proteins)proteins)

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The problem then became that of finding what DNA is made of and how it works!

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Composition of DNA (tab 3)Composition of DNA (tab 3)• 5-carbon sugar: deoxyribose5-carbon sugar: deoxyribose• A phosphate groupA phosphate group• 4 kinds of nitrogen-containing bases4 kinds of nitrogen-containing bases

–AdenineAdenine–GuanineGuanine–CytosineCytosine–ThymineThymine

purinespurines

pyrimidinespyrimidines

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Put these together and you have Put these together and you have a a nucleotidenucleotide::

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Structure of DNAStructure of DNA

• James Watson (American James Watson (American biochemist)biochemist)

• Francis Crick (English physicist)Francis Crick (English physicist)

• Used X-ray photos from Rosalind Used X-ray photos from Rosalind Franklin.Franklin.

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(1920 – 1958)

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Shoe Fitting X-Ray Device

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Shoe Fitting X-Ray Device

By 1970 had been banned in 33 states

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DNA Double Helix

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Remember!Remember!

• A pairs with TA pairs with T

• G pairs with CG pairs with C

A-T, G-C

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A and T are made from sticks:

G and C are made from curls:

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Avery and other scientists discovered that • DNA is found in a protein coat.• DNA stores and transmits genetic

information from one generation to the next.

• transformation does not affect bacteria.

• proteins transmit genetic information from one generation to the next.

The Hershey-Chase experiment was based on the fact that

• DNA has both sulfur and phosphorus in its structure.

• protein has both sulfur and phosphorus in its structure.

• both DNA and protein have no phosphorus or sulfur in their structure.

• DNA has only phosphorus, while protein has only sulfur in its structure.

DNA is a long molecule made of monomers called

• nucleotides.

• purines.

• pyrimidines.

• sugars.

Chargaff's rules state that the number of guanine nucleotides must equal the number of

• cytosine nucleotides.

• adenine nucleotides.

• thymine nucleotides.

• thymine plus adenine nucleotides.

In DNA, the following base pairs occur:

• A with C, and G with T.

• A with T, and C with G.

• A with G, and C with T.

• A with T, and C with T.

Quiz (you may use notes)

1.What 3 subunits comprise a nucleotide?2. Whose work with viruses and bacteria

showed that DNA was the genetic material?

3.What 3 scientists discovered the structure of DNA?

4.What 4 nitrogenous bases make up the rungs of the DNA ladder? (you can abbreviate)

AllAbout

Bibliography

History/F

amous P

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DN

A S

tructure

RN

A

How

it all works!