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Bellwork What is DNA? Where is it located?. Discovery of DNA.

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Presentation on theme: "Bellwork What is DNA? Where is it located?. Discovery of DNA."— Presentation transcript:

1 Bellwork What is DNA? Where is it located?

2 Discovery of DNA

3 Target #1- I can describe the experiment conducted by Frederick Griffith Frederick Griffith –A British medical officer –Studied a bacterium called Streptococcus pneumoniae Can cause pneumonia in mammals –He was trying to develop a vaccine against the virulent strain, disease causing strain, of the bacterium

4 Target #1- cont. Each virulent bacterium is surrounded by a capsule made of polysaccharides that protects it from the body’s defense system –S strain: a virulent strain of bacteria that grows into smooth-edged colonies –R strain: a non-virulent strain of bacteria that grows into rough colonies

5 Target #1- cont. Griffith used the two strains of bacteria in a series of 4 experiments –Provide insight about the nature of the hereditary material.

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7 Target #2- I can explain Griffiths conclusions Griffith concluded that heat-killed virulent bacterial cells release a hereditary factor that transfers the disease- causing ability to the live harmless cells –Transformation: the transfer of genetic material from one cell to another cell or from one organism to another organism

8 Target #3- I can describe the experiment conducted by Avery Oswald Avery –An American researcher who wanted to test whether the transforming agent in Griffith’s experiment was protein, RNA, or DNA –Used enzymes to separately destroy each of the three molecules in heat-killed S cells Protease enzyme  killed the protein in the S cells Dnase enzyme  killed the DNA in the S cells Rnase enzyme  killed the RNA in the S cells –Injected mice with each of the three types of heat-killed S cell batches with live R cells

9 Target #4- I can explain the conclusions of the Avery experiment –Conclusions The cells missing protein and RNA were able to transform R cells into S cells and kill the mice Cells missing DNA did not transform R cells into S cells –Mice survived Concluded that DNA is responsible for transformation in bacteria

10 Target #5- I can describe the Hersey-Chase Experiment Hershey-Chase Experiment –Martha Chase & Alfred Hershey –Set out to test whether DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium Viruses that infect a bacterium are known as bacteriophages

11 Target #6- I can state the steps of the Hershey- Chase experiment Step 1: radioactive isotopes were used to label the protein and DNA in the bacteriophages –Sulfur: protein label –Phosphorus: DNA label Step 2: Allowed protein-labeled and DNA-labeled bacteriophages to infect E. Coli bacteria Step 3: removed the bacteriophage coats from the cells in a blender Step 4: used a centrifuge to separate the bacteriophage from the E. Coli Conclusions: found that all of the viral DNA and little of the protein had entered E. Coli cells –DNA is the hereditary molecule in viruses

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13 Hershey-Chase Experiment

14 What is the monomer & polymer of DNA?

15 Ch. 8.2 Structure of DNA

16 Target #7- I can identify the full name for DNA Target #8- I can state what DNA is made of DNA stands for deoxyribonucleic acid The DNA molecule is a long polymer, or chain, of repeating units –The monomers of DNA are called nucleotides –Each nucleotide has 3 parts Phosphate group Deoxyribose sugar Nitrogen base

17 Target #9- I can list the 4 types of nitrogen bases One molecule of human DNA contains billions of nucleotides –4 types of nucleotides, known as nitrogen bases Cytosine (C) Thymine (T) Adenine (A) Guanine (G) – The order of nitrogen bases on a chain of DNA is called a base sequence

18 Target #10- I can differentiate between purines & pyrimidines Purines: a group of nitrogen bases that includes adenine and guanine Pyrimidines: a group of nitrogen bases that includes thymine and cytosine

19 Target #11- I can explain what Chargaff discovered about DNA Erwin Chargaff –Found that the same four bases are found in the DNA of all organisms –The proportion of the four bases differs from organism to organism –Chargaff’s Rule Adenine bonds to Thymine –A  T Cytosine bonds to Guanine –C  G

20 Target #12- I can explain what Rosalind Franklin discovered about DNA Rosalind Franklin –Studied DNA using x-ray crystallography The DNA, when bombarded with x-rays, an image can be captured from the refracted light –X-ray photographs showed an X surrounded by a circle Used later by James Watson & Francis Crick to further develop the shape of DNA

21 Target #13- I can explain what Watson & Crick discovered about DNA James Watson & Francis Crick –One of the many scientists to study proteins and the structure of DNA –Built a model of DNA using wood and metal Found that DNA fits together like a puzzle The base pair combinations discovered by Chargaff were confirmed to be accurate –Double Helix: two strands of DNA wind around each other like a twisted ladder

22 Target #14- I can describe the structure of DNA The DNA nucleotides of a single strand are joined together by covalent bonds –Connect the sugar of one nucleotide to the phosphate of the next nucleotide –The two strands of the helix are held together by hydrogen bonds Chargaff’s rules are more commonly known as base pairing rules –T always pairs with A –C always pairs with G


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