Bellwork

•What is DNA? Where is it located?

Discovery of DNA

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

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

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.

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

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 enzymekilled the protein in the S cells• Dnase enzyme killed the DNA in the S cells• Rnase enzymekilled the RNA in the S cells

– Injected mice with each of the three types of heat-killed S cell batches with live R cells

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

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

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

Hershey-Chase Experiment

What is the monomer &

polymer of DNA?

Ch. 8.2Structure of DNA

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

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

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

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

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

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

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