Zoology

I. Discovery of DNA A. Objectives i. Relate how Griffith’s bacterial experiments showed that a hereditary factor was involved in transformation Ii. Summarize how Avery’s experiments led his group to conclude that DNA is responsible for transformation in bacteria Iii. Describe how Hershey and Chase’s experiments led to the conclusion that DNA, not protein, is the hereditary molecule in viruses

b. Griffith’s Experiments i. 1928, Fredrick Griffith studied Streptococcus pneumonia, which could cause pneumonia Ii., He was trying to develop a vaccine against the disease – causing or virulent, agent Iii. There are two different strains of the disease, one which caused the disease, the S strain, and one which did not, the R strain

iv. His Experiment 1. Inject mouse with live R cells A. Result = mouse lived B. Conclusion = R cells do not kill the mouse 2. Inject mouse with S cells A. Result = mouse died B. Conclusion = S cells kill the mouse

3. Kill S cells with heat and inject the mouse with heat killed S cells A. Result = mouse lived B. Conclusion = heat-killed S cells do not kill mouse 4. Kill S cells with heat and mix with R cells, Inject mouse with mixture A. Result = mouse died B. Conclusion = hereditary material from heat-killed S cells transforms R cells. The transformed R cells kill the mouse.

v. Griffith’s experiments showed that hereditary material can pass from one bacterial cell to another. Vi. The transfer of genetic material from one cell to another cell from one organism to another organism is called transformation.

c. Avery’s Experiment i. In 1940’s Oswald Avery set out to test whether the transforming agent in Griffith’s experiment was protein, RNA, or DNA Ii. Avery’s work showed that DNA is the hereditary material that transfers information between bacterial cells.

d. Hershey-Chase Experiment i. In 1952, Martha Chase and Alfred Avery set out to test whether DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium Ii. Viruses that infect bacteria are called bacteriophages, or just phages

iii. Their Experiment 1. Step 1 – Hershey and Chase used radioactive isotopes to label the protein and DNA in the phage 2. Then they allowed protein labeled and DNA- labeled phage to separately infect E. coli bacteria 3. They removed the phage coats from the cells in a blender

4. They then used a centrifuge to separate the phage from the E. coli 5. They found that all of the viral DNA and little of the protein had entered E. coli cells

Hershey and Chase confirmed that DNA, and not protein, is the hereditary material

II. DNA structure A. Objectives 1. evaluate the contributions of Franklin and Wilkins in helping Watson and Crick discover DNA’s double helix structure 2. describe the three parts of a nucleotide 3. summarize the role of covalent and hydrogen bonds in the structure of DNA 4. relate the role of the base-pairing rules to the structure of DNA

b. DNA Double Helix i. In 1950’s Watson and Crick teamed up to determine the structure of DNA Ii. Proposed that DNA is made of two chains that wrap around each other in shape of a double helix, a shape similar to a winding spiral staircase

Iii. Watson and Crick created a model of DNA by using Franklin and Wilkin’s DNA diffraction X-rays Iv. Received the Nobel Prize in 1962 for their work

c. DNA Nucleotides i. DNA is made of two nucleotide strands that wrap round each other in the shape of a double helix

ii. A DNA nucleotide is made of a: 1. 5-carbon deoxyribose sugar 2. a phosphate group 3. and one of four nitrogenous bases: A. Adenine (A) – purine B. Guanine (G) – purine C. Cytosine ( C ) – pyrimidine D. Thymine (T) – pyrimidine

iii. Bonds hold DNA together 1. DNA double helix is similar to a spiral staircase 2. alternating sugar and phosphate molecules form the side “handrails” of the staircase 3. Nucleotides along each DNA strand are bonded by hydrogen bonds 4. complementary nitrogenous bases are bonded by hydrogen bonds 5. each full turn of the DNA helix has 10 nucleotide pairs

d. Complementary Bases i. In 1949, Chargaff observed the base pairing rules of DNA Ii. Hydrogen bonding between the complementary base pairs 1. G –C 2. A-T 3. Holds t the two strands of a DNA molecule together

iii. Is important because, 1. the hydrogen bonds between the base pairs help the two strands of DNA molecule together 2. The complementary nature of DNA helps explain how DNA replicates before a cell divides – one strand of DNA serves as a template