DNA, RNA, and Protein Synthesis
Zoology
I. Discovery of DNAA. 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 Experimentsi. 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 Experiment1. Inject mouse with live R cells
A. Result = mouse livedB. Conclusion = R cells do not kill the mouse
2. Inject mouse with S cellsA. Result = mouse diedB. Conclusion = S cells kill the mouse
3. Kill S cells with heat and inject the mouse with heat killed S cellsA. Result = mouse livedB. Conclusion = heat-killed S cells do not kill mouse
4. Kill S cells with heat and mix with R cells, Inject mouse with mixtureA. Result = mouse diedB. 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 Experimenti. 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 Experimenti. 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 Experiment1. 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 structureA. 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 nucleotide3. summarize the role of covalent and
hydrogen bonds in the structure of DNA4. relate the role of the base-pairing rules to
the structure of DNA
b. DNA Double Helixi. In 1950’s Watson and Crick teamed up to
determine the structure of DNAIi. 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 Nucleotidesi. 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 sugar2. a phosphate group3. and one of four nitrogenous bases:
A. Adenine (A) – purineB. Guanine (G) – purineC. Cytosine ( C ) – pyrimidineD. Thymine (T) – pyrimidine
iii. Bonds hold DNA together1. DNA double helix is similar to a spiral
staircase2. 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 Basesi. In 1949, Chargaff observed the base
pairing rules of DNAIi. Hydrogen bonding between the
complementary base pairs1. G –C2. A-T3. Holds tthe 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