Ch. 10: DNA, RNA and Protein Synthesis The discovery of DNA

1928: Frederick Griffith Tried to find a vaccine for pneumonia. Studied two strains of Streptococcus pneumoniae, R cells and S cells, by injecting them into mice.

Griffith’s Experiment “S” strain are virulent (causes disease) “R” strain are avirulent Griffith injected mice with strains of live and dead “S” and “R” bacteria.

Griffith’s Data Strepococcus pneumoniae strain Result on mouse: Live S (control) Live R (control) Heat-killed S (control) Heat-killed S & Live R Dies Lives

Griffith’s Conclusion: The Transforming Principle The dead S bacteria transferred an inheritable material to the R strain. (heredity: passing on of traits) As a result, the living R bacteria was transformed into the S strain.

So, what in the bacteria caused them to “transform” from one strain to another? Protein, DNA, or RNA??

1940’s: Oswald Avery’s Experiment Repeated Griffith’s experiments but removed the protein, DNA, or RNA molecules. Observed which molecule was responsible for “transforming” the R bacteria into S.

Avery’s Data Dead S strain with… Result when S strain is mixed with live R strain: Proteins removed DNA removed RNA removed Mouse dies Mouse lives

Avery’s Conclusion: DNA is the hereditary material that transformed R bacteria into S bacteria.

1952: Alfred Hershey and Martha Chase Experiment Studied bacteriophages (viruses that infect bacteria).

Hershey and Chase Experiment 1. Used radioactive tags to identify DNA ( 32 P) and protein ( 35 S) 2. Infected bacteria with the virus. 3. Used blender to remove virus from the surface of the bacteria. 4. Observed what molecule was transferred from the virus into the infected bacteria

Observations Radioactive protein molecules found outside bacteria. Radioactive DNA found inside bacteria

Hershey and Chases’ Conclusion: DNA is the hereditary material that stores the information about building new virus particles.

The race to find DNA’s structure

1950’s: Watson and Crick Discovered that the structure of DNA is a double helix - two chains that wrap around each other.

Rosalind Franklin and Maurice Wilkins Took X-ray diffraction photographs of DNA crystals, which led Watson and Crick to their discovery.

3 parts of DNA 1. Sugar (Deoxyribose) 2. Phosphate group 3. Nitrogenous base

These make up the basic unit of DNA, which is called the ___________. nucleotide

4 Nitrogenous Bases 1. Adenine (A) 2. Guanine (G) 3. Thymine (T) 4. Cytosine (C) Purine 2 rings Pyrimidine 1 ring

The structure of DNA is like a spiral ladder

The backbone of alternating _____ and _________ are like the handrails. sugar phosphate

The__________ ____ are like the rungs/ steps of the ladder. nitrogenous bases

Draw a picture of DNA

Complementary Chains

Complementary base pairing Adenine bonds with ________ Guanine bonds with________ Bonded by ________ ______. The order of the bases is called the ______ _____________. base sequence Thymine Cytosine hydrogen bonds

Practice: Base pairing

EXIT TICKET 1. If one strand of DNA has the following base sequence, what sequence would the complementary strand contain? ATAGCAGCT 2. What are the two components of the DNA backbone (railing of the staircase)? 3. Name at least two scientists that contributed to deriving the structure of DNA.