DNA The mechanism

DNA and inheritance Could predict patterns (Mendel) Did not know why Knew Chromosomes played some role Knew protein and nucleic acid located on chromosome Did not know which was most important

Griffith (1928) Used pneumonia to show passing on of genetic material 2 forms of pneumonia he used Smooth and Rough Smooth strain kills Rough strain no affect Varied types of strain given to mice to measure effect

Griffith Results

Conclusions 1) This guy had too much time on his hands 2) He was incredibly bright 3) A nonliving component of a cell could be expressed in another living cell 4) Something in a cell governs how it behaves/lives

Avery (1944) 1 st to identify the substance that causes this transformation Isolated the macromolecules in a killed S cell (centrifuge) Exposed live R cells separately

The experiment R cell exposed to S DNA became lethal

Conclusion 1) He was also very bright 2) DNA is in charge of gene expression Results were not widely accepted, too simplistic

Hershey & Chase (1952) Confirm Avery’s findings Used a bacteriophage (Virus that infects bacteria) Bacteriophage: Protein and DNA

Bacteriophage Bacteriophage: Protein and DNA Cannot replicate themselves Depend upon host bacteria to replicate them If bacteria starts making viruses, know it’s infected

The experiment One set radioactively labeled Phosphorous ( 32 P) One set radioactively labeled Sulfur ( 35 S) Only DNA has phosphorous Only protein has sulfur

The experiment Inject each set of bacteriophage into a bacteria Wash the virus off Observe bacteria under luminescent light

Results Group 2 Bacteria had radioactivley labeled 32 P Group 1 Bacteria did not have radioactivley labeled 35 S Later viruses had the 32 P as well Bacteria did produce virus

Conclusion DNA is the genetic material More questions than answers Shape of DNA and how it passes genetic information on

Nucleotides (1920s) Subunit of Nucleic Acid 5-carbon sugar, phosphate, & nitrogen base 4 possible nitrogen bases DNA, RNA Adenine Guanine Cytosine Thymine: Uracil

Purine & Pyrimidine Purine Bases Adenine & Guanine Double ringed Pyrimidine Bases Thymine (Uracil) & Cytosine Single ring