BIOLOGY CHAPTER 8 FROM DNA TO PROTEINS SECTION 8.1 ON IDENTIFYING DNA AS THE GENETIC MATERIAL

8.1 Griffith’s Transforming Principle In 1928, Griffith was a British microbiologist who was studying the bacterium that causes pneumonia (streptococcus pneumoniae) Two forms of the bacteria exist– smooth (s) and rough (r) Smooth form is deadly to mice Killed S did not harm mice Rough bacteria did not kill the mice

Transformation When injected with a combination of the live Rough and dead Smooth the mice died Also, live Smooth bacteria were found in the blood of the dead mice. Conclusion: Somehow the non-lethal Rough bacteria had TRANSFORMED into deadly Smooth bacteria. Genetic material from S had gotten into R and transformed it into S

Oswald Avery In 1944, Another scientist named Oswald Avery devised a clever experiment with chemical analysis Avery’s chemical analysis showed that the transforming agent was probably genetic material not protein Scientists were still skeptical

Hershey and Chase confirm DNA as the genetic material A bacteriophage (also called a phage) is a virus that attacks bacteria by injecting its genetic material (DNA) into the bacteria It is DNA surrounded by a protein coat In 1952, Hershey & Chase used phages & radioactive isotopes which only show up in DNA to successfully support their hypothesis

Additional History In the 1950s, Rosalind Franklin (1920-1958), was a British scientist who was doing X-ray diffraction studies on DNA Her coworker Maurice Wilkins showed her work to two other DNA American researchers without her permission Those two – Watson and Cricks – took her work and figured out the structure of DNA – a double helix The three of them got the Nobel Prize and Franklin, who had died in 1957, was not even mentioned

What makes up a nucleotide? Based on this history, the make up of a nucleotide (the monomer for nucleic acids) became known to have : 1. A Phosphate group (PO4) 2. A ring-shaped, 5 carbon sugar called deoxyribose (remember – anything ending in “ose” is a sugar) 3. A nitrogenous base consisting of a single or double ring built around C and N atoms

Chargaff’s Rule The four nitrogenous bases in DNA are: - THYMINE (T) - ADENINE (A) - GUANINE (G) - CYTOSINE (C) CHARGAFF’S RULE of BASE PAIRING states that Adenine always pairs with Thymine; and Guanine always pairs with Cytosine A-T and C-G