AP Bio: Unit 6- DNA

Morgan showed that genes are located on chromosomes, so _____ became candidates for the genetic material (both parts of chromosomes)

DNA and protein

The genetic role of DNA began with research by Frederick Griffith in 1928, who worked with different strains of bacteria, both _____ and _____

harmless and pathogenic

• when heat-killed pathogenic strain was mixed w/ living cells of harmless strain, some living ___________

• he called it _________, now defined as a change in genotype and phenotype due to uptake of foreign chromosomes

• cells became pathogenic

• transformation

• bacteria can be infected by viruses, or ______________

• a virus is ______ enclosed by a protective protein coat that infects cells and takes over the cell’s metabolic machinery in order to reproduce

• bacteriophages (or phages)

• DNA (or RNA)

• in 1952, Alfred Hershey and Martha Chase showed that DNA is the genetic material of a phage known as T2

• experiment showed ______________________________, enters an E. coli cell during infection

• only the DNA of the phage, not the protein

  CONCLUSION: DNA is genetic material (not proteins)

• in 1950, Erwin Chargaff reported that ____________, so now we have Chargaff’s rules:

• different species have different DNA

  • Base composition of DNA varies between species

  • In any species, the percentages of A and T bases are equal and the percentages of G and C bases are equal

• In 1953, James Watson and Francis Crick were working on DNA structure while Maurice Wilkins and Rosalind Franklin were using ________ to study molecular structure

• X-ray crystallography

• Franklin’s X-ray images of DNA led to observation that DNA was ____

• Photo 51 also suggested that the DNA molecules was made up of 2 strands, forming a ________

• helical

• double helix

• Franklin concluded that there were ________, w/ the ___________

• Watson built a model in which the backbones were ______ (their subunits run in opposite directions)

• 2 outer sugar-phosphate backbones, nitrogenous bases paired in the interior

• antiparallel

• At first, it was thought bases paired like w/ like (A w/ A, G w/ G, etc.), but this model did not result in uniform width

• Instead, pairing a _________ resulted in uniform width consistent w/ X-ray data

• purine w/ pyrimidine

• Found that ______________ and _____________

  • relates to Chargaff’s rules

    • hydrogen bond only by nitrogenous pairs ( . . . )

• adenine (A) paired only w/ Thymine (T), and guanine (G) paired only w/ cytosine (C)