Lecture 2 - Ch 6.1-6.3

deoxyribose sugar, base, and phosphate

Phosophodiester for backbone and hydrogen bonds for nucleotides

F. Meischer (1869) extracted "nuclein" which was DNA
Staining in 1923 showed DNA localized in chromosomes

The ability to change genetic characteristics

Griffith (1928) two different strains of strep - smooth and rough injected into rats
Smooth was severe response and rough was mild/no response
R could be transfromed to S by heat killed S cells

- growing R-form bacteria in medium in the presence of components from dead S forms
- used enzymes that degraded RNA, protein, or polysaccharide which had no effect on the transforming principle, but an enzyme that degrades DNA destroyed activity completely

DNA was the transforming principle

viruses that infect bacteria

Phages labeled with radioactive DNA or protein based on which elements are incorporated into each (phosphorus versus sulfur) were centrifuged out of phageinfected bacteria

Infected bacteriophages with radioactive phosphorus was recovered in host/cell
ones with radioactive sulfur was recovered in ghosts

Phages confirmed DNA was the transforming principle.

Double helix structure

- Strands are antiparallel
- Sugar – phosphate backbone on the outside
- Base pairs in the middle
- Two chains held together by H bonds between A-T and G-C base pairs

forms left-handed helix and has an irregular backbone: observed in vitro but role unkown

sequence of its bases

- unwound DNA during synthesis of DNA or RNA
- DNA binding proteins that regulate gene expression