BIOL 2107 Lecture 6: DNA Structure, Recombination and Replication

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How was dna discovered: meischer extracted nuclein (nuclear material) from nuclei of human white blood cells. Chemical analysis of nuclein revealed that its major component was deoxyribonucleic acid (dna). Staining of cells revealed that dna was localized almost exclusively within the chrommosomes. Dna contains four kinds of nucleotides linked in a long chain. Proof that genes are composed of dna: bacterial transformation: griffith did experiments with two strains of streptococcus pneumoniae differing in colony morphology and biological activity. The first strain was smooth (s) and was lethal, whereas the second strain was rough (r) and was nonlethal. Injecting r into mice didn"t kill them: when s was heated and the bacteria killed, the mice didn"t die when injected with it, when r was combined with heated s, the mice died. Griffith concluded that cells from r had taken the genes from the dead s, making the r lethal.

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