Dna Replication - History

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four properties necessary for genetic material

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-carries info that codes for the whole organism
-carries info to accurately copy itself
-chemically stable to carry info over generations
-unstable enough to allow for occasional mutations (genetic diversity)

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three things known about proteins in 1928

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-amino acids comprise polypeptide chains, which comprise proteins
-20 amino acids used in all living things
-amino acids linked by condensation/dehydration synthesis

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two things known about DNA in 1928

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-nucleotides linked by condensation/dehydration synthesis
-possible bases: adenine, thymine, guanine, cytosine

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two things known about chromosomes in 1928

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-"genes" are on chromosomes
-chromosomes had been analyzed and found to contain protein and DNA (two candidates for genetic material)

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1865-trait inheritance through alleles

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Mendel

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1869-discovered DNA ("nuclein")

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Miescher

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1900-independently recreate Mendel's work

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deVries, Corren, Tschermak

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1908-laws of population genetics

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Hardy and Weinberg

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1910-named chromosomes and discovered genes (contained the trait-passing capacity)

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Morgan

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1928-first transformation experiments (DNA could be the genetic material)

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Griffith

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1941-one gene codes for one polypeptide chain

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Beadle and Tatum

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1944-first to prove that DNA is the genetic material

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Avery, MacLeod, McCarty

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1950-T=A and C=G

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Chargaff

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1952-second to prove that DNA is the genetic material

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Hershey and Chase

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1953-determined that DNA is a double helix

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Watson, Crick, Wilkins, Franklin

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1958-DNA replicates semi-conservatively

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Meselson and Stahl

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1966-broke the genetic language code

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Nirenberg and Khorana

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altering genes with DNA from an outside source

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transformation

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bacteria that causes pneumonia

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Streptococcus pneumoniae

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characteristics of "S" pneumoniae

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smooth, pathogenic, has a slime coat that covers its recognition glycoproteins

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characteristics of "R" pneumoniae

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rough, non pathogenic, has a deletion mutation that prevents it from having a slime coat

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four arrangements of bacteria in Griffith's transformations and their outcomes

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-living "S" (mouse died)
-living "R" (mouse lived)
-heat-killed "S" (mouse lived)
-heat-killed "S" and living "R" (mouse died)

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what transferred from "S" to "R" pneumoniae to give it a slime coat in Griffith's transformations

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transforming factor

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protease

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destroys proteins, transformed R-->S

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ribonuclease-RNase

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destroys RNA, transformed R-->S

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DNase

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destroys DNA, did not transform R-->S

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suggested by centrifugation of DNA

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high molecular weight

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suggested by electrophoresis of DNA

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large ionic charge

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suggested by spectrophotometry of DNA

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absorbed most strongly at 260 nm

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suggested by chemical analysis of DNA

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1.67 N : 1 P

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Chargaff's rules

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% T = % A
% G = % C

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Levine

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each of the four nitrogenous bases comprised 25% of a strand of DNA

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definition and example of obligate parasites

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viruses--need host cells to mimic life

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viruses that infect bacterial cells

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bacteriophages ("phages")

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phages used in Hershey and Chase's experiments

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T-even

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two parts of a virus

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protein coat (capsid) and nucleic acid

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nucleic acid used in viruses

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can be either single-stranded DNA, double-stranded DNA, or RNA--ring or linear

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how viruses work

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hijack cell's replicating organelles, make new nucleic acids and proteins, assemble new viruses, and burst cell to infect new cells

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relevance of phosphorous to Hershey and Chase's viruses

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-radioactive P32 isotope
-P found on nucleic acids

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relevance of sulfur to Hershey and Chase's viruses

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-radioactive S35 isotope
-S found on protein capsid

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empty protein capsid

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ghost

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results of centrifugation of Hershey and Chase's viruses

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P32 found in bacteria pellet of bacteria infected by viruses--since P32 was known to be on the nucleic acid, proved that nucleic acid (DNA) is genetic material

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three sources of research for Watson and Crick's model of DNA

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Franklin's X-ray crystallography, Wilkins's research, and Chargaff's ratios

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two isotopes of nitrogen that Meselson and Stahl used

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N14 light and N15 heavy

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isotopes of this molecule have densities close to those of DNA

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CsCl

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conservative theory of DNA replication

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double helix of parent stays intact, and a new one is made for daughter cell

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semi-conservative theory of DNA replication

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parent DNA strands separate, and each daughter cell gets one with a new strand

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dispersive theory of DNA replication

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both strands are segmented apart and divided between daughter cells with segments of new strands

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nitrogen in original DNA used by Meselson and Stahl

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heavy nitrogen (N15)

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nitrogen in environment used by Meselson and Stahl

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light nitrogen (N14)