Chapter 11 - Chapter 11 DNA and Its Role in Heredity What...

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Chapter 11 DNA and Its Role in Heredity What Is the Evidence that the Gene Is DNA? By the 1920’s, circumstantial evidence pointed to DNA as the genetic material DNA was found in the nucleus and chromosomes were known to carry genes Quantity of DNA varies among species Somatic cells had twice as much DNA as eggs or sperm, as would be expected from Mendel’s discoveries DNA: The Genetic Material In the 1920s, Frederick Griffith performed experiments with two strains of the bacterium Streptococcus pneumoniae . He discovered that a chemical “transforming principle” of dead cells from one strain could cause a heritable change in the other strain Oswald T. Avery and colleagues spent several years identifying the “transforming principle” When DNA was destroyed, the transforming activity was lost, but when DNA was left intact, the transforming activity survived In 1952, Alfred D. Hershey and Martha Chase confirmed DNA is the genetic material T2 bacteriophage (virus that attacks bacteria) consists of DNA core packed in protein coat Genetic transformation of eukaryotic cells was demonstrated – called transfection Uses a genetic marker — a gene that confers an observable phenotype Any cell can be transfected, even an egg cell — results in a transgenic organism What Is the Structure of DNA? The structure of DNA was determined using many lines of evidence In the 1950s, chemists Rosalind Franklin and Maurice Wilkins provided key information about DNA structure using X-ray crystallography A purified substance can be made to form crystals The position of atoms is inferred by the diffraction pattern of X-rays passed through it…recorded on film Chemical composition also provided clues…DNA is a polymer of nucleotides , each comprised of : deoxyribose, a phosphate group, and a nitrogen-containing base DNA nucleotides differ only in their nitrogenous bases : Two purines (adenine and guanine) and two pyrimidines (cytosine and thymine) In 1950, Erwin Chargaff noted that A = T, and G = C Chargaff’s rule – the total abundance of purines = total abundance of pyrimidines in DNA James D. Watson and Francis Crick established the general structure of DNA in 1953 X-ray crystallography convinced them that the DNA molecule was helical, with certain dimensions. Other evidence for two polynucleotide chains running antiparallel to each other Key features of DNA:
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double-stranded helix diameter is uniform the twist is right-handed antiparallel strands – two strands run in different directions Sugar–phosphate backbones of each strand are on outside of helix
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This note was uploaded on 12/03/2010 for the course BSC 2010 taught by Professor Bowes during the Spring '08 term at University of Florida.

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Chapter 11 - Chapter 11 DNA and Its Role in Heredity What...

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