Biology 1001A Chapter Notes - Chapter Cycle 2: Erwin Chargaff, Dna Replication, Nitrogenous Base
Document Summary
Section 12. 2: dna replication is bi-directional, semi-conservative, semi-discontinuous. 12. 2a dna consists of four nucleotides; each nucleotide has a five-carbon sugar (deoxyribose), a phosphate group, and an nitrogenous base (either adenine, guanine, thymine, and cytosine). Adenine and guanine are purines, which are nitrogenous bases built from a pair of fused rings of carbon and nitrogen atoms (ie. double-ring structures) Thymine and cytosine are pyrimidines, which are built from a single carbon ring (ie. single-ring structures) Erwin chargaff, measured the amounts of nitrogenous bases in dna and discovered that they occur in definite ratios. The polynucleotide chain of dna has polarity, or directionality. 12. 3a matthew meselson and franklin stahl has showed that dna replication is semi- conservative. They used a nonradioactive heavy nitrogen isotope to tag the parental dna.