[基因Ⅸ(基因9).本杰

[基因Ⅸ(基因9).本杰

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Genes Are DNA CHAPTER OUTLINE ... Introduction .. DNA Is the Genetic Material of Bacteria - • Bacterial transformation provided the first proof that DNA is the genetic material of bacteria. Genetic properties can be transferred from one bacterial strain to another by extracting DNA from the first strain and adding it to the second strain. DNA Is the Genetic Material of Viruses Phage infection proved that DNA is the genetic material of viruses. When the DNA and protein components of bacterio- phages are labeled with different radioactive isotopes, only the DNA is transmitted to the progeny phages produced by infecting bacteria. DNA Is the Genetic Material of Animal Cells DNA can be used to introduce new genetic features into animal cells or whole animals. • In some viruses, the genetic material is RNA. Polynucleotide Chains Have Nitrogenous Bases Linked to a Sugar-Phosphate Backbone • Anucleoside consists of a purine or pyrimidine base linked to position 1 of a pentose sugar. Positions on the ribose ring are described with a prime (') to distinguish them. The difference between DNA and RNA is in the group at the 2' position of the sugar. DNA has a deoxyribose sugar (2'-H); RNA has a ribose sugar (2'-OH). • A nucleotide consists of a nucleoside linked to a phosphate group on either the 5' or 3' position of the (deoxy)ribose. Successive (deoxy)ribose residues of a polynucleotide chain are joined by a phosphate group between the 3' position of one sugar and the 5' position of the next sugar. One end of the chain (conventionally the left) has a free 5' end and the other end has a free 3' end. • DNA contains the four bases adenine, guanine, cytosine, and thymine; RNA has uracil instead of thymine. DNA Is a Double Helix The B-form of DNA is a double helix consisting of two polynucleotide chains that run antiparallel. The nitrogenous bases of each chain are flat purine or pyrimidine rings that face inward and pair with one another The diameter of the double helix is 20 A, and there is a complete turn every 34 A, with ten base pairs per turn. • The double helix forms a major (wide) groove and a minor (narrow) groove. DNA Replication Is Semiconservative The Meselson-Stahl experiment used density labeling to prove that the single polynucleotide strand is the unit of DNA that is conserved during replication. Each strand of a DNA duplex acts as a template to synthe- size a daughter strand. • The sequences of the daughter strands are determined by complementary base pairing with the separated parental strands. DNA Strands Separate at the Replication Fork Replication of DNA is undertaken by a complex of enzymes that separate the parental strands and synthesize the daughter strands.
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This note was uploaded on 12/29/2010 for the course LS 112 taught by Professor Hu during the Spring '10 term at Zhejiang University.

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[基因Ⅸ(基因9).本杰

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