Chapter 14

Summary		Questions		Media Resources
14.1 What is the genetic material?
• Eukaryotic cells store hereditary information within the nucleus. • In viruses, bacteria, and eukaryotes, the hereditary information resides in nucleic acids. The transfer of nucleic acids can lead to the transfer of hereditary traits. • When radioactively labeled DNA viruses infect bacteria, the DNA but not the protein coat of the viruses enters the bacterial cells, indicating that the hereditary material is DNA rather than protein.		1.  In Hammerling's experiments on Acetabularia, what happened when a stalk from A. crenulata was grafted to a foot from A. mediterranea? 2.  How did Hershey and Chase determine which component of bacterial viruses contains the viruses' hereditary information?		•DNA is the Genetic Material (Griffith/Hershey/Chase) •Griffith's Experiment of Transformation •Hershey-Chase Experiment
14.2 What is the structure of DNA?
• Chargaff showed that the proportion of adenine in DNA always equals that of thymine, and the proportion of guanine always equals that of cytosine. • DNA has the structure of a double helix, consisting of two chains of nucleotides held together by hydrogen bonds between adenines and thymines, and between guanines and cytosines.		3.  What is the three-dimensional shape of DNA, and how does this shape fit with Chargaff's observations on the proportions of purines and pyrimidines in DNA?		•DNA Structure •Nucleic Acids •DNA Structure *Activity: Three-Dimensional DNA •Isolating DNA Polymerase (Kornberg)
14.3 How does DNA replicate?
• The hereditary message in DNA is replicated with great accuracy through semiconservative replication. • During replication, the DNA duplex is unwound, and two new strands are assembled in opposite directions along the original strands. One strand elongates by the continuous addition of nucleotides to its growing end; the other is constructed by the addition of segments containing 100 to 2000 nucleotides, which are then joined to the end of that strand.		4.  How did Meselson and Stahl show that DNA replication is semiconservative? 5.  How is the leading strand of a DNA duplex replicated? How is the lagging strand replicated? What is the basis for the requirement that the leading and lagging strands be replicated by different mechanisms?		•DNA Replication • DNA Replication •Activity: The Replication Process • Microsatellites in Rabbits ?? • DNA Replication is Semiconservative (Meselson-Stahl ) •DNA Synthesis is Discontinuous (Okazaki) • Base-Pairing
14.4 What is a gene?
• Most hereditary traits reflect the actions of enzymes. • The traits are hereditary because the information necessary to specify the structure of the enzymes is stored within the DNA. • Each enzyme is encoded by a specific region of the DNA called a gene.		6.  What hypothesis did Beadle and Tatum test in their experiments on Neurospora? What did they do to change the DNA in individuals of this organism? How did they determine whether any of these changes affected enzymes in biosynthetic pathways?		• The Future of Molecular Biology ? •Genes Encode Enzymes (Ephrussi/Beadle/Tatum) • One-Gene/One-Polypeptide Evidence

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