12.1 Identifying the Substance of Genes

By observing bacterial transformation, Avery and other scientists discovered that the nucleic acid DNA stores and transmits genetic information from one generation of bacteria to the next.

Hershey and Chase's experiment with bacteriophages confirmed Avery's results, convincing many scientists that DNA was the genetic material found in genes—not just in viruses and bacteria, but in all living cells.

The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell.

• transformation (339)

• bacteriophage (340)

12.2 The Structure of DNA

DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.

The clues in Franklin's X-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA.

The double-helix model explains Chargaff's rule of base pairing and how the two strands of DNA are held together.

• base pairing (348)

12.3 DNA Replication

DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA.

Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied.

In eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.

• replication (350)

• telomere (352)

• DNA polymerase (351)

Think Visually Using the information in this chapter, complete the following concept map about DNA replication:

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