chapter 13

• Who introduced the double-helical model for DNA structure?

  James Watson and Francis Crick
• What is DNA known as in biological terms?

  The substance of inheritance
• How is hereditary information encoded in DNA?

  In sequences of A, T, C, and G
• What traits does the DNA program direct the development of?

  Biochemical, anatomical, physiological, and behavioral traits
• What topics will be discussed in this chapter?

  • Structure of DNA and its discovery
  • Cell replication and DNA repair

  
• What was a major challenge to biologists in the early 20th century?

  Identifying the molecules of inheritance
• What did T. H. Morgan's group show about genes?

  Genes are located on chromosomes
• What two components of chromosomes became candidates for genetic material?

  DNA and protein
• How was the role of DNA in heredity first discovered?

  By studying bacteria and their viruses
• What was the key factor in determining the genetic material?

  Choosing appropriate experimental organisms
• Who began the discovery of the genetic role of DNA?

  Frederick Griffith
• What two strains of bacterium did Griffith work with?

  Pathogenic (S) and harmless (R)
• What phenomenon did Griffith discover when mixing strains?

  Transformation
• What does transformation mean in this context?

  Change in genotype and phenotype due to foreign DNA
• What did Griffith conclude about bacteria?

  Bacteria can transfer heritable traits
• Who confirmed that the transforming substance was DNA?

  Oswald Avery, Maclyn McCarty, and Colin MacLeod
• Why were many biologists skeptical about DNA being the genetic material?

  Little was known about DNA
• Why were proteins considered more likely candidates for genetic material?

  They have a great variety of 3-D forms
• What are bacteriophages?

  Viruses that infect bacteria
• What is required for viruses to reproduce?

  They must infect cells and take over machinery
• What did Hershey and Chase demonstrate in 1952?

  DNA is the genetic material of T2 phage
• What was the purpose of Hershey and Chase's experiment?

  To determine the source of genetic material
• What did Hershey and Chase conclude about the injected DNA?

  It provides the genetic information
• What is a polymer of nucleotides?

  DNA
• What did Erwin Chargaff report in 1950?

  DNA composition varies among species
• What do Chargaff's rules state?

  Equal number of A and T, G and C
• If an organism is 30% A, what is the percentage of G?

  20%
• What is the structure of DNA?

  • Double helix
  • Two antiparallel sugar-phosphate backbones
  • Nitrogenous bases paired in the interior

  
• What technique did Wilkins and Franklin use to study DNA?

  X-ray crystallography
• What did Franklin's X-ray images reveal about DNA?

  DNA is helical and has specific dimensions
• What did Watson and Crick deduce from Franklin's images?

  DNA is made of two strands forming a double helix
• What did Watson and Crick initially think about base pairing?

  They thought bases paired like with like
• What did Watson and Crick conclude about base pairing?

  Adenine pairs with thymine, guanine with cytosine

  
• How do Watson and Crick's findings explain Chargaff's rules?

  A = T and G = C in organisms
• How many total hydrogen bonds are in a 100-base-pair DNA molecule with 20% C-G pairs?

  240
• What is the basic principle of DNA replication?

  • Each strand acts as a template
  • Parent molecule unwinds
  • New daughter strands are built

  
• What does the semiconservative model of replication predict?

  Each daughter molecule has one old and one new strand
• How many chromosomes do humans have?

  46 chromosomes
• How many nucleotides are in the human genome?

  Around 6 billion nucleotides
• How long does it take to replicate all human DNA?

  A few hours