Chapter 16

• What does the double-stranded structure of DNA provide?

  A solution for transmitting heritable information
• What are the three main concepts covered in this chapter?

  • DNA as genetic material
  • Structure of DNA
  • DNA replication process
• How does DNA replication allow genetic information to be inherited?

  By copying DNA from parent to daughter cells
• What are the two chemical components of chromosomes?

  DNA and protein
• Why did researchers initially think protein was the genetic material?

  Due to its heterogeneity and specificity of function
• What distinguishes virulent strains of Streptococcus pneumoniae?

  They are pathogenic and cause disease
• What was Griffith's conclusion about the transformation of bacteria?

  Living R bacteria transformed into pathogenic S bacteria
• What is transformation in genetics?

  Change in genotype and phenotype due to DNA uptake
• What did Avery, McCarty, and MacLeod determine as the transforming factor?

  DNA
• How does a bacteriophage destroy a bacterial cell?

  By inserting its DNA and taking over the cell
• How did Hershey and Chase label viral DNA and protein?

  Using radioactive phosphorus and sulfur
• What conclusion did Hershey and Chase draw from their experiment?

  Only DNA enters the E. coli cell
• What are Chargaff’s rules?

  Adenine pairs with thymine, cytosine with guanine
• What are the three components of a nucleotide?

  Nitrogenous base, deoxyribose, phosphate group
• Who built the first molecular model of DNA?

  James Watson and Francis Crick
• What was Rosalind Franklin’s contribution to DNA discovery?

  She x-rayed DNA to reveal its double helix
• How do pyrimidines differ from purines?

  Pyrimidines have one ring, purines have two
• Why does adenine bond only to thymine?

  Purines and pyrimidines can only bind together
• How did Watson and Crick's model explain Chargaff's rules?

  Adenine pairs with thymine, cytosine with guanine
• What does it mean for DNA strands to be antiparallel?

  One strand runs 5' to 3', the other 3' to 5'
• What is the semiconservative model of DNA replication?

  Each new DNA has one old and one new strand
• How did Meselson and Stahl create heavy DNA?

  By using isotopes of nitrogen, 15N and 14N
• What are the origins of replication?


  Sites where DNA replication begins
• What are the key steps in DNA replication?

  1. Unwinding of the double helix
  2. Complementary base pairing
  3. Formation of new strands

  
• What are the levels of chromatin packing in a eukaryotic chromosome?

  • DNA double helix
  • Nucleosomes
  • 30 nm fiber
  • Looped domains
  • Metaphase chromosome
• What is the semiconservative model of DNA replication?

  One old strand and one new strand
• How did Meselson and Stahl create "heavy" DNA?

  By using isotopes of nitrogen, 15N and 14N
• What are the predicted banding patterns after the second bacterial replication in Meselson and Stahl's experiment?

  • One band of heavy DNA
  • One band of intermediate DNA
  • One band of light DNA
  • Matches semiconservative model
• What are origins of replication?

  Sites where chromosomal DNA replication begins
• How is the replication of eukaryotic DNA speeded up?

  By having hundreds or thousands of origins
• Distinguish between leading and lagging strands during DNA replication.

  • Leading strand: synthesized continuously towards fork
  • Lagging strand: synthesized discontinuously with Okazaki fragments
• Why can a new DNA strand only be synthesized in one direction?

  Because DNA polymerases add nucleotides to the 3' end

  
• What are Okazaki fragments?

  Short segments of DNA on the lagging strand
• How are Okazaki fragments joined together?

  By DNA ligase
• What are the functions of the following proteins in DNA replication?

  1. Helicase
  2. Single Strand Binding Proteins (SSB)
  3. Primase
  4. DNA polymerase III
  5. Topoisomerase
  6. DNA ligase
  7. DNA polymerase I
  8. Helicase: untwists and separates strands
  9. SSB: holds DNA strands apart
  10. Primase: synthesizes RNA primer
  11. DNA polymerase III: adds DNA nucleotides
  12. Topoisomerase: relieves strain from unwinding
  13. DNA ligase: joins DNA fragments
  14. DNA polymerase I: replaces RNA primer with DNA
• Which protein is not an enzyme among those listed?

  Single Strand Binding proteins
• What are the roles of DNA polymerase, nuclease, ligase, and repair enzymes in DNA repair?

  • DNA polymerase: elongates new DNA chains
  • Nuclease: cuts and removes damaged DNA
  • Ligase: joins DNA fragments and replaces primers
  • Repair enzymes: proofread and repair DNA
• How are thymine dimers repaired?

  By a nuclease enzyme and DNA polymerase
• What is a thymine dimer?

  Covalent linking between adjacent thymine bases
• What are telomeres and their protective functions?

  • Special nucleotide sequences at chromosome ends
  • Prevent activation of DNA damage monitoring systems
  • Act as a buffer against gene shortening