Chapter 13: DNA and its role

• What is the main topic of Chapter 13?

  DNA and Its Role in Heredity
• What are the key concepts covered in Chapter 13?

  • Function of DNA as genetic material
  • Structure of DNA
  • Semiconservative replication of DNA
  • Repair mechanisms for DNA errors
  • Polymerase chain reaction (PCR) amplifies DNA
• What is the significance of cisplatin in cancer therapy?

  Cisplatin irreversibly cross-links DNA strands and prevents replication.
• What happens to cells when DNA replication is blocked?

  Cells cannot divide, leading to apoptosis.
• In the 1920s, what was known about chromosomes?

  They consisted of DNA and proteins.
• What evidence supported that DNA is the genetic material?

  A new DNA stain showed it was in the right place, varied among species, and present in the right amounts.
• What are the two types of nitrogenous bases in DNA?

  Purines and pyrimidines.
• Name the purines found in DNA.

  Adenine (A) and guanine (G).
• Name the pyrimidines found in DNA.

  Cytosine (C) and thymine (T).
• What is Chargaff’s rule?

  The amount of purines is always equal to the amount of pyrimidines in DNA.
• How does the relative abundance of A + T versus G + C vary?

  It varies among species.
• What technique was used to reveal the structure of DNA?

  1. ray diffraction.
• Who prepared crystallographs from DNA samples?

  Rosalind Franklin.
• What did Rosalind Franklin's images suggest about DNA?

  DNA has a double-stranded helix with 10 nucleotides in each full turn.
• What did Crick and Watson's model of DNA satisfy?

  Chargaff’s rule by pairing purines with pyrimidines.
• What are the key features of DNA structure?

  It is a double-stranded helix, right-handed, antiparallel, and held together by complementary base pairing.
• How are the sugar-phosphate backbones arranged in DNA?

  They form a coil around the outside of the helix with nitrogenous bases pointing toward the center.
• What holds the two strands of the DNA helix together?

  Hydrogen bonds between complementary base pairs.
• What determines the direction of DNA strands?

  The direction is determined by sugar-phosphate bonds.
• What is the role of DNA polymerase in replication?

  It adds nucleotides to the 3′ end of the growing DNA strand.
• What are the three steps in DNA replication?

  Initiation, elongation, and termination.
• What happens during the initiation step of DNA replication?

  The double helix is unwound, creating two template strands.
• What occurs during the elongation step of DNA replication?

  Complementary base pairs are added and linked by phosphodiester bonds.
• What marks the end of DNA synthesis during termination?

  All DNA regions have been replicated.
• What is the role of the pre-replication complex in DNA replication?

  It binds to the origin of replication to initiate the process.
• How does DNA polymerase require a primer?

  A short starter strand, usually RNA, is needed for DNA polymerase to add nucleotides.
• What is the function of DNA helicase during replication?

  It unwinds the DNA using energy from ATP hydrolysis.
• How do leading and lagging strands differ during replication?

  The leading strand grows continuously, while the lagging strand forms in small, discontinuous stretches called Okazaki fragments.
• What are Okazaki fragments?

  Small, discontinuous stretches of DNA synthesized on the lagging strand.
• What happens to the primer after the lagging strand is synthesized?

  DNA polymerase I replaces the primer with DNA.
• What is the role of DNA ligase in DNA replication?

  It catalyzes the final phosphodiester linkage between DNA fragments.
• What are telomeres?

  Repetitive sequences at the ends of eukaryotic chromosomes.
• What is the sequence of telomeres in humans?

  TTAGGG-3′, repeated about 2,500 times.
• What happens when the terminal Okazaki primer is removed on lagging strands?

  No DNA can be synthesized to replace it, leading to shorter chromosomes.
• What is telomerase and its role in continuously dividing cells?

  Telomerase catalyzes the addition of lost telomeres in continuously dividing cells.
• Why is telomerase important in cancer cells?

  It allows cancer cells to keep dividing by adding lost telomeres.
• What are the three mechanisms for repairing DNA errors?

  Proofreading, mismatch repair, and excision repair.
• How does proofreading work in DNA repair?

  DNA polymerase recognizes mismatched pairs and removes incorrectly paired bases.
• What is mismatch repair?

  It scans newly replicated DNA for mistakes and corrects mismatches.
• What is excision repair?

  Enzymes scan DNA for damaged bases, excising them and replacing them with correct ones.