Chapter 5

• DNA ligase connects nucleotides by rejoining the phosphodiester backbone
• SSB—Single-strand DNA binding protein
  • Exposed single-strand DNA (ssDNA) is easily coiled or degraded.
• Sliding clamp (PCNA) and clamp loader maintain the connectivity for leading and lagging strands.
• DNA topoisomerase I and II help to keep the DNA from rotating with helicase.
• Origins of replication (ori)
  • DNA sites that initiate the creation of replication forks
  • Marked by a high density of AT sequences
  • Recruits initiator proteins
  • Ori's are important for speed and efficiency with how large the human chromosome is.
  • Not every ori is used, but every ori has the ability to be used.
  • New histones are synthesized specifically during the S phase of the cell cycle.
    • DNA duplication of interphase
  • When a replication fork hits a nucleosome, the chromatin remodeling complexes break apart and re-forge nucleosomes
  • The octamer breaks into the H3/H4 tetramer and H2A,B dimers.
• Histone chaperones
  • CAF1
    • Chromatin assembly factor
  • NAP1
    • Nucleosome assembly protein
• Telomeres
  • “GGGTTA”—Repeat sequence
    • Repeated 1000 times at the end
  • A cell cannot distinguish between telomere DNA and broken DNA.
  • Shelterins
    • Recognize telomere ends (GGGTTA) and create telomere T-loops
• DNA Repair