Skip to main content
Back

lecture 13

Control buttons has been changed to "navigation" mode.
1/20

Terms in this set (20)

  • What provides the energy for nucleic acid synthesis?
    Hydrolysis of phosphoanhydride bonds in nucleotides (NTPs and dNTPs) provides the energy, releasing pyrophosphate (PPi) which is further hydrolyzed to 2 Pi.
  • What is the DNA polymerase reaction?
    DNA polymerase catalyzes the addition of dNMPs from dNTPs to the 3' OH end of a DNA strand, releasing PPi and using energy from hydrolysis of 2 phosphoanhydride bonds.
  • How many ATP equivalents are used to add one base during DNA synthesis?
    Two ATP equivalents are hydrolyzed per base added, corresponding to the cleavage of two phosphoanhydride bonds.
  • What determines which base DNA polymerase adds?
    Complementarity to the template strand determines the base added by DNA polymerase, which only extends from the 3' OH of the primer strand.
  • What proteins are important for replication initiation?
    Helicase (unwinds DNA), topoisomerase (removes supercoiling strain), single-stranded binding proteins (prevent reannealing), and primase (synthesizes RNA primer).
  • Why are origins of replication rich in A-T base pairs?
    A-T base pairs have weaker interactions (2 hydrogen bonds) than G-C pairs (3 hydrogen bonds), making the DNA easier to unwind at origins.
  • What is the role of primase in DNA replication?
    Primase synthesizes a short RNA primer that provides a 3' OH for DNA polymerase to begin DNA synthesis.
  • Why is one strand of DNA replicated discontinuously?
    Because DNA polymerase synthesizes only 5' to 3', the lagging strand is synthesized discontinuously as Okazaki fragments moving opposite the replication fork.
  • What is the function of the DNA clamp?
    The DNA clamp increases DNA polymerase processivity, allowing it to synthesize thousands of nucleotides without dissociating.
  • How does DNA polymerase proofread during replication?
    DNA polymerase has 3' to 5' exonuclease activity that removes incorrectly added nucleotides by checking base pairing in the minor groove.
  • How are Okazaki fragments joined into a continuous strand?
    DNA ligase seals nicks between Okazaki fragments using energy from ATP hydrolysis, forming phosphodiester bonds.
  • Why can't DNA polymerase fully replicate the ends of linear chromosomes?
    DNA polymerase requires a primer and extends only 5' to 3', so it cannot replicate the very ends, leading to shortening of chromosomes.
  • What is the role of telomerase?
    Telomerase extends telomeres by adding repetitive DNA sequences using an RNA template, allowing complete replication of chromosome ends.
  • What are the three types of RNA in the central dogma?
    Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
  • Which DNA strand is used as the template for mRNA synthesis?
    The noncoding (antisense or template) strand is used by RNA polymerase to synthesize mRNA.
  • What is the relationship between mRNA and the coding strand?
    mRNA sequence is the same as the coding (sense) strand except uracil (U) replaces thymine (T).
  • What is required for transcription initiation?
    Transcription factors bind promoter regions (e.g., TATA box), recruit helicase to unwind DNA, and RNA polymerase binds to start transcription.
  • How does RNA polymerase elongate the RNA transcript?
    RNA polymerase adds nucleotides to the 3' end of the growing RNA strand using energy from hydrolysis of 2 phosphoanhydride bonds per nucleotide.
  • How is transcription terminated?
    Termination occurs via RNA-dependent mechanisms (RNA forms a helix disrupting RNA polymerase) or protein-dependent mechanisms (Rho protein disrupts RNA polymerase).
  • What modifications occur to eukaryotic mRNA after transcription?
    mRNA is processed by adding 5' cap and 3' poly-A tail, and introns are removed by splicing to produce mature mRNA ready for translation.