DNA replication

• where does DNA replication begin

  DNA replication begins at the origin of replication(ori)
• how is the DNA unwinded

  Helicase unwinds the double helix of DNA by breaking the hydrogen bonds between the complementary base pairs in the parental strands
• what is the mode of DNA replication

  semi-conservative replication
• what is semi-conservative replication

  a mode of replication where each parental strand of DNA acts as the template for the synthesis of a new DNA strand, and DNA replication results in 2 DNA molecules where each molecule consists of one parental template strand and one daughter strand
• why is RNA primer synthesised

  the RNA primer is is synthesized to provide free 3' OH ends for DNA polymerase III
• what is the role of primase in DNA replication

  primase attaches to the unwound chain of DNA and catalyzes the synthesis of a short RNA primer to provide free 3' OH ends for DNA polymerase III
• what is the role DNA polymerase III plays in DNA replication

  DNA polymerase III elongates the new daughter strand in the 5' to 3' direction by catalysing the formation of phosphodiester bonds between incoming deoxyribonucleotides and the free 3' OH end of the daughter strand
• how are free deoxyribonucleotides incorporated

  free deoxyribonucleotides are incorporated by complementary base pairing with the parental DNA template strands, with adenine bonding to thymine with 2 hydrogen bonds and guanine bonding to cytosine with 3 hydrogen bonds
• in a replication fork:

  • the leading strand is continuously synthesized
  • the lagging strand is discontinuously synthesized to form Okazaki fragments
• what does the lagging strand consist of?

  the lagging strand is synthesized discontinuously to form Okazaki fragments
• how are the RNA primers removed

  RNA primers are removed and replaced by deoxyribonucleotides by DNA polymerase I
• how about the nicks present in the lagging strand?

  Nicks between the Okazaki fragments are filled in by DNA ligase, which forms phosphodiester bonds between Okazaki fragments
• what direction is DNA replication?

  DNA replication is bidirectional. DNA polymerase III only functions in the 5' to 3' direction, but since DNA is anti-parallel, DNA polymerase III will function in opposite directions to form the leading and lagging strand. hence, DNA replication is bidirectional
• how many points can DNA replication initiate at?

  DNA replication can initiate at many points, forming "bubbles" at each origin of replication which will join to form 2 daughter DNA strands when the "bubbles" expand and overlap