Semi-Conservative DNA Replication

• how does the double helix unzip during DNA replication?

  DNA helicase enzymes separate the 2 strands by hydrolysing the hydrogen bonds between the bases
• what happens after the DNA unzips?

  free, activated nucleotides attach onto the exposed nucleotides on the original template strands, because they're complementary
• why are free nucleotides known as activated nucleotides?

  they contain 2 extra phosphates
• what happens after the activated nucleotides attach onto the template strands?

  the DNA polymerase enzyme moves up the strands to form phosphodiester bonds between the activated free nucleotides
• what provides the energy to form the new phosphodiester bonds?

  breaking the phosphates off the activated nucleotides
• what are the 2 DNA strands called?

  leading continuous template strand

  lagging template strand
• why is the 3'-5' strand known as the lagging template strand?

  the DNA polymerase enzyme can only move in the 5'-3' direction, so it completes the lagging strand in small, disconnected sections called okazaki fragments
• which enzyme forms phosphodiester bonds between the okazaki fragments?

  DNA ligase
• what are point mutations?

  when a single base is copied/replicated incorrectly
• are point mutations usually dangerous? why?


  no

  enzymes usually spot and correct these mutations during replication
• how does hydrogen bonding allow DNA to replicate?

  they break and form easily
• why do purines only bind to pyrimidines?

  they are different sizes