DNA replication occurs during the synthesis phase of interphase.

 

2. Name and describe 3 steps involved in DNA replication. Why does this process occur differently on the ‘leading’ and ‘lagging’ strands?

 

• Unwinding: The helix unwinds and the two backbone strands unwind from its double helix shape(the h-bonds break). The DNA enzyme helicase causes this ‘unwinding’.
• Complementary base pairing: Nucleotides that are present in the nucleus move into place and form h-bonds with their new partner(A to T and C to G). The DNA enzyme polymerase helps these new pairs join.
• Joining: Nucleotides form covalent bonds( due to polymerase) and two identical daughter strands are formed.

This differs in the leading and lagging strands because the leading strand can smoothy continue joining new nucleotides in the 3’ to 5’ direction, but the lagging strand goes against this smooth running direction, so it creates new nucleotides in small sections.

 

3. The model today wasn’t a great fit for the process we were exploring. What did you do to model the complementary base pairing and joining of adjacent nucleotide steps of DNA replication. In what way was this activity well suited to showing this process? In what ways was it inaccurate?

 

To model the complementary base pairing, we represented it as the ‘unzipped’ nucleotides with their phosphate and sugar groups with their nitrogen bases facing outward, and the new strand with the complementary base for the parent strand beginning to join. We then used the bunny candy to represent the polymerase enzyme that helps these new partners join. To model joining of the nucleotides we showed the end of the process with the finished identical daughter molecules with the heart candy representing the ligase enzyme that helped this process along. This activity was well suited for showing these processes with the way the pipe cleaner could be manipulated to face outwards to show the joining of the new complementary bases.  It was inaccurate because it was difficult to place the candy on the pipe cleaner to represent the enzymes, and to represent the differences between the complementary base pairing and the joining of the nucleotides.