DNA, Replication

Pictures:

This picture demonstrates a DNA strand before DNA Replication occurs

This picture shows the DNA being split up by the DNA Helicase (Watermelon slice) and that the DNA Polymerase (Blue Bigfoots) are initiating the duplication of DNA molecules procedure

This picture is the end of a complete DNA Replication procedure which resulted in 2 daughter DNA molecules

Questions:

1. When does DNA Replication occur?

• DNA Replication occurs in the interphase of mitosis

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

• The three steps involved in DNA replication are unzipping/unwinding, complimentary base-pairing, and joining of adjacent nucleotides. Unzipping/unwinding involves the separation of the two DNA strands in an unzipping-like motion by the DNA helicase to disconnect the nucleotides. The next step is complimentary-base pairing where an enzyme called DNA polymerase replicates DNA molecules to create a new DNA strand. After that, another enzyme called ligase completes DNA replication through the joining of adjacent nucleotides by gluing the DNA fragments together. The process is different between the “leading” and “lagging” strands because they are anti-parallel to each other, which means that one strand is the leading strand and the other is the lagging strand. DNA polymerase only operates on the 5’3’ direction, and the leading strand has a 5’3’ direction which makes the replication of DNA molecules from the leading strand much faster. The lagging strand goes at a 3’5’ direction and instead of using the same method on the lagging strand, DNA polymerase copies in a series of segments as the DNA helicase unzips up the DNA strand

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

• For our model, we used coloured beads to represent nucleotides and phosphate bases. This allowed my group and I to organize them in a way that would resemble a DNA strand consisting of nucleotide pairs that were complementary to each other. My group used Bigfoots and slices to represent the enzymes during DNA replication. This activity was well suited when utilizing the pipe cleaners to represent the DNA strands and nitrogen bases because of how they were easily bent. The activity was inaccurate when there was an absence of the primase because it is vital for the DNA polymerase to begin copying the DNA strand.