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1. Explain the structure of DNA.

Deoxyribonucleic acid also is also known as DNA is made up of monomers called nucleotides which are composed up of a 5-carbon sugar, a phosphate group and a nitrogenous base (Purines: Adenine, Guanine, and Pyramindines: Cytosine, and Thymine). DNA is made up of two antiparallel strands going in opposite directions but sending the same messages. This is represented in the photos by having one strand start with phosphate and one starts with sugar. The sugar is represented by a pink bead. Our model of the DNA has a minor mistake the Adenine and the Guanine should be represented by two beads as they are a purine with a double-ringed structure as opposed to the pyrimidines which have a single-ringed structure. The complementary base pairings are the nitrogenous bases that join together to form the DNA and a specific purine will always have a specific pyrimidine ( Adenine and Thymine together and Cytosine and Guanine together). These can be in mixed order, however, the A will always be with T and the C will always be with G in DNA.

2. How does this activity help model the structure of DNA? What changes could we make to improve the accuracy of this model?

This activity helps model the structure of DNA as we can clearly see all the important details that could be missed when just reading about DNA. This clearly demonstrates that DNA is antiparallel and one strand starts with sugar while the other starts with phosphate. Furthermore, this activity helps us memorize the base pairings and see the various steps of DNA as we create the model. Some changes to be made to help improve the accuracy of this model would be to bring things slightly more the scale. Of course, not it could not be exact as DNA is so incredibly small, however, ensuring the white pipe-cleaners are slightly more to scale to the beads and blue pipe-cleaners could help us visualize clearly what DNA looks like and functions in real life.

3. When does DNA Replication Occur?

DNA replication occurs immediately before cell division as it is needed for the cell to divide. DNA replication is necessary for all living organisms as it is what allows the genetic information to passed down and inherited to the next organism. DNA replication is known as a semi-conservative process as the replicated DNA contains part of the “old/original” DNA and also a “new/replicated” strand of DNA to create a new strand of DNA in a double-helix form.

4. Name and Describe the 3 Steps Involved in DNA Replication. Why Does the Process Occur Differently on the “Leading” and “Lagging” Strands?

Unwinding and Unzipping

• This is considered the first step in DNA replication. This is when DNA Helicase moves along the center of the strand and unravels the double helix structure to make more a ladder structure and moves along the complementary base pairings to break the bonds between them and separate the DNA completely. DNA helicase is an enzyme built to unzip the DNA in DNA replication.

Complementary Base Pairings

• The enzyme Polymerase uses the new complementary nucleotides (present in the nucleus) and pairs them with the original strand that was unzipped. DNA Polymerase can also only build from 5′ to 3′. It can start on the 3′ to 5′ original strand and work down, this is known as the “leading” strand. However, with the other original strand being 5′ to 3′, DNA Polymerase has to build in the reverse direction by making fragments since it only builds 5′ to 3′. This creates Okazaki fragments (Okazaki fragments are short sequences of DNA nucleotides that are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication). As DNA Polymerase works to build on this strand, there are constant interruptions along it making it known as the “lagging” strand.

Adjacent Nucleotides Joining

• This is known as the final step in DNA replication. In this step, the complementary base pairings are bonded together with the sugar-phosphate backbone to form a new DNA strand. The enzyme DNA ligase goes along the lagging strand to join together the DNA and repair the Okazaki fragments. The DNA then winds into a double-helix and this the replica of the DNA.

5. What Did You do to Model the Complimentary Base Pairing and Joining of Adjacent Nucleotide Steps of DNA Replication? In What Ways was This Activity Well Suited to Showing This Process? In What Ways Was it Inaccurate?

The way our group modeled each step of DNA replication was undoing the original strand of DNA and half hooking it to the “new/replicated” strand of DNA; therefore, showing that it is bonding to a new strand but not yet completed. To represent the stage of Adjacent Nucleotides steps with fully hooked together with the new strands of DNA to show the complete replication of DNA. This activity was well suited to show the complete process in each individual step as we needed to be able to assemble what each step looked like. However, this activity was inaccurate as you cannot model the Okazaki Fragments within the lagging strand of DNA and it cannot model the DNA Ligase moving along the lagging strand to repair any Okazaki Fragments.