Image 1 is a model of DNA. DNA stands for deoxyribonucleic acid and it is made out of sugars (deoxyribose), phosphates and nitrogen bases. DNA has two backbones which is formed by bonded sugar-phosphate portions, with nitrogen bases connecting to each other. In image 2, we see one backbone of a DNA strand and in image 1, two backbones are joined together by the rungs formed by the hydrogen bonds between the nucleotide base pairs, which is called complimentary base pairing. There are four different bases in DNA and they categorize in pyrimidines or purines. Adenine and guanine are purines and they are composed of two rings. Thymine and cytosine are pyrimidines and they have only one ring. The two strands in DNA are antiparallel as the strands can give the same message but one strand has the reverse message due to the strands going in opposite directions. Image 3 shows the DNA winded up as a double helix. In the model, we showcased the backbones as blue pipe cleaners, h-bonds with white pipe cleaners, adenine with yellow beads, guanine with purple beads, thymine with blue beads, cytosine with green beads, and phosphate with pink beads. The model is good at showcasing a simple 3d diagram of DNA which helps us understand the shape of the DNA and how the two strands connect with each other. However, the 3d model is somewhat hard to follow as it can get confusing what each bead or pipe cleaner represents. It is also misleading that the white pipe cleaner is binding the bases to the backbone because the bond between the bases and the backbones are not hydrogen bonds. Labeling each bead with a letter (for example A for adenine) might help the person remember what each bead represents.

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When DNA replicates, it is semiconservative. This means each DNA strand separate from each other and the strands are used as a template for the creation of a new strand, making two DNA with one old strand and one new strand. This process occurs before the cells enters mitosis. DNA replication happens in three stages: unwinding, complimentary base pairing, and joining. First, during unwinding the double helix unwinds and the DNA helicase breaks the hydrogen bonds between the base pairs to separate the DNA strands. This is shown in image 4 as the green Play-Doh represents the DNA helicase. Second, during complimentary base pairing, DNA polymerase facilitates the process as extra floating nucleotides in the nucleus move to hydrogen bond with the partner base. This is shown in image 5 as the orange Play-Doh represents the DNA polymerase. Since DNA is antiparallel, when DNA polymerase is facilitating the pairings, it can only read in the 5′ to 3′ direction which causes a leading strand and a lagging strand. The leading strand is faster as it is continuous as the DNA “unzips” and the lagging strand is slower and leaves fragments. Finally, during joining the nucleotides on the new strand form covalent bonds, and the DNA ligase glues the fragments left from the lagging strand. This is shown in image 6 as the red Play-Doh represents the DNA ligase. After the replication, the result is two daughter DNA molecules with each containing one strand from the parent and one new strand, and both are identical to the original. This model is good at showcasing the steps at unwinding and joining as it is simple to picture an enzyme cutting the hydrogen bonds and joining fragments of strands together. The model gets hard to understand and show in the complimentary base pairing step because it is hard to showcase and identify which strand is the leading strand or lagging strand. Also, the model does not show the floating nucleotides that is always present in the nucleus.

Image 4                       Image 5                       Image 6