Translation occurs in 3 steps; initiation, elongation, and termination. During initiation, mRNA binds to a ribosome subunit which then binds to another ribosome subunit. The ribosome subunit then scans the mRNA for a start sequence which begins translation. Next, during elongation, the ribosome subunit holds the mRNA in place while complementary tRNA is attached to the binding sites. mRNA contains a 3 letter code called a codon while the tRNA contains a complementary code called an anti codon. Each codon is specific to one of the 20 amino acids. tRNA binds to the “P” site, while another tRNA binds to the “A” site. This binding causes change which results in the amino acid letting go of the tRNA and binding to the neighbouring amino acid. Then, the empty tRNA leaves the ribosome as it moves along the mRNA. As the ribosome moves along, the 2nd tRNA goes to the “P” site and new tRNA binds to mRNA at the “A” site. Finally, termination occurs which is when the mRNA reads a stop codon which does not have a matching tRNA. This codon puts an end to the elongation cycle, and since no new amino acid is added to the chain, the ribosome dissociates into its 2 subunits and the polypeptide is released.
The model did a good job of showing every step clearly and what happened during those steps. There was nothing majorly inaccurate about the model.
mRNA is different than DNA in many ways. For example, mRNA is a single sided strand where DNA is double strand. Also, mRNA is much smaller in size than DNA since it has to be small enough to move in and out of the nucleus. By being able to move around, the DNA can stay in the nucleus while the mRNA copies the DNA and carries it to the ribosomes in order to carry out transcription.
The process of transcription can be broken into 3 phases; unwinding and unzipping of DNA, complementary base pairing with DNA, and separation from DNA. In the unwinding and unzipping of DNA, RNA polymerase untwists the DNA alpha helix shape. Then, the mRNA nucleotides are paired up with the complementary nucleotides from the DNA strand. Finally, once the mRNA has copied the DNA, it leaves the nucleus as the DNA returns to its original form without any harm done to it.
By modelling this, it was easy to see the first two steps of transcription without any problem. It was clear what was happening and the role of the RNA polymerase. However, it was difficult to model how the mRNA copies the DNA and then leaves the nucleus. It also was an inaccurate representation of the size difference between mRNA and DNA.
DNA replication occurs before mitosis because the cell realizes that it is becoming too big so it has to divide in order to keep doing its function. If the cell were to grow any bigger, it would not be able to do it’s job, so it divides into two daughter cells.
The 3 steps involved in DNA replication are unwinding and unzipping, complementary base pairing, and the joining of opposite nucleotides. In the first step (unwinding and unzipping) a DNA helicase breaks the Hydrogen bonds which hold the nucleotides together. Once the bonds are broken by the helicase, the DNA structure unwinds. Then in complementary base pairing, DNA polymerase match the opposite nucleotides together; Adenine bonds with Thymine and Guanine bonds with Cytosine. Finally, in the final step, (joining of nucleotides) DNA ligase put these nucleotides together and creates two new strands of DNA. The 3 steps are different on the “leading” and “lagging” strands because the DNA polymerase can only read the DNA strand from 3′ to 5′ which means the lagging strand has to be read backwards. The “leading” strand is the one with the extra sugar at the beginning.
By modelling these, we were able to represent how the hydrogen bonds break apart and the steps that follow. By using different candies, we were able to represent the polymerase, helicase, and ligase and there job pretty accurately. However, it was hard to tell which strand was the leading and lagging one based on the model. Also, since we used blue pipe cleaner for all the DNA strand backbones, you never got a clear picture of which one was the parent DNA strand vs the daughter strand.
DNA has an alpha helix shape which consists of nucleotides. Nucleotides are made of pentose, phosphate, and a nitrogenous base. They have 2 types of bases; purines and pyrimidines. Pyrimidines consist of a single ring structure with thymine and cytosine while purines have a double ring structure with adenine and guanine. Since there is complementary base pairing between the nucleotides adenine and thymine as well as guanine and cytosine, they bond together to create the alpha helix shape that DNA has. DNA also consists of antiparallel strands meaning that the sugar and phosphate are aligned in opposite directions on each backbone of the DNA helix.
The activity helps model the structure as it clearly shows the nucleotides and how they bond together to create the double helix shape. However, it is hard to see that the backbone contains sugar as well as phosphate. Next time we should add a different colour bead for sugar and also maybe use a different colour bead for the phosphate so it can stand out better from the blue pipe cleaner.
