Daily Archives: March 2, 2018

DNA and Protein Synthesis Part 4

Posted on by
1

  1. 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.
  2. 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.

DNA and Protein Synthesis Part 3

Posted on by
1

  1. 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.
  2. 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.
  3. 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.