Protein Synthesis

PROTEIN SYNTHESIS:

Protein Synthesis is the process that makes protein in cells. mRNA strands and amino acid chains are also created through transcription and translation. The three types of RNA needed to make proteins are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).

A) Transcription

Transcription in the process of which DNA gets converted into mRNA.

3 steps in RNA transcription: Unwinding & unzipping of DNA, complimentary base-pairing, and separation from DNA.

  1. Unwinding & unzipping of DNA:
  • The enzyme, RNA polymerase binds to a specific sequence within the gene, called the promoter, signaling the DNA to unwind.
  • The enzyme will the pry the two DNA strands apart, separating the strands, exposing a gene. One of these strands will be the template strand to generate the mRNA strand and the other is the sense strand.
  1. Complementary base pairing:
  • Once partly untwisted, the RNA polymerase starts to read the template strand and attach its appropriate nucleotide pair, bonding with a hydrogen bond. This is called complementary base pairing. These pairings are different than in DNA replication because with the RNA in transcription, Thymine is replaced with Uracil. So, Adenine will always pair with Uracil, and Guanine with Cytosine.
  1. Separation from DNA:
  • Once several pairings have been made and attached to the backbone, the new strand begins to release/ separate itself from the template strand. The DNA strand will start to wind back up.
  • The new mRNA strand leaves the nucleus through the nucleic pores, and it goes to the ribosome.

B) Translation

The process through which information encoded in mRNA directs the addition of amino acids during protein synthesis.

  1. Initiation:
  • The mRNA strand is now in the ribosome, so the ribosomal subunit attaches to the mRNA to begin reading it. The mRNA is read in groups of 3; “codons”. It looks for the start codon (nucleotides AUG – amino acid Methionine).
  1. Elongation:
  • The ribosome holds the mRNA, while the initiator tRNA enters and attaches its complimentary anticodon to the start codon on the mRNA at the A binding site.
  • The ribosomal subunit keeps reading the next codons, as the initiator tRNA moves to the P-site, getting its corresponding amino acid. A new tRNA comes in and attaches to the mRNA strand through the now empty A-site, with its amino acid.

  • The tRNA in the P-site will detach itself from the mRNA and adds its amino acid to the tRNA in the A-site. That tRNA and chain of amino acid chain will shift over to the now “empty” P-site. This process continues; new tRNA’s entering through the A-site, tRNA in P-site detaches and leaves its amino acid to the tRNA in the A-site, which shifts to the empty P-site etc, etc.

  • The amino acid is decided based on the codon on the mRNA, not the codon on the tRNA because the tRNA is linked to the codon.

           3. Termination:

  • Elongation continues until mRNA “reads” a STOP codon.
  • No new amino acids are added to chain
  • There is no complimentary tRNA with an anticodon for a stop codon on the mRNA strand, therefore, the ribosome stops making the protein sequence.
  • The subunits release the mRNA, tRNA, and the protein that was made.
  • The ribosome dissociates into its 2 subunits.
  • The polypeptide is released

2. Reflection Questions:

A) I think that the models accurately showed how each of the steps of transcription and translation worked, specifically elongation. For me, figuring out what was going on during elongation was very hard just by reading the descriptions and looking at pictures. However, once we understood how to use the models around to show the steps, I found that it was much easier to visualize what is happening. I can now explain the steps much better while imaging and looking back at the models we made. The models were false though in regard to the actual structure/ shape of the molecules. The models were made out of paper, so they were only 2-dimensional, while the real thing is 3-dimensional. This would have made it more realistic and may have given us more information. In terms of changes, like I said, I think a 3D model would be even more useful to picture what is happening in these processes, but also the way we had to put the models together. It took a long time to tape everything together and cut out all the pieces. I think had that been pre-made or had we been given more time for that part, then we would have had more time to figure out the actual steps and how to show them with the models.

B) No, I think there are better ways to educate the public. I think the models worked well for us because we already had some previous knowledge of the processes. However, if this were brand new to people, I do not think that they would understand it just by looking at the models. The steps do not look very different from each other, so without context, I do not think these would make much sense to non-scientific audiences. I think something more like a video would be better to explain protein synthesis for the first time. That way, you could have visuals as well as descriptions to teach these concepts.

Sources:

One Note pages

  • Protein Synthesis – transcription
  • RNA transcription model
  • Translation
  • Translation steps
  • Translation model activity

Protein synthesis powerpoint from in class

In class modeling activies and lessons