A. Transcription

1. mRNA a single strand of nucleotides including purines (A, G) and pyramidines (U, C). DNA is a very long double helix shape that has two sugar – phosphate anti parallel backbones with their bases pointed inwards and connected by H-bonding. Their nucleotides consist of purines (A, G) and pyramidines (T, C)
2. Transcription process:  Unwinding and unzipping of DNA – Complimentary base pairing with DNA – Separation from DNAThe process is carried out by enzyme RNA polymerase. The RNA polymerase (peach candy) begins to untwist and unzip the DNA (the blue pipe-cleaner section that has the gene holding the information to produce a specific protein. The information is stored only on one strand which is called the sense strand. The RNA polymerase runs from the 3′ end of the sense strand to the 5′ end (indicated in the picture), reads the DNA triplets (the three-letter words on the DNA strand) and matches it with the free nucleotides following complimentary base pairing, which will be the codons. However, the Uracil nucleotides (brown) pairs with the Adenine (yellow) on the DNA instead of Thymine (blue). The mRNA formed by the new nucleotides bonding together (the red pipe-cleaner strand) separates from the DNA,  is modified (put caps on, remove introns) before leaving the nucleus.
3. The model generally gives a visual image of RNA transcription. Basic steps in the process is being demonstrated. However, the model is inaccurate in the way how the mRNA is built. We use red pipe-cleaner as the sugar-phosphate backbone for the mRNA, but the mRNA couldn’t have had its backbone before the free complimentary base is called in to bond with the base on the DNA strand. Furthermore, the RNA polymerase is supposed to read the DNA bases in three-letter words, which means working with three bases at a time, not one at a time.

B. Translation

1. Initiation:
   

   The ribosome small subunit binds clings onto the mRNA looking for the start codon (AUG). Then, the two ribosome subunits bind together.

2. Elongation:
   

   The start codon AUG is read at the P-site (the left side). tRNA that has the anti-codon UAC and Methionine comes in and matches up with the codon. A-site is ready for the next tRNA

   

   The next tRNA binds to the next codon at the A-site.

    

   

   The amino acid at the P-site is transfer to the A-site, forming peptide bond with the other amino acid.

   

   The tRNA at the P-site that no longer has its protein leaves the ribosome.

    

   

   The ribosome moves to the next codon and calls in the corresponding tRNA that has the correct anti-codon.

    

   

   The amino acids on the tRNA at P-site are transferred to the tRNA at A-site.

    

   

   The process continues.

3. Termination:
   

   Ribosome detects the stop codon (highlighted), which doesn’t have a tRNA with the right anti-codon.

    

   

   Polypeptide is released, and ribosome dissociates into its subunits.

    

   * The model gives great visual experience of the translation process. The inaccuracies of the model lies in the ribosome. We use the red paper piece as the ribosome, which doesn’t have two subunits. In addition, at the stop codon, a release factor will bond at the site, which we don’t have. Moreover, on one strand of mRNA, there could be many ribosome clinging onto and producing many chains of polypeptide.