Question

In the in vitro translation system, is it possible for bacterial cell components used in translation such as Ribsomes, tRNA, and aminos acids, to be used with the addition of eukaryotic mRNA to produce a protein? Explain it in as clear terms as possible.

Answer 1

Eukaryotic mRNA is traveled into the cytosol from the nucleus after transcription to get translated into a protein. When the mRNA is in the cytosol ribosomes smaller sub unit first comes and gets attached to the mRNA and then slowly the larger sub unit also gets attached. Ribosomes act as an enzyme that usually functions in catalyzing the reaction in linking the amino acid chain together. The ribosome has three sites known as A site, P site and E site. A site is the aminoacyl tRNA site, P site is the growing polypeptide chain site and the E site is the Exit site. The incoming tRNA has an anticodon that is complementary to the codon that is present on the mRNA. The incoming tRNA has the anticodon complementary to the codon on the mRNA and also carries the amino acid corresponding to the codon that is present on the mRNA and loads it on the A site of the ribosome. The function of tRNA is to load correct amino acid corresponding to the codon that is present on the mRNA. For example the codon on the mRNA is 5' - AUG - 3' that codes for methionine so, the tRNA has 3' - UAC - 5' on one end and methionine that is the amino acid coded by AUG on the other end. This is known as initiation complex and this step is known as Initiation.

Now, the first tRNA carrying methionine comes and binds at the P site and gets activated and the tRNA is now charged and is known as aminoacyl tRNA. The next incoming amino acids comes and binds to the A site and then this second amino acid is translocated into the P site and the empty tRNA leaves the ribosome through the E site. There is formation of a peptide bond between methionine and the second amino acid by the formation of a peptide bond and thus the peptide chain grows. This process continues, when the amino acid on the A site is translocated on to the P site, the A site is left empty and the incoming amino acid now comes and binds at the A site and the amino acid from the A site is now translocated from A site to the P site along with the tRNA and then this amino acid forms a bond with the pre existing amino acids, and now the empty tRNA without the amino acid is translocated into the E site and eventually leaves the ribosome. This step is known as Elongation.

When there is a STOP codon present on the mRNA that is when there is termination of the protein synthesis. When the tRNA encounters a STOP codon it cannot carry any amino acid because STOP codons do not code for any amino acids. So, when there is presence of the STOP codon translation terminates and the protein is released. This step is known as Termination.

There are ideally three steps in the Eukaryotic protein synthesis that is translation that is INITIATION, ELONGATION AND TERMINATION.