You perform a series of experiments on the synthesis of the pituitary hormone pr
ID: 176634 • Letter: Y
Question
You perform a series of experiments on the synthesis of the pituitary hormone prolactin, which is a single polypeptide chain 199 amino acids long. In the first experiment, the mRNA coding for prolactin is translated in a cell-free protein synthesizing system containing ribosomes, amino acids, tRNAs, aminoacyl-tRNA synthetizes, ATP, GTP, and the appropriate initiation, elongation, and termination factors. Under these conditions, a polypeptide chain 227 amino acids long is synthesized. In a second experiment, the mRNA is translated in the same cell-free system to which you have added SRP. In this case, translation stops after a peptide about 70 amino acids long has been produced. In a third experiment, you use the same cell-free translation system to which you have added both SRP and endoplasmic reticulum vesicles, and you find that that the prolactin mRNA now produces a polypeptide that is 199 amino acids long. Explain these results. Where would you expect to find, the polypeptide produced in experiment 3?Explanation / Answer
A. In experiment 1, after addition of all components require for translational machinary, translation started and performed translation and produced mature protein of 227 amino acid long peptide.
In experiment 2, The function of SRP (Signal Recognition Particle) is couples the translational machinary with translocation process by arresting the translational machinary for a while, the SRP translocate the complex near to the translocon in the endoplasmic raticulum.
When you add SRP, it recognizes the newley synthesizes peptide and arrest the translational machinary after synthesized 70 amino acid containing polypeptide and it didn't find the translocon, which is present in the ER, so it arrested the translational matchinary perminantly.
In experiment3, after added both SRP and ER, protein translation arrested and the peptide inserted into translocon, the SRP is release from the ribosome and then the peptide is translocate into ER, where the signal peptide was cleaved after the protein enter into ER and forms 190 amino acid long peptide.
B. After processed the protein in the endoplasmic reticulum, the protien is shuttled to the golgi apparatus for further modifications inside the cell.
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