You perform a series of experiments on the synthesis of the pituitary hormone pr

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 synthetases, 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 the prolactin mRNA now produces a polypeptide that is 199 amino acids long. A) Explain these results. B) Where would you expect to find the polypeptide produced in experiment 3?

Explanation / Answer

1)In first experiment though Termination factors were there,still they couldn't Terminate as there All necessary resources available to Go on and theres no SRP! 2)SRP interferes with Translation, hence in Expt. 2 it Terminated at 70 Amino Acids. 3)In Third Expt. as there is both SRP which terminates, but its termination this time is Delayed by ER Vesicles. Hence it undergoes optimal Translation. Prolactin is secreted by "Neurosecretory Tuberoinfundibulum (TIDA) Neurons of the Arcuate nucleus" in Hypothalamus, then it come to Pituitary and released...

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