Rate of Protein Synthesis

In E.coli, the DNA transcribes mRNA for enzymes controlling tryptophan synthesis at the rate of about 28 nucleotides per second at 37C. Protein is translated from the mRNA at the rate of about 7 amino acids per second.

Translation fo the hemoglobin polypeptide chain takes place at the rate of about 4 amino acids per second. The complete polypeptide chain is translated by mRNA in 35 seconds.

In salemonella typhimurium the histidine operon contains 10structural genes. These genes transcribe one long polycistronic mRNA molecule of about 13,000 nucleotides which codes for all the enzymes of the histidine locus. Theoretically all the 10 enzymes should be synthesized in equal quantities. It has been found, however, that the frequency of synthesized of enzymes at one end is greater than that of enzymes at the other end. Translation of mRNA begins at the G end. Pryophosphorylase, which is translated at the G end, is more frequently synthesized than isomerase which is translated at the other end. This has been explained as follows: since translation begins at the G end, genes at the opposite end are less likely to be translated because of accidental breakdown of ribosomes of mRNA.




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