Coupling of transcription and translation — estimating protein synthesis rate In prokaryotes, translation speed is limited by the rate of mRNA synthesis. If RNA polymerase synthesizes mRNA at 50 nucleotides per second, what is the approximate rate of protein synthesis in amino acids per second?

Introduction:
In bacteria, transcription and translation are physically and temporally coupled. The ribosome often trails closely behind RNA polymerase on the same mRNA. Hence, the nucleotide synthesis rate can constrain translation speed when tightly coupled.

Given Data / Assumptions:

• mRNA is synthesized at 50 nucleotides per second.
• Each codon consists of 3 nucleotides and encodes one amino acid.
• We neglect pauses and assume continuous coupling for estimation.

Concept / Approach:

Convert nucleotide rate to codon rate by dividing by 3, because 3 nucleotides form 1 codon. The codon rate equals the maximum amino acid incorporation rate under tight coupling.

Step-by-Step Solution:

Verification / Alternative check:

Empirical measurements in Escherichia coli show elongation rates commonly around 15–20 aa/s at moderate temperatures, matching the computed 17 aa/s.

Why Other Options Are Wrong:

10 aa/s underestimates for the given transcription rate. 25 and 50 aa/s exceed the codon supply rate. 150 aa/s is far above typical bacterial rates under standard conditions.

Common Pitfalls:

Forgetting to divide by 3 nucleotides per codon or confusing nucleotides with amino acids directly.

Final Answer:

17 amino acids per second