What experimental evidence provided the initial insights into the compositions of codons encoding specific amino acids?

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Understand that the question asks about the experimental evidence that first revealed how codons correspond to specific amino acids in the genetic code.

Recall that the key early experiments involved deciphering the genetic code by determining which sequences of nucleotides (codons) specify particular amino acids during protein synthesis.

Focus on the experiments by Marshall Nirenberg and Heinrich Matthaei in 1961, where they used synthetic RNA sequences in a cell-free system to direct the synthesis of polypeptides.

Note that they created artificial RNA sequences composed of repeating nucleotides, such as poly-U (uracil), and observed which amino acids were incorporated into the resulting polypeptides, linking specific codons to amino acids.

Recognize that this approach of using synthetic RNA and cell-free translation systems provided the first direct experimental evidence connecting codons to their corresponding amino acids.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

The Genetic Code and Codons

The genetic code consists of codons, which are sequences of three nucleotides in mRNA that specify particular amino acids during protein synthesis. Understanding that codons are triplets is fundamental to linking nucleotide sequences to amino acid sequences.

Nirenberg and Matthaei's Poly-U Experiment

This landmark experiment used synthetic RNA composed solely of uracil bases (poly-U) to direct protein synthesis in vitro, resulting in a polypeptide of phenylalanine. It provided the first direct evidence that specific codons correspond to specific amino acids.

In Vitro Translation Systems

In vitro translation systems allow researchers to study protein synthesis outside living cells by providing mRNA templates and necessary components. These systems were crucial for testing synthetic RNAs and identifying which amino acids were incorporated, revealing codon assignments.

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How were the specific sequences of triplet codes determined experimentally?

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How were the experimentally derived triplet codon assignments verified in studies using bacteriophage MS2?

Textbook Question

Why did geneticists believe, even before direct experimental evidence was obtained, that the genetic code would turn out to be composed of triplet sequences and be nonoverlapping? Experimentally, how were these suppositions shown to be correct?

Textbook Question

Write a short essay that summarizes the key properties of the genetic code and the process by which RNA is transcribed on a DNA template.