How were the specific sequences of triplet codes determined experimentally?

Verified step by step guidance

1. Understand that the specific sequences of triplet codes, or codons, were determined by experiments designed to link nucleotide sequences to amino acids in proteins.
2. Review the key experiment by Marshall Nirenberg and Heinrich Matthaei in 1961, where they used synthetic RNA sequences composed of repeating nucleotides (e.g., poly-U) to direct the synthesis of polypeptides in a cell-free system.
3. Recognize that by adding synthetic RNA sequences of known composition to a cell-free translation system, researchers observed which amino acids were incorporated into the resulting polypeptides, thus associating specific triplet sequences with particular amino acids.
4. Learn that by systematically testing different synthetic RNA sequences (e.g., poly-A, poly-C, and mixed sequences), scientists were able to assign amino acids to most of the 64 possible triplet codons.
5. Note that additional techniques, such as using trinucleotide binding assays and sequencing of tRNA anticodons, helped confirm and refine the assignments of codons to amino acids.

Key Concepts

Triplet Code in Genetic Coding

The triplet code refers to the sequence of three nucleotides (codons) in DNA or RNA that specify a single amino acid during protein synthesis. Understanding this code is fundamental to decoding how genetic information translates into proteins.

Experimental Methods for Deciphering the Genetic Code

Early experiments, such as those by Nirenberg and Matthaei, used synthetic RNA sequences to direct protein synthesis in vitro, allowing researchers to link specific triplet sequences to particular amino acids. This approach was key to identifying codon assignments.

Use of Cell-Free Systems and Synthetic RNA

Cell-free systems, which contain the molecular machinery for protein synthesis but lack intact cells, were used with synthetic RNA polymers to observe which amino acids were incorporated into proteins. This method enabled precise determination of codon meanings.