In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
Describe how the codon for phenylalanine was identified.

Verified step by step guidance

1. Understand the context: The genetic code was deciphered using synthetic mRNA sequences in experiments conducted by researchers like Nirenberg and Matthaei. These experiments aimed to determine which codons correspond to specific amino acids.
2. Recognize the experimental setup: In the case of phenylalanine, a synthetic mRNA sequence composed entirely of uracil nucleotides (poly-U) was synthesized. This sequence would look like UUUUUU... (repeating U bases).
3. Explain the translation process: The synthetic poly-U mRNA was added to a cell-free system containing ribosomes, tRNAs, and amino acids, where one of the amino acids was radioactively labeled to track its incorporation into a protein.
4. Describe the observation: When the poly-U mRNA was used, the radioactive phenylalanine was incorporated into the protein, indicating that the codon UUU specifies phenylalanine.
5. Conclude the finding: This experiment demonstrated that the codon UUU in mRNA corresponds to the amino acid phenylalanine, contributing to the understanding of the genetic code.

Key Concepts

Codons

Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids or stop signals during protein synthesis. Each codon is crucial for translating the genetic information encoded in DNA into functional proteins. Understanding codons is essential for deciphering how genetic information is expressed and how specific amino acids, like phenylalanine, are incorporated into proteins.

Synthetic mRNA

Synthetic mRNA refers to artificially created messenger RNA sequences used in experiments to study the genetic code. By introducing these synthetic mRNAs into a system, researchers can observe which amino acids are produced, allowing them to determine the relationship between specific codons and their corresponding amino acids. This method was pivotal in identifying the codon for phenylalanine.

Amino Acid Translation

Amino acid translation is the process by which the sequence of codons in mRNA is translated into a sequence of amino acids, forming a protein. This process occurs during translation, where ribosomes read the mRNA and tRNA molecules bring the appropriate amino acids. Identifying the codon for phenylalanine involved determining which specific codon sequence led to the incorporation of phenylalanine into the growing polypeptide chain.