Genetic Code

The process of fully decoding and verifying the genetic code involved rigorous experimentation and theoretical work to understand how sequences of nucleotides in DNA and RNA correspond to specific amino acids, which in turn build proteins. Here's a more detailed look into this fascinating process:

Experimental Deciphering

The Poly-U Experiment by Nirenberg and Matthaei (1961)

• Experiment: Marshall Nirenberg and Heinrich Matthaei synthesized a simple RNA strand composed solely of the nucleotide uracil (poly-U). They added this RNA to a test tube containing ribosomes, the protein-making machinery of the cell, and other necessary components for protein synthesis.

• Discovery: The experiment resulted in the production of a polypeptide chain composed entirely of the amino acid phenylalanine, demonstrating that the codon UUU corresponds to phenylalanine.

• Impact: This was a groundbreaking discovery because it was the first time a specific sequence of RNA was shown to code for a particular amino acid, confirming the idea that nucleotide triplets (codons) dictate protein synthesis.

Contributions of Ochoa and Khorana

• Severo Ochoa: Developed techniques to synthesize RNA with defined sequences, allowing for systematic testing of codon-amino acid relationships. His work facilitated the production of synthetic RNA sequences, essential for decoding the genetic code.

• Har Gobind Khorana: Developed methods to create RNA molecules with specific sequences. Khorana's work was crucial in confirming the assignment of codons to specific amino acids by synthesizing RNA sequences and observing the resulting polypeptides.

  • Example: Khorana synthesized repetitive nucleotide sequences, such as UCUCUCUCUC, which produced a polypeptide with alternating serine and leucine, confirming the coding properties of these sequences.