Har Gobind Khorana and his colleagues performed numerous experiments translating synthetic mRNAs. In one experiment, an mRNA molecule with a repeating UG dinucleotide sequence was assembled and translated.
How did the polypeptide composition help confirm the triplet nature of the genetic code?

Verified step by step guidance

1. Understand the context: Har Gobind Khorana's experiments involved synthesizing mRNA molecules with specific repeating sequences to study how codons are translated into amino acids. The repeating UG dinucleotide sequence in this experiment is key to understanding the triplet nature of the genetic code.
2. Recognize the repeating UG sequence: The mRNA molecule consists of a repeating UG dinucleotide sequence, which can be represented as UGUGUGUG... This sequence is read by the ribosome in sets of three nucleotides (triplets) during translation.
3. Determine the possible codons: From the repeating UG sequence, the ribosome can form two distinct codons depending on the reading frame: UGU and GUG. These codons correspond to specific amino acids based on the genetic code.
4. Analyze the polypeptide composition: Translation of the mRNA results in a polypeptide composed of alternating amino acids, which correspond to the codons UGU and GUG. This alternating pattern confirms that the genetic code is read in triplets, as the sequence produces distinct amino acids depending on the reading frame.
5. Conclude the significance: The experiment demonstrated that the genetic code operates in a triplet manner, as the repeating UG sequence produced a predictable and consistent polypeptide composition based on the codons formed. This provided strong evidence for the triplet nature of the genetic code.

Key Concepts

Triplet Nature of the Genetic Code

The genetic code is composed of codons, which are sequences of three nucleotides that correspond to specific amino acids. This triplet nature means that each set of three nucleotides in mRNA translates into one amino acid during protein synthesis. Understanding this concept is crucial for interpreting how sequences of nucleotides dictate the structure and function of proteins.

Synthetic mRNA and Translation

Synthetic mRNA is artificially created RNA that can be used in experiments to study translation and protein synthesis. By using a repeating sequence, such as UG, researchers can predict the resulting polypeptide chain. The translation of synthetic mRNA into proteins provides direct evidence of how codons are read and interpreted by the ribosome.

Polypeptide Composition and Codon Analysis

The composition of the resulting polypeptide from the translation of synthetic mRNA can reveal the specific amino acids produced, which in turn confirms the triplet nature of the genetic code. By analyzing the sequence of amino acids, scientists can deduce how many nucleotides correspond to each amino acid, thereby supporting the hypothesis that three nucleotides form a single codon.