Question

Silent RNA. The code word GGG cannot be deciphered in the same way as can UUU, CCC, and AAA, because poly(G) does not act as a template. Poly(G) forms a triple-stranded helical structure. Why is it an ineffective template?

Answer 1

Poly(G) RNA forms a triple-stranded helical structure which inhibits its function as a template for protein synthesis by preventing tRNA from recognizing and binding to it. Translation relies on single-stranded RNA for the tRNA to read the triplet codons effectively.

Step-by-step explanation:

The triple-stranded helical structure formed by poly(G) RNA sequences renders it an inefficient template. The Guanine (G) bases bond with each other in a way that creates a triple helix, which prevents the RNA from being used effectively during transcription and translation. In the central dogma of molecular biology, RNA acts as a template for protein synthesis, with triplet codons corresponding to amino acids.

Each codon is a unique sequence of three nucleotides in mRNA that specifies an amino acid or a termination signal for protein synthesis. For example, UUU codes for phenylalanine, CCC for proline, and AAA for lysine. However, when the poly(G) sequence forms a triple helix, the template cannot be read correctly to direct the assembly of amino acids into a protein.

Thus, the effectiveness of an mRNA template relies on its ability to remain single-stranded so that tRNA molecules can recognize and bind to the codons during translation. GGG codons, when polymeric, disrupt this process by forming triple helices that are incompatible with the cellular machinery needed for protein synthesis.