Question

The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, but the use of UAUC incorporates four amino acids. Why?

Short answer

Answer: The mRNA formed from the repeating tetranucleotide UUAC incorporates three amino acids, while the mRNA formed from the repeating tetranucleotide UAUC incorporates four amino acids.

Step-by-step solution

Understand the Genetic Code

The genetic code is a set of rules that define how the four-letter genetic alphabet (A, C, G, and U) is translated into the 20-letter amino acid alphabet. The code is composed of three-letter "codons" in the mRNA, each of which corresponds to a specific amino acid. There are 64 different codons, and three of these (UAA, UAG, and UGA) are known as "stop codons," meaning they do not code for any amino acids and instead signal the end of translation.

Analyze the Repeating Tetranucleotide UUAC

When we analyze the repeating tetranucleotide UUAC, we must split it into three-letter codons to see which amino acids are coded for. If we start from the first base, we get the codons UUA and UAC, which code for the amino acids Leucine and Tyrosine, respectively. If we start from the second base, we get UAC and UUA, which are the same codons we obtained from the first frame. Thus, the mRNA formed from UUAC incorporates only three amino acids: Leucine, Tyrosine and a stop signal (the third codon).

Analyze the Repeating Tetranucleotide UAUC

Now, let's analyze the repeating tetranucleotide UAUC. If we start from the first base, we get the codons UAU and CUA, which code for Tyrosine and Leucine, respectively. If we shift to the second base, we get the codons AUC and UAU, which code for Isoleucine and Tyrosine, respectively. So, in this case, the mRNA formed from UAUC incorporates four different amino acids: Tyrosine, Leucine, Isoleucine, and a stop signal (the third codon).

Conclusion

The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, while the mRNA formed from the repeating tetranucleotide UAUC incorporates four amino acids. This difference is due to the distinct codon combinations produced from the different tetranucleotide sequences and how they are translated in the genetic code.