Question

Which of the following choices does not support the notion that the gene is much more than DNA sequences that are transcribed into a single RNA molecule that encodes a single polypeptide?

1) Alternative splicing–a single gene can yield multiple mRNA and protein products.
2) A single ribosomal RNA transcripts can liberate several RNA molecules via further processing
3) RNAs can be the functional product of a gene without being translated into protein product
4) Protein coding region–each codon represents specific amino acid that will be linked to form a polypeptide
5) Regulatory elements are part of a gene that regulate timing, degree, and specificity of gene expression but are not transcribed.

Answer 1

Choice 4, the protein coding region linking codons to a single polypeptide, does not challenge the notion that a gene's role extends beyond simple transcription into protein. Alternative splicing, regulatory elements, and RNA products like rRNA and tRNA demonstrate the multifunctional nature of genes.

Step-by-step explanation:

To support the notion that a gene is much more than simply DNA sequences that are transcribed into a single RNA molecule to encode a single polypeptide, we must consider several factors beyond the basic transcription and translation processes. The following points elaborate on this complexity:

Alternative splicing – This process allows a single gene to produce multiple mRNA and, subsequently, different protein variants. Hence, a gene's functionality is not limited to producing just one type of protein.

A single ribosomal RNA (rRNA) transcript can be processed to yield several rRNA molecules, which indicates that a gene's role can extend to generating multiple functional RNA products that don't necessarily encode proteins.

Some RNA molecules, such as rRNA and tRNA, are functional end products of gene expression that do not result in protein products, thereby showing that genes have roles beyond coding for proteins.

The protein coding region specifies which amino acids will comprise a polypeptide, through the use of codons, supporting the original definition of a gene as a sequence that leads to a polypeptide chain.

Regulatory elements may be part of a gene's structure. These elements play crucial roles in determining when, how much, and in what cells a gene is expressed, although they are not themselves transcribed into RNA.

Therefore, choice 4, "Protein coding region – each codon represents a specific amino acid that will be linked to form a polypeptide," does not challenge the notion that a gene is more than a simple DNA to protein blueprint. Each of the other choices provides evidence that genes are multifunctional and can lead to multiple RNA and protein products, play roles in regulatory functions, and have non-coding elements with crucial roles in gene expression.