what would happen if a cell transcribed and translated a gene's intron by mistake?
If a cell were to transcribe and translate a gene's intron by mistake, several consequences might occur:
1. Translation disruption: The transcribed intron would usually contain non-coding sequences (intronic regions) that do not code for proteins. Therefore, translating these non-coding sequences would not produce a functional protein. This would lead to a loss or alteration in the amino acid sequence, potentially affecting the protein's structure and function.
2. Aberrant protein production: The translated intronic region might generate a new protein altogether, which is not usually present in normal cellular processes. This new protein could interfere with normal cellular processes or disrupt the protein-protein interactions necessary for normal physiological functions.
3. Activation of cellular defense mechanisms: The transcribed intron might contain DNA sequences that resemble foreign or viral genetic material, known as pathogen-associated molecular patterns (PAMPs). Cellular defense mechanisms could be triggered, leading to the activation of immune responses such as the production of interferons to combat the perceived foreign DNA.
4. Premature termination of translation: In some cases, the intron might contain a stop codon or other regulatory sequences that prematurely terminate translation. This would result in a truncated or incomplete protein that lacks the essential functional domains, compromising its function.
5. mRNA degradation: Cellular surveillance systems may recognize the presence of intronic sequences during mRNA processing and degrade the mRNA molecule through non-sense-mediated decay (NMD) or other mRNA surveillance pathways. This prevents the translation of aberrant or incomplete proteins and is considered as a cellular quality control mechanism.
Overall, the consequences of transcription and translation of a gene's intron would depend on the specific intronic sequence and the cellular context. In most cases, cells have evolved intricate mechanisms to prevent the inclusion of intronic sequences in the final coding RNA and protein products to ensure the production of functional proteins.