Untranslated regions (UTRs) in mRNA

The correct answer is option 'C', which states that UTRs are the untranslated regions present on mRNA. Let's understand this answer in detail.

Understanding UTRs

Untranslated regions (UTRs) are segments of RNA molecules that are transcribed from DNA but are not translated into protein. These regions are found at both ends of mRNA molecules. UTRs play important roles in the regulation of gene expression, mRNA stability, localization, and translation efficiency.

UTRs at the 5' end of mRNA (5' UTR)

The 5' UTR is the region on mRNA that is upstream (towards the 5' end) of the start codon. It contains various regulatory elements, including binding sites for proteins and non-coding RNAs. The 5' UTR interacts with translation initiation factors and ribosomes to regulate protein synthesis. It also participates in mRNA localization and stability.

UTRs at the 3' end of mRNA (3' UTR)

The 3' UTR is the region on mRNA that is downstream (towards the 3' end) of the stop codon. It is longer than the 5' UTR and contains important regulatory elements. The 3' UTR is involved in post-transcriptional regulation, including mRNA stability, degradation, and translation efficiency. It contains binding sites for microRNAs (miRNAs) and RNA-binding proteins (RBPs). miRNAs can bind to complementary sequences in the 3' UTR and regulate mRNA stability and translation. RBPs can interact with the 3' UTR to influence mRNA localization, stability, and translation.

UTRs and gene expression

UTRs play a crucial role in the regulation of gene expression. They contain cis-regulatory elements that interact with trans-acting factors to control mRNA processing, transport, localization, stability, and translation. By interacting with various proteins and non-coding RNAs, UTRs contribute to the fine-tuning of gene expression in response to cellular signals and environmental cues.

In conclusion, UTRs are the untranslated regions present on mRNA molecules. They are involved in the regulation of gene expression, mRNA stability, localization, and translation efficiency. The 5' UTR is located upstream of the start codon, while the 3' UTR is located downstream of the stop codon.