Final answer:
miRNAs are not translated because their role is to regulate gene expression, not to serve as templates for protein synthesis. They interact with RISC to target mRNAs for degradation or inhibit their translation. Unlike mRNAs, miRNAs lack features like a start codon and ribosome binding sites that are necessary for translation.
Step-by-step explanation:
miRNAs are not translated into proteins because their primary function is to regulate gene expression by targeting specific mRNAs for degradation or inhibiting their translation. This process is key to controlling the levels of proteins within the cell. Although miRNAs and mRNAs are composed of the same nucleotides, miRNAs are structurally different as they are short RNA molecules, usually 21-24 nucleotides in length, and lack the features required for translation.
mRNAs, on the other hand, undergo processing that includes splicing, 5' capping, and addition of a poly-A tail, which are essential for the stability of the mRNA and its recognition by the ribosome for translation. RISC (RNA-induced silencing complex) is crucial in the function of miRNAs. Mature miRNAs are loaded onto RISC, which then binds to target mRNAs, leading to the inhibition of their translation or degradation.
MiRNAs do not have a start codon and are not designed to engage with ribosomes to initiate the translation process, unlike mRNAs, which contain start codons that signal initiation of translation at the ribosome.