What does a coding sequence refer to in mRNA?

A coding sequence in mRNA specifically refers to the part of the mRNA that is translated into a protein. It consists of a series of codons, which are groups of three nucleotides that correspond to specific amino acids. This sequence dictates the order in which amino acids are linked together to form a polypeptide chain, ultimately folding into a functional protein. Understanding the coding sequence is crucial, as it directly determines the characteristics and functions of the resulting protein, influencing nearly every biological process.

The other options describe different aspects related to mRNA but do not define the coding sequence itself. Introns, for instance, are non-coding regions that are usually spliced out before translation occurs. The ribosome binding site is vital for the initiation of translation but is not part of the coding sequence itself. Finally, the ending sequence of mRNA pertains to regions like the poly-A tail or terminator signals, which are important for stability and regulation rather than coding for amino acids.