Which of the following correctly describes an exon?

An exon is defined as a segment of DNA that is expressed, meaning it is part of the gene that gets translated into protein. During the process of gene expression, exons are the sequences that remain in the mRNA after splicing, while non-coding sequences, known as introns, are removed. The presence of exons is critical because they contain the necessary information that dictates amino acid sequences to form proteins. Each exon can encode for specific functional parts of a protein, contributing to its structure and function, thereby playing an essential role in the overall mechanism of protein synthesis in cells.