How do introns and exons differ in eukaryotic genes?

Introns are non-coding sequences within a gene, while exons are coding sequences that contribute to the final protein product.

In eukaryotic genes, the structure is typically composed of alternating sequences of introns and exons. Introns, short for 'intervening sequences', are segments of DNA that do not code for proteins. They are transcribed into RNA but are later removed during the process of RNA splicing. This means that although they are part of the initial transcript, they do not contribute to the final protein product. Introns can vary greatly in size and can sometimes make up a significant portion of a gene. Despite not coding for proteins, introns are not 'junk DNA'. They play crucial roles in gene regulation and evolution.

On the other hand, exons, short for 'expressed sequences', are the segments of a gene that are transcribed into RNA and then translated into proteins. They are the coding regions of a gene and their sequences directly determine the amino acid sequence of the protein product. During RNA splicing, the exons are joined together to form the mature messenger RNA (mRNA) that is then used as a template for protein synthesis. The number of exons in a gene can vary, and the combination of different exons can lead to different protein products, a process known as alternative splicing.

The presence of introns and exons in eukaryotic genes is one of the key differences between eukaryotes and prokaryotes, which typically have continuous coding sequences. This structure allows eukaryotes to have a much greater genetic complexity and diversity. The process of RNA splicing, which involves the removal of introns and the joining of exons, is a crucial step in gene expression in eukaryotes. It not only ensures that the correct protein is produced, but also allows for the generation of multiple different proteins from a single gene through alternative splicing. This increases the diversity of proteins that a single gene can produce, contributing to the complexity and adaptability of eukaryotic organisms.