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mRNA, or messenger RNA, is a crucial component of the process of gene expression. It is created during transcription, where an enzyme called RNA polymerase reads the DNA sequence and synthesizes a complementary RNA strand. This mRNA strand carries the genetic instructions from the DNA out of the nucleus to the ribosome, the cell's protein factory.
The mRNA consists of exon and intron sequences. Exons code for proteins, whereas introns do not. Before mRNA can be used in the protein synthesis process, it must be processed to remove these non-coding segments, known as introns. This processing transforms the initial mRNA transcript into a mature form that can be translated into a protein.
Key features of mRNA include:

• Single-stranded format made from the DNA template
• Contains codons, sequences of three nucleotides that specify amino acids
• Undergoes processing steps like capping, polyadenylation, and splicing

Introns are sections of RNA that do not code for proteins. They appear in the mRNA after transcription but are not needed in the final mRNA copy used for protein synthesis. These non-coding regions are removed in a process called RNA splicing.
During splicing, the introns are excised and the exons are linked together to form a contiguous coding sequence. This is crucial because only exons are required to build a functional protein. Introns may have regulatory roles, but they must be removed to ensure only relevant coding sequences are utilized.
Important aspects of introns include:

• Are found in the primary mRNA transcript and not in the mature mRNA
• Must be correctly spliced out to prevent errors in protein synthesis
• Can contain sequences that regulate gene expression

Exons are the segments of DNA or RNA that are expressed as proteins. They remain in the mRNA after the introns have been spliced out. During the process of translation, these sequences are read by the ribosome to create proteins, maintaining the order dictated by the DNA template.
The precise removal of introns and retention of exons during RNA splicing is vital for accurate protein synthesis. An error in splicing can lead to faulty proteins that may cause disease.
Key points about exons are:

• Code for amino acids and are translated into proteins
• Are joined seamlessly after introns are removed
• Remain in the final mRNA transcript, ensuring proper gene expression