DNA contains genes that code for characteristics of an organism. Nucleotides code for amino acids, which determine the structure and function of a cell. Introns are non-coding sections of DNA that must be removed before mRNA can be translated into a protein. snRNPs remove introns, but they are needed for functional RNA molecules. Introns may have a regulatory function and allow genes to evolve without relying on mutation.
Deoxyribonucleic acid, or DNA, contains the basis of the genetic code. Genes are sections of DNA that code for particular characteristics of an organism. Not all parts of the gene are actually part of the genetic code. There are sections of DNA that don’t code for anything, which are called introns.
The genetic code of an organism is determined by the sequence of nucleotides that make up its DNA. Nucleotide triplets code for specific amino acids, which are the building blocks of proteins. The sequence of amino acids determines which protein should be formed within a cell. This in turn determines the structure and function of the cell.
To create a protein from DNA, two processes are undertaken. First, the entire DNA strand is transcribed into messenger RNA or mRNA. At this point, introns, or unnecessary parts of the DNA molecule, are included in the mRNA molecule, which is called the primary transcript. This mRNA molecule is non-functional and must undergo further modification before it can be translated into a protein.
Before leaving the nucleus, large portions of the primary transcript are removed. Often up to two-thirds of the original molecule is cut before a functional mRNA molecule results. The sections of mRNA that survive the removal process are called exons because they are expressed. The portions of the gene that correspond to this functional mRNA are also called exons. Each intermediate section of the primary transcript that is cleaved from the molecule and corresponding region of the gene is an intron.
Removing every single intron from a gene can be a formidable task. Some genes have 50 or more introns throughout their sequence. A single mistake can cause mRNA to fail. It is the job of small nuclear ribonucleoprotein (snRNP) particles to remove introns within genetic sequences. At least four different snRNPs play a role in intron splicing from the primary transcript.
Many experiments have shown that even if introns are removed early in the process, they are needed to make functional RNA molecules. Studies have shown that mRNA transcribed from genes that were artificially produced due to lack of introns often failed to leave the nucleus. Other studies found that mRNA with some introns intact managed to escape into the cytoplasm.
The actual function of introns is unclear. Introns appear to provide a regulatory function to the transcription process. Their greater importance is thought to be that they provide a way for genes to evolve without having to rely on mutation.
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