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mRNA, or messenger RNA, is a type of RNA molecule functioning to carry genetic information from DNA to ribosomes. The information as a transcript is translated by ribosomes into a protein.
mRNA basically is a linear sequence of nucleotides (the building blocks of RNA). They carry the triplet codes that are used to encode the amino acid sequence of a protein. mRNAs are the information bridge between the genetic information stored in DNA and the final protein product.
Structure of mRNA
The linear structure of mRNA consists of a sequence of nucleotides or the building blocks of RNA. The sequence is determined by the genetic information in DNA. The information in RNA is read in group of three nucleotides, called as codons. Each codon encode a specific amino acid. However, this code has to be first encoded as a RNA transcript in the form of mRNA.
A mRNA contains thousands of such codons that can code for an amino acid sequence – the backbone of a protein. The linear structure of mRNA also contain the regulatory elements for transcription such as the start (AUG) and stop codons (UAA, UGA, UAG), that determine where translation of the mRNA into a protein begins and ends. The structure of mRNA can be modified by post-transcriptional processes termed as splicing, which might affect the final amino acid sequence.
Parts in mRNA
A fully transcribed mRNA has the following parts
- 5′ untranslated region (5′ UTR): The segment of mRNA located at the 5′ (five prime) end of the mRNA molecule. It does not encode for any amino acid but contain regulatory elements that control the translation of the mRNA into a protein. The length of 5′ untranslated region (UTR) of messenger RNA (mRNA) might can vary greatly between different genes and species. In majority of the cases, the 5′ UTR is a few nucleotides in length. In others it may be several hundred nucleotides long.
- Coding Region: This is the segment of mRNA that contains the codons, or groups of three nucleotides that encode the amino acid sequence of the final protein. The coding region in messenger RNA (mRNA) contains the information necessary to transcribe the sequence of amino acids that make up a protein. The patch of mRNA between the start codons (AUG) and the stop codons (UAA, UGA and UAG) is called the open reading frame (ORF). This sequence of nucleotides in the coding region exactly determines the sequence of amino acids in the protein molecule. , and therefore, the function and properties of the protein.
- 3′ untranslated region (3′ UTR): The untranslated segment of mRNA at the 3′ (three prime) end of the molecule. It also does not encode for any amino acids in the final protein. The 3′ UTR might also contain regulatory elements that control the stability of the mRNA.
- Introns: Introns are non-coding regions that are located inside genes and are translated into messenger RNA (mRNA). They disrupt a gene’s coding sequence and are translated into the pre-mRNA molecule alongside the exons (the coding sequences). Splicing is a process that involves the removal of intron sequences and the combining of exons to remove introns from pre-mRNA. The resulting spliced mRNA molecule has only the exons and is ready for protein translation. Introns serve an important role in gene expression regulation by permitting alternative splicing, which results in various mRNAs from the same gene and, thus, different proteins with diverse functions.
- Exons: Exons are gene segments that are transcribed into messenger RNA (mRNA) before being translated into protein. They contain the coding sequence that specifies the amino acid sequence of a protein. In most cases, exons are separated by non-coding regions known as introns. The introns are spliced out of the pre-mRNA molecule during gene production, and the exons are linked together to produce the final mRNA molecule. Ribosomes then transfer the mRNA from the nucleus to the cytoplasm, where it is translated into protein. The number, size, and order of exons can differ between genes and species, contributing to the variety of proteins that can be produced from a same genome.