Dna Translation
DNA translation is the formation of a protein molecule using the coded instructions present within the deoxyribonucleic acid (DNA) molecule. The first stage of the process is called transcription and involves the production of a molecule of single-stranded ribonucleic acid called messenger RNA (mRNA) from the DNA template. This molecule is transferred from the nucleus to the ribosomes, which are the site of the protein synthesis. Translation starts at one end of the mRNA and proceeds much like the reading of a magnetic tape in a cassette recorder. As the mRNA passes through the ribosome, every codon (set of three bases) is read, and each codon codes for a specific amino acid. These amino acids are brought together and joined to give a chain of amino acids, a polypeptide. The amino acids are brought to the ribosomes by another molecule of RNA, transfer RNA (tRNA). As the amino acids are joined to each other, hydrogen bonds start to form between amino acids within the chain, giving a three dimensional structure to the protein. As the mRNA emerges from the first ribosome, it is quickly attached to a second so the whole process of translation commences again before the first molecule of protein is produced. As soon as the mRNA leaves the first ribosome, that ribosome is ready to start reading another molecule of mRNA. These two processes allow for a fast production of the gene product.
Within the triplet code of the codons, certain sequences code for a start signal that tells the ribosome when to start manufacturing the polypeptide chain. Similarly, there are also stop signals that tell the ribosome when to stop manufacturing the chain of amino acids. These stop signals are sometimes referred to as nonsense codons because they do not code for any amino acids and the mRNA basically falls off the ribosome because there is nothing to add to it.
Before the mRNA is read and translated, certain pieces of the message are removed or excised. These sections of DNA are the nonsense coding sequences that interrupt the DNA /RNA and carry no useful information for the manufacture of proteins. They are called introns. Only the coding parts of the DNA, called the exons, are read and translated. This again speeds up the process of the production of the gene product.
Translation is a fast and efficient process that can yield a large amount of protein in a very short time. The whole process can be brought to a halt in some instances by a build up of the product; in other words, the process can be self-limiting.
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