When a virus injects its genome into a cell, the molecule is treated the same as if the cell had created it. The ribosomes of a cell are used by the virus to create proteins needed for it to replicate its genome and encapsulate itself so it can leave the cell. A virus is a small strand of DNA or RNA that replicates by hijacking a cell’s normal machinery, including ribosomes. Viruses have taken advantage of this fact. As soon as a tRNA has bound to an mRNA, they attach with the help of various other proteins, and the process of protein synthesis is initiated. Short proteins, of only a few hundred amino acids, can be synthesized in minutes. Given that the largest known protein, titin, is around 30,000 amino acids, it only takes a ribosome 2-3 hours to synthesize. On average, ribosomes can add 3-5 amino acids per second to a protein chain. That is a lot of protein that must be synthesized, which is why the ribosome has evolved to be an efficient and speedy machine. An average cell can have 10,000 different proteins, with on average a million copies of each. Per cell weigh, proteins account for about 20 percent. Ribosomes create all of these proteins that cells need, which is a lot. Other proteins are formed directly in the cytosol where they can start acting as catalysts for various reactions. A ribosome attached to the endoplasmic reticulum, for example, will deposit the newly formed protein inside, where it can be further modified and folded properly. This process of synthesizing new protein is pictured in the image below:ĭifferent proteins require different modifications and transport to various areas of the cell before they can function. Special proteins will detach the string of amino acids from the last tRNA, and the protein will be released. Eventually, the mRNA will present a codon to the ribosome that means “stop”. The used tRNA is released back into the cytosol so it can bind to another amino acid. The ribosome acts as a large catalyst, forming peptide bonds between amino acids. Recognizing the structure of the mRNA bound to a tRNA, the two subunits of the ribosome (discussed below) can combine to start synthesizing protein from the mRNA strand. Depending on the protein being built, the next amino acid could be any one of the twenty. This particular tRNA carries a methionine amino acid. A special RNA molecule that can bind to amino acids, known as a transfer RNA or tRNA, recognizes this sequence and binds to it. This stands for the sequence of nucleic bases: adenine, uracil, and guanine, respectively. The codon that starts all proteins is “AUG”. All life on Earth uses the same 20 amino acids, and the codons used to call for those amino acids are nearly universal. Each codon specifies a specific amino acid. #Initiater definition seriesThe base pairs are “read” in series of threes, making up codons.
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