How does mRNA code for a particular tRNA?

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During translation, the information encoded in mRNA is read and used by the ribosome to make a protein. mRNA is made up of a single strand of nucleotides carrying nitrogenous bases that can be either adenine, uracil, cytosine or guanine. Even though mRNA is single stranded, if given the chance,...

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During translation, the information encoded in mRNA is read and used by the ribosome to make a protein. mRNA is made up of a single strand of nucleotides carrying nitrogenous bases that can be either adenine, uracil, cytosine or guanine. Even though mRNA is single stranded, if given the chance, adenine with bind with uracil, and cytosine will bind with guanine. This specific pairing is important when converting this message into a protein product. 

tRNA stands for transfer RNA, and its role is to transfer amino acids to the ribosome to be linked together to make a protein. As is suggested by its name, tRNA is made up of single stranded RNA as well, but it is folded in such a way that it has an end that attaches to an amino acid and an end that has a series of 3 nucleotides that will match up with the mRNA.

The ribosome reads the mRNA in groups of 3 bases called codons. A tRNA will only be brought in to use its amino acid if its series of 3 bases, called an anti-codon, matches up with the mRNA codon. 

Let's start at the beginning of making a protein. The start codon for every protein is AUG. The ribosome begins reading the mRNA and looks for the sequence AUG. Once it finds it, it needs a tRNA with an anti-codon of UAC to match up with AUG. Remember that adenine binds with uracil and cytosine binds with guanine. This matching tRNA is carrying the amino acid methionine, because that is coded for by AUG. The ribosome will then move to the next codon, which let's say is CCA. It brings in a tRNA with the anti-codon GGU to match up. This tRNA is carrying the amino acid proline, and the ribosome will join the proline to the methionine, beginning the chain of amino acids that will become the protein. The ribosome will continue moving along the mRNA, bringing in the correct tRNAs, and joining amino acids together until it reaches a stop codon on the mRNA. There are three different stop codons: UGA, UAA, and UAG. At this point, the ribosome will release from the mRNA and release the protein as well. 

In short, the codon on the mRNA determines which tRNA will be able to bind to it because of the pairing rules. You can use a genetic code such as the image below to determine which amino acids are coded for by the mRNA.

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