How does protein synthesis take place in a cell?
Protein synthesis is usually broken down into 2 parts in conventional biology: Transcription and translation.
DNA is the genetic code that stores information for synthesizing proteins. During the first stage of protein synthesis, DNA in the nucleus is copied, or transcribed, on to mRNA. The "m" in mRNA stands for messenger, because DNA doesn't leave the nucleus, and since mRNA carries informaton on the DNA strand outside the nucleus, the mRNA is a messenger. Once it has transcribed the DNA, mRNA binds to a ribosome, an organelle in the cell where translation occurs.
Amino Acids and Codons
Proteins are made of combinations of amino acids. mRNA is made up of codons, a sequence of three nucleotide bases, and each codon codes for a specific amino acid. For instance in the chart below, we can see that the codon "AAU" codes for Asp (asparagine). The tRNA can only bind asparagine there, since tRNA would not match with another anticodon on tRNA can only bind to a codon with the right bases: A (adenine) can only bind to U (uracil) and G (guanine) can only bind to C (cytosine).
When an mRNA codon enters the ribosome, a tRNA carries (transfers) amino acids there. See how in the image below, the tRNA with the amino acid Asp (aspartic acid)brings the amino acid, then would proceed to attach the amino acid to the existing chain, right next to Lys (lysine)?
There are lots of codons on each strand of mRNA, which will form a long chain of amino acids called a polypeptide chain, and a protein consists of one or more polypeptide chains. Therefore, in translation, Codons on mRNA are being translated into a sequence of amino acids that forms a polypeptide chain.
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