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Translation | Protein Synthesis | Step wise | Lecture 9

The genetic code During translation, a cell “reads” the information in a messenger RNA (mRNA) and uses it to build a protein. There are 61 codons for amino acids, and each of them is "read" to specify a certain amino acid out of the 20 commonly found in proteins. One codon, AUG, specifies the amino acid methionine and also acts as a start codon to signal the start of protein construction. There are three more codons that do not specify amino acids. These stop codons, UAA, UAG, and UGA, tell the cell when a polypeptide is complete. All together, this collection of codon-amino acid relationships is called the genetic code, because it lets cells “decode” an mRNA into a chain of amino acids. Translation requires some specialized equipment. • Ribosomes provide a structure in which translation can take place. They also catalyze the reaction that links amino acids to make a new protein. • tRNAs (transfer RNAs) carry amino acids to the ribosome. They act as "bridges," matching a codon in an mRNA with the amino acid it codes for. Structure of the ribosome A ribosome is made up of two basic pieces: a large and a small subunit. A transfer RNA (tRNA) is a special kind of RNA molecule. Its job is to match an mRNA codon with the amino acid it codes for. How does the right amino acid get linked to the right tRNA (making sure that codons are read correctly)? Enzymes called aminoacyl-tRNA synthetases have this very important job. #GeneExpression #GeneticCode #TranslationProcess