Summary

1. During protein synthesis, the genetic code in an mRNA is translated into a sequence of amino acids. An amino acid attaches to the 3' end of a tRNA to form an aminoacyl tRNA. Protein synthesis takes place on the ribosome, that binds both to mRNA and tRNA. It has two tRNA binding sites, the P site and the A site.

2. Initiation of protein synthesis in bacteria involves the binding of the 30S ribosomal subunit to the mRNA. tRNAfmet binds to the initiation codon, and then the 50S ribosomal subunit attaches and the 70S initiation complex is formed.

3. Protein synthesis begins when a second aminoacyl tRNA occupies the A site. Each incoming amino acid is specified by the codon on the mRNA. The anticodon on the tRNA hydrogen bonds to the codon, thus positioning the amino acid on the ribosome.

A peptide bond is formed, by peptidyl transferase, between the amino acids in the P and A sites. The newly synthesized peptide occupies the P site, and another amino acid is brought into the A site. This process of elongation requires a number of proteins (elongation factors); as it continues, the peptide chain grows. When a stop codon is reached, the polypeptide chain is released with the help of proteins known as release factors.

4. More than one ribosome can attach to an mRNA. This forms a polyribosome, and many protein molecules can be made simultaneously from the same mRNA.

5. Many antibiotics fight disease because they inhibit particular steps in protein synthesis.

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