Page 96 - The Miracle of Protein

94 THE MIRACLE OF PROTEIN

Special Sites for tRNA
Inside the ribosome, there are special sites for the transfer
RNA called E, P and A sites. There exists a very complex corri-

dor inside the ribosome that enables tRNA to insert itself into
these areas and move from one to the other. The tRNAs carry-
ing the amino acids that to be joined together are kept in sec-
tions P and A. The site close to the transit out from the unit is
section.
Site A is where the tRNA is recognized by the ribosome
and taken inside. After the codon-anticodon matching is com-
pleted, the tRNA slides one-step forward, similar to the move-
ment of a typewriter, until it reaches site P. Here, the amino

acid attached to the tRNA is cleaved and released, then attached
to the new amino acid in the section where peptide bonds are
made. In this way, amino acid chain grows one more link. After
this point, the tRNAs in the sections P and A are moved one
step to the side, so that the process can continue.
Finally, tRNA which has delivered its valuable cargo -the
amino acids- to the ribosome, moves one step along with others

and exits from site E. Owing to the shape of the ribosome and
the perfect coordination of its components, this complex
process takes place both very rapidly and accurately. The small-
est error here will mean the end of life. Indeed, many antibiotics
work by halting protein synthesis in the bacteria ribosome, thus
kills the bacteria, effectively curing bacteria caused disease. All
these processes that take place during the protein synthesis are
carried out extremely rapidly. For example, in many situations,
while the mRNA thread removes the copy from the DNA still

attached to it, the translation process on the other end begins. 26
And hundreds of ribosomes can simultaneously carry out its
production based on the same mRNA strand. In the same way,