6.2 Translation

Before we discuss about translation, we would first review what is a transfer RNA (tRNA). tRNA is a single strand of polynucleotide that has a hair-pin loop structure (see below).

At one end it has a triplet of base known as anti-codon. The anti-codon will bind to mRNA will complementary base pairing. At the other end, it will bind to a specific amino acid.

It is important to note that each tRNA will bind to one specific amino acid.

Above: Seven tRNA attached to their specific amino acid. However tRNA with anti-codon TAC will only be bound to methionine and not other amino acid.

Process of translation

Translation occurs at the ribosome found in the cell cytoplasm. Ribosome will bind to the mRNA. The ribosome can only cover two codons at any one time.

• The first codon on mRNA is AUG so the tRNA with anti-codon TAC will bind to the first codon by complementary base pairing. tRNA with anti-codon TAC will be attached to methionine.

• The second codon on mRNA is UUA so the tRNA with anti-codon AAU will bind to the second codon by complementary base pairing. tRNA with anti-codon AAU will be attached to leucine.

• A peptide bond is formed between the two amino acids methionine and leucine.

• The ribosome moves to the next codon. The first tRNA is removed.

• The third tRNA with anti-codon CGG will bind to the third codon GCC by complementary base pairing. The third tRNA is bound to alanine.

• A peptide bond is formed between leucine and alanine.

• The process continues until the ribosome reaches the last codon.

• The last codon is the stop codon. Ribosome will release the mRNA. The free tRNA will be removed.

• The polypeptide chain will then fold to form a protein.