Question

Describe in detail, translation of an mRNA by a ribosome. Include the function of rRNA and tRNA and associated enzymes or complexes.

Answer 1

Ribosomes are the sites in the cell where protein synthesis takes place. In prokaryotes translation occurs in the cytoplasm and in eukaryotes, occurs mostly in the cytosol.

rRNA is responsible for reading the order of amino acids and linking the amino acids together.These are responsible for the translation of mRNA to proteins.

Steps of Translation:

• Initiation:

Initiation begins when the mRNA, tRNA and the first amino acid all come together within the ribosome. tRNAs are the small non-coding RNA chains that transport amino acid to the ribosome. tRNAs have a site for amino acid attachment and a site called anti codon. True initiation point is the start codon, AUG which is the set of 3 nucleotides which begins the coded sequence of a gene. but mRNA strand remains continuous.The start codon specifies the amino acid Methionine which first enter into the ribosome by attaching to the tRNA that contains the right anticodon.

The anticodon for AUG is UAC according to complementary base pairing.

AUG-UAC

Hence mRNA is attached to tRNA attached to Methionine.

together the pieces form into Initiation complex which initiated to form a protein.

In prokaryotes, few enzymes involved in the translation process.

fMet-tRNA-synthetase attaches N-formal methionine to tRNA-aminoacyl tRNA synthetase-attaches amino acid to tRNA-peptidyl transferase.

• Elongation:

The tRNA transfers an amino acid to the tRNA corresponding to the next codon. The ribosome then translocates to the next mRNA codon to elongate the process thereby forming an amino acid chain.

• Termination:

when a stop codon is reached, ribosome releases polypeptide. After the small and large ribosomal subunits separate from the mRNA, and from each other, each element goes for another round of translation and the cyclic process continues.