The synthesis of proteins is directed by DNA or genetic RNA, where DNA is absent. The basic information for the polypeptide structure is stored in the polynucleotide chain. The base sequence in the codon determines the amino acids sequence in a particular polynucleotide.
In general, there are three views regarding the flow of genetic information and these are one-way, circular or reverse flow of genetic information. The information from nucleic acid to proteins is referred to as central dogma and is widely used to explain how protein synthesis is controlled by nucleic acids.
Three kinds of RNAs mRNA, tRNA and rRNA are produced in a cell; of these mRNA (messenger RNA) is heterogeneous and unstable and constitutes minor percentage of the total cellular RNA.
The mRNA of eukaryotes differs from that of prokaryotes. In the former the mRNA originates in the nucleus and migrates to the cell cytoplasm where it is translated. Eukaryotic mRNA has long life and is highly stable. Though all the RNAs take active part in protein synthesis, it is only mRNA which has the “message” of codon. Further, mRNA and tRNA are highly specific while rRNA has a general function to perform.
For a successful translation to occur following factors are essential:
RNA (mRNA, tRNA, rRNA)
Ribosomes
Amino acids and
ATP, GTP.
Enzymes (e.g. amino-acyl-tRNA synthetase) and
Factors essential for initiation, propagation and termination of protein synthesis.
In protein synthesis following steps are involved (Fig. 4-9, 9A).
1. Transcription
2. Maturation of mRNA
3. Translation.
