Describe the steps involved in protein synthesis in prokaryotes

The mechanism of protein synthesis has been thoroughly investigated in Escherichia coli. In bacterial cell, the protein synthesis takes place on 70s ribosomes.

The process of protein synthesis in E. coli involves the following steps:

1. Transcription:

The partial uncoiling of two DNA strands occurs. This is followed by the production of single stranded mRNA on one of the two DNA strands. The messenger RNA complement is made in accordance with base pairing rules. This is transcription.

The transcription of genetic code of DNA into mRNA is catalysed by the enzyme RNA polymerase. mRNA carries the information in the form of base triplets for the synthesis of a particular protein (Fig. 20.2).

2. The second step involves the separation of mRNA from DNA and then its transfer from nucleus to cytoplasm and final attachment of 5′ end of mRNA with 30s (smaller) sub-unit of ribosome in presence of protein initiation factor. Before the mRNA migrates from nucleus to ribosome in cytoplasm it undergoes process of maturation.

In eukaryotes the newly formed RNA is called heterogenous nuclear RNA (hn RNA). Many of the functional RNA molecules including ?RNA and mRNA in eukaryotes are processed from much longer precursor RNAs which are 5,000 to 50,000 nucleotides long and may be 10 to 100 times longer than the mature functional RNA molecules which are derived from them.

Precursor RNAs are transcripts of split genes which contain both sequences coding for aminoacids (exons) and those not coding for aminoacids (introns) interspersed. The non-coding sequences from the pre-RNAs are cleaved out and coding sequences are spliced together to produce functional mature RNA molecules.

Few of the eukaryotic genes are not split. In prokaryotes some of the RNA molecules are cleavage products of longer pre-RNA.

3. Translation:

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