Gene expression: Prokaryotes
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Gene expression is the molecular process by which DNA is converted into a functional product called proteins[1]. The two key steps in the production of proteins is Transcription (DNA to RNA) and Translation (RNA to proteins)[1][2]. The processes are different in prokaryotes and eukaryotes. PROKARYOTIC GENE EXPRESSION Transcription a) Initiation In prokaryotes, like bacteria, the chromosome is a covalently-closed circle. For transcription to occur, the DNA double helix must partially unwind. The unwound region is called the transcription bubble . A holoenzyme (a fully functioning enzyme) and promoter is necessary for the initiation of transcription[3]. Prokaryotic RNA polymerase is the holoenzyme which assembles each time a gene is transcribed, and disassembles once transcription is complete. It is composed of 5 polypeptide subunits. These subunits are α, α, β, β', and σ[3]. α-subunits are used to assemble the polymerase on the DNA β-subunit binds to t