1-1.5 Gene expression:

Let us now understand the central dogma of life. You now know that most of the genes contain the information needed to make functional molecules called proteins. However, some genes produce other molecule (tRNA, rRNA, microRNA etc) that assist or regulates the protein expression and assembly. These complex events within each cell consist of two main steps: transcription and translation. In prokaryotes where there is no nuclear membrane, both transcription and translation occur in the cytoplasm whereas in eukaryotes, transcription occurs inside the nucleus and the translation occurs in the cytoplasm.

Fig1-1.5: Central dogma of life

1-1.5.1 Events involved in gene expression:

The events involved in genome expression in higher organisms with respect to protein coding genes are discussed below. The genes that give rise to non-coding RNAs are transcribed and processed but are never translated.

• Access to gene: Genes are inaccessible as they are buried deep within the highly packaged chromosomes. The initial step involves a preparative process that opens the chromatin structure and positions of the nucleosome in the region of genome containing active genes.
  
  
• Formation of transcription initiation complex involves the assembly of a set of proteins into a complex that copy DNA into RNA. This is a highly regulated process as the transcription initiation complex must be constructed at the precise position in the genome, adjacent to active genes to form a RNA copy.