Why have gene expression regulation?
• It simply would fail to have all genes always expressed. • Different points of gene regulation in prokaryotes can be seen in Figure 21.1. • Major types of regulation: • Repressible System: The end product of the system increases, which shuts off transcription of the coding region necessary for such synthesis. For example, if an amino acid concentration increases to a certain level, transcription necessary for that amino acid shuts off. • Inducible System: When a substance is present, genes are expressed, when the substance is gone, genes are no longer expressed. • See Figure 21.2. Some prokaryotic genes code for one gene product. More interestingly, some genes share the same promoter and are expressed by the generation of a single transcript with several different starting places for the synthesis of more than one different protein. These genes are said to belong to a single operon. The basic operon is conceptualized in Figure 21.3.
