Regulation of Gene Expression. Chapter 18. How do Organisms Control the Level of Gene Expression?. Cells must only express genes when needed Gene expression (transcription, translation) takes up large amounts of cellular energy and resources
The lac operon is always off and is turned on by an inducer molecule (allolactose). This is why it is called an inducible operon
The trp operon is always on and is turned off only by end product – tryptophan. This is why it is called a repressible operon.
Linker DNA links one
nucleosome to the next
Bacteria lack histones, although some archea have them