molecular basis of inheritance
Regulation of gene expression
It is the metabolic, physiological or environmental conditions that regulate the expression of genes.
Housekeeping or constitutive genes: genes whose products are continuously required by the cell hence they continuously transcribe and translate.
Non-constitutive genes: genes whose products are not continuously required by the cell & if they continuously transcribe and translate there will be a lot of wastage.
- Regulation of expression of such genes is a must.
Genes can be regulated at
- Transcriptional level.
- During processing i.e., splicing.
- Transport of mRNA from the nucleus to the cytoplasm.
- Translational level.
Genes are regulated at the transcriptional level.
There are 2 systems of regulations:
- An inducible system and a repressible system.
- In the inducible system, an addition of a substance induces transcription of certain genes. It produces catabolic enzymes. It is always OFF. E.g., lac operon.
- In the repressible system, an addition of a substance stops transcription of certain genes. It produces anabolic enzymes. It is always ON. E.g., Tryptophan operon.