Cells control which genes are expressed and how much protein is made. This control can happen at several stages between a gene and its active protein.1. Before transcription: chromatin structure
DNA in eukaryotes is wound around histone proteins. If the DNA is tightly packed, RNA polymerase cannot reach the gene and it is not transcribed. Chemical changes to DNA and histones, called epigenetic modifications, loosen or tighten the packing.2. Transcription
Proteins called transcription factors bind to DNA near a gene and either help or prevent RNA polymerase binding to the promoter. This is the main way genes are switched on and off.3. After transcription
The pre-mRNA is processed by RNA splicing. The same pre-mRNA can be spliced in different ways to produce different mRNAs, so one gene can code for several proteins.4. Translation
Small RNA molecules, such as siRNA, can bind to a specific mRNA and cause it to be broken down before it is translated. This is called RNA interference.5. After translation
Some proteins are made in an inactive form and must be activated, for example by adding a phosphate group or by cutting the polypeptide. Many hormones work through second messengers such as cAMP, which activate enzymes called protein kinases.Control at the start (transcription) saves the most energy and materials, while control after translation allows the fastest response because the protein is already made.
DNA in eukaryotes is wound around histone proteins. If the DNA is tightly packed, RNA polymerase cannot reach the gene and it is not transcribed. Chemical changes to DNA and histones, called epigenetic modifications, loosen or tighten the packing.2. Transcription
Proteins called transcription factors bind to DNA near a gene and either help or prevent RNA polymerase binding to the promoter. This is the main way genes are switched on and off.3. After transcription
The pre-mRNA is processed by RNA splicing. The same pre-mRNA can be spliced in different ways to produce different mRNAs, so one gene can code for several proteins.4. Translation
Small RNA molecules, such as siRNA, can bind to a specific mRNA and cause it to be broken down before it is translated. This is called RNA interference.5. After translation
Some proteins are made in an inactive form and must be activated, for example by adding a phosphate group or by cutting the polypeptide. Many hormones work through second messengers such as cAMP, which activate enzymes called protein kinases.Control at the start (transcription) saves the most energy and materials, while control after translation allows the fastest response because the protein is already made.