Organisms do not want all of their genes to be expressed all of the time. This would use up way too many resources and energy. So, cells have evolved mechanisms for controlling gene expression. This lesson describes many types of gene regulation.
Gene regulation is the informal term used to describe any mechanism used by a cell to increase or decrease the production of specific gene products (protein or RNA).
Cells can modify their gene expression patterns to trigger developmental pathways, respond to environmental stimuli, or adapt to new food sources. All points of gene expression can be regulated. This includes transcription, RNA processing and transport, translation and post-translational modification of a protein, and mRNA degradation.
Regulation of Transcription
Regulating transcription enables a cell to determine when a gene is transcribed. It also allows a cell to increase or decrease the amount of mRNA generated from each gene. There are five different ways that RNA polymerase (the enzyme that makes RNA from a DNA template) can be affected:1. A cell can change the specificity of RNA polymerase for promoters.
It does this by using specificity factors. These regulatory proteins will make RNA polymerase more or less likely to bind to a promoter. An example is the sigma factors used in prokaryotic transcription.2. Repressor proteins can be used to bind an upstream coding sequence, called an operator, to inhibit the ability of RNA polymerase to transcribe the gene. This causes decreased expression of a gene.3.
Activator proteins, which are the opposite of repressor proteins, can bind to the operator region to increase the attraction of RNA polymerase for the promoter. This action can be direct or indirect but always increases expression of the gene. If indirect, it is likely done by changing the structure of the DNA.4. There are also regulatory regions that lie far upstream to their target gene. These are called enhancer regions.
Binding of an activator to an enhancer causes the DNA to form a loop, which brings the enhancer next to its target gene. This causes increased expression of the target gene.5. When a cell wants to completely turn off expression of a gene it uses silencer regions. When a silence region is bound by transcription factors, the gene is silenced.
This means that there is no expression of the gene.
A newly transcribed RNA is not ready for translation (if it is to be a protein) or as a functional RNA molecule. newly made RNA is called pre-RNA. It needs to be processed in order to become mature RNA. Any enzymes involved in this process can be inhibited, which results in decreased expression of the gene associated with the RNA transcript.
Regulation of Translation & Post-Translational Modifications
Translation can be regulated many different ways.
For example binding of ribosomes to the transcript can be prevented by binding of antisense RNA to the transcript. Ribosomes can only process single-stranded RNA. In addition, there are a large number of RNA binding proteins that can also inhibit translation. Once produced, a protein usually undergoes post-translational modifications. Inhibiting these processes will prevent the formation of a functional protein.
Regulation of mRNA Degradation
The stability of mRNA determines how many proteins can be produced from that transcript. mRNA can be destroyed many different ways.
One example is enzymes that specifically target mRNA and microRNA. Binding of microRNA to mRNA cause the mRNA to become double-stranded. This prevents translation of the transcript and also makes the mRNA a target for enzymes that target double-stranded RNA.
Gene regulation is the informal term used to describe any mechanism used by a cell to increase or decrease the production of specific gene products. All points of gene expression can be regulated. Regulating transcription enables a cell to determine when a gene is transcribed.During transcription, RNA polymerase can be affected to increase, decrease, or stop gene expression.A newly transcribed RNA, or pre-RNA, is not ready for translation or as a functional RNA molecule. It needs to be processed to become mature RNA.
The stability of mRNA determines how many proteins can be produced from that transcript.