Promoter (genetics) facts for kids
Top: The gene is turned off. There is no lactose to inhibit the repressor, so the repressor binds to the operator. This stops the RNA polymerase from binding to the promoter and making lactase.
Bottom: The gene is turned on. Lactose inhibits the repressor. This allows the RNA polymerase to bind with the promoter, and express the genes. The genes now synthesize lactase. Eventually, the lactase will digest all of the lactose, until there is none to bind to the repressor. The repressor will then bind to the operator, stopping the manufacture of lactase.
In genetics, a promoter is a section of DNA which starts the transcription of a gene.
Promoters are near the genes they transcribe. They are on the same strand of DNA and are 'upstream'.
Promoters can be about 100–1000 base pairs long.
Overview
For the transcription to take place, the enzyme that makes RNA, known as RNA polymerase, must attach to the DNA near a gene.
Promoters contain specific DNA sequences which give the RNA polymerase a place to bind. Other proteins also help this to happen. Some can also stop it from happening. The whole thing is called "the regulation of gene expression".
- In bacteria
- The promoter is recognized by RNA polymerase and another protein.
- In eukaryotes
- The process is more complicated. At least seven different factors are needed so RNA polymerase II can bind to the promoter.
Promoters are important parts of the DNA. They work with other regulatory regions. Together, they adjust the level of transcription of a gene. So, genes get switched on when they are needed, and switched off when they are not. When they are on, they get adjusted up or down as needed.
Images for kids
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Depiction the phenomenon of interference between tandem promoters. Figure created with BioRender.com
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Ten classes of eukaryotic promoters and their representative DNA Patterns. The representative eukaryotic promoter classes are shown in the following sections: (A) AT-based class, (B) CG-based class, (C) ATCG-compact class, (D) ATCG-balanced class, (E) ATCG-middle class, (F) ATCG-less class, (G) AT-less class, (H) CG-spike class, (I) CG-less class and (J) ATspike class.
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Regulation of transcription in mammals. An active enhancer regulatory region is enabled to interact with the promoter region of its target gene by formation of a chromosome loop. This can initiate messenger RNA (mRNA) synthesis by RNA polymerase II (RNAP II) bound to the promoter at the transcription start site of the gene. The loop is stabilized by one architectural protein anchored to the enhancer and one anchored to the promoter and these proteins are joined to form a dimer (red zigzags). Specific regulatory transcription factors bind to DNA sequence motifs on the enhancer. General transcription factors bind to the promoter. When a transcription factor is activated by a signal (here indicated as phosphorylation shown by a small red star on a transcription factor on the enhancer) the enhancer is activated and can now activate its target promoter. The active enhancer is transcribed on each strand of DNA in opposite directions by bound RNAP IIs. Mediator (coactivator) (a complex consisting of about 26 proteins in an interacting structure) communicates regulatory signals from the enhancer DNA-bound transcription factors to the promoter.
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Superposition between promoter distributions from Homo sapiens, Drosophila melanogaster, Oryza sativa and Arabidopsis thaliana. Red color areas represent conserved promoter sequences.
See also
In Spanish: Promotor (genética) para niños
