BRAINCAKEPhytochromes
Phytochrome is a blue-green photoreceptor pigment found in small amounts in plant cells. It is a protein attached to a light-absorbing group. Phytochrome exists in two forms that can be converted into each other by light:
- Pr (also written P660) absorbs red light, with a peak at a wavelength of 660 nm.
- Pfr (also written P730) absorbs far-red light, with a peak at 730 nm.
When Pr absorbs red light it is quickly converted into Pfr. When Pfr absorbs far-red light it is quickly converted back into Pr. In the dark, Pfr slowly changes back into Pr.
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Key terms in this lesson
- transcription factor
- A protein that binds to DNA near a gene and helps or prevents RNA polymerase binding to the promoter, switching the gene on or off.
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