Which of the following amino acids is most likely to disrupt an \alpha -helix?
Which of the following amino acids is most likely to disrupt an-helix?
Select an option to attempt
Correct Answer: Option D
Explanation
Phytochrome A (phyA) is the most abundant phytochrome in dark-grown (etiolated, skotomorphogenic) seedlings, accumulating to very high levels in darkness (constitutively expressed). Upon light exposure, phyA undergoes photoconversion from Pr (red-absorbing, 660 nm peak) to Pfr (far-red absorbing, 730 nm peak). Pfr-phyA is rapidly ubiquitinated by COP1/SPA E3 ligase and degraded via the 26S proteasome (light-labile). This rapid light-induced degradation is why phyA mediates VLFR (Very Low Fluence Response) and HIR (High Irradiance Response) rather than the reversible R/FR responses mediated by light-stable phyB. phyA is essential for de-etiolation responses (hypocotyl elongation inhibition, cotyledon opening, chloroplast development).