着色性干皮病课件.ppt

Xeroderma  Pigmentosum(XP)
着***干皮病
We owe our lives to light from the sun,which provides the energy captured during photosynthesis (光合作用).
But the sun also emits a constant stream of ultraviolet rays that ages and mutates the cells of our skin.
The hazardous effects of the sun are most dramatically illustrated by the rare recessive ic disorder , Xeroderma Pigmentosum(XP) .
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Patients with XP possess a dificient repair system that cannot remove segments of DNA damaged by ultraviolet(紫外线) radiation.
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As a result ,person with XP are extremely sensitive to sunlight
Even very limited exposure to the direct rays of the sun can produce large numbers of dark-pigmented spots on exposed areas of the body and a greatly elevated risk of developing disfiguring and fatal skin cancers.
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The mechanism about XP------nucleotide excision repair deficiency(核苷酸切除修复缺陷)
When subjected to ultraviolet radiation ,adjacent(相邻的) pyrimidines(嘧啶) on a DNA strand have a tendency to interact with one another to form a covalent(共价的) plex.(example as TT---胸腺嘧啶二具体)
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Once TT is formed, ultraviolet radiated DNA will not be repaired correctly.
The replication and the transcription of DNA will be influenced seriously.
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THF II H--- a crucial link between transcription and DNA repair
XPB and XPD are two subunits of THF II H
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nucleotide excision repair
In persons with XP who carry specific mutations in the XPD gene.
XPD gene encodes a subunit of the TFII H required for transcription initiation(起始)
So, Mutat