Tag Archives: DNA

Xeroderma Pigmentosum

Xeroderma pigmentosum, or XP, is an autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet (UV) light is deficient. In extreme cases, all exposure to sunlight must be forbidden, no matter how small; as such, individuals with the disease are often colloquially referred to as Children of the Night.  Multiple basal cell carcinomas (basaliomas) and other skin malignancies frequently occur at a young age in those with XP. In fact, metastatic malignant melanoma and squamous cell carcinoma are the two most common causes of death in XP victims. This disease involves both sexes and all races, with an incidence of 1:250,000 and a gene frequency of 1:200. XP is roughly six times more common in Japanese people than in other groups.

Image from Dermamin.com (link)

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Squamous Epithelial Cells

Skin’s top layer is a prototypical “squamous epithelium”: it contains layers of densely packed epithelial cells that form continuous sheets. The sheets stack up on top of each other, and then the whole stack sits on a basement membrane, which supports the epithelial and serves as a source of new cells for growth and regeneration. Epithelia have nerves but no blood vessels.

Epithelia are classified by the shape of the top cells. For the skin epidermis, these cells have a “polygon” shape when viewed from above, and thus, the epidermis is called a “squamous epithelium.” (from Cell.com)

Image from Cell.com  by Tom Deerinck, NCMIR and UCSD

Here cultured epithelial cells are imaged via multiphoton microscopy, illustrating the classic polygon shape of “squamous epithelial cells.” Cell nuclei were stained for DNA using Hoechst 33342 (cyan), the Golgi apparatus expres targeted GFP (green), and actin was stained using fluorescent phalloidin (magenta). (from cell.com)

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First DNA Fingerprint

The first DNA fingerprint. The first three lanes contain DNA from a woman, her mother and her father respectively. Lanes 4 – 11 contain DNA from assorted other species including mouse, baboon, lemur, cow, grey seal and tobacco (last lane). The DNA probe used in this experiment detected tandomly repeated short stretches of DNA called minisatellites whose length varies between individuals. (Wellcome Images)

Image credit Alec Jeffreys (link)


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Picture n 51- DNA at X-Ray

X-ray diffraction diagram numbered 51 of the B form of DNA.  The dark cross let Watson and Crick know that the molecule was a double helix.  DNA (DeoxyriboNucleic Acid), the molecule that carries the genetic information, exists in two forms, A and B.  When in the B form, DNA is shielded in a sheath of water and thus, it is relatively free from the influence of neighboring molecules, the X-ray pattern being then, highly informative. (Image by Rosalind Franklin and Raymond Gosling, 1951. Caption adapted from Raquel Goncalves Maia, CFCUL)

Source: Watson, JD & Crick, FHC, Molecular Structure of Deoxypentose Nucleic Acids, Nature, Vol 171, pp 738-739, 25 April 1953

Link to different version of photo (here)

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