why does UV light make DNA fragments visible?

Answer 1

UV light only makes DNA fragments visible if they have been stained with a substance that responds to the UV light.

Most commonly, ethidium bromide is used to stain DNA (frequently in agarose gels). Ethidium bromide sits between the bases of a DNA strand. UV light causes the ethidium bromide to be visible allowing the location of the DNA to be seen.

Answer 2

UV light alone does not make DNA visible, but in the presence of Ethidium Bromide, a molecule that tightly binds to DNA and RNA, the Ethidium Bromide fluoresces orange when exposed to UV light.

Answer 3

UV transilluminators have been used for many years for visualizing DNA bands separated on agarose electrophoresis gels. Damage to DNA by the UV light is enough to be detectable after even 5 seconds of exposure and enough to make certain regions unreadable on a sequencing gel within 60 seconds. One solution to avoid exposure of the gel-separated DNA to UV is to run an extra duplicate lane next to the lane with the fragment to be cloned. The duplicate lane is cut out of the gel, stained and visualized on the transilluminator and then used as a marker for where to cut out the band from the lane that is not exposed to UV. A better solution is to use a Dark Reader™ Visible Light Transilluminator from Clare Chemical Company. A Dark Reader uses only visible light, which does not damage DNA and is not harmful to people, and two filters. The gel is first exposed to light that has passed through a blue filter. It filters out all wavelengths except the excitation wavelength of the intercalator dye. Then, the bands are viewed through an orange filter, which only allows the excitation wavelengths to pass through. Sensitivity using SYBR Gold or other dyes exceeds UV light with ethidium bromide. More important, exposure to Dark Reader light does not affect cloning efficiency. In one experiment at EPICENTRE, a 30-second exposure of phage T7 DNA to UV light on a transilluminator decreased the number of transformants obtained using that DNA as an insert by more than two orders of magnitude, but a 5-minute exposure to Dark Reader light had no effect on cloning efficiency. See www.clarechemical.com for more information.

Answer 4

UV light makes DNA fragments visible because these fragments contain chromaphores. Chromaphores are functional groups that contain electrons that get excited when exposed to certain wavelengths of light. The electrons absorb the wavelength, and thus you can see the fragments under UV light. This is more of a chemisty question than a biology question.

Double bonds are great chromophores.

Answer 5

yeah the first person who mentioned Ethidium bromide is right

Answer 6

penetrate into objects making it luminous.