Explanation:
When DNA strands are stained with ethidium bromide and viewed under UV radiation, they appear as bright orange bands. This phenomenon is due to the interaction between ethidium bromide and DNA molecules.

1. Ethidium Bromide Staining:
- Ethidium bromide is a fluorescent dye commonly used to stain DNA.
- It has a strong affinity for DNA and intercalates between the base pairs of the DNA double helix.
- This intercalation causes a conformational change in the DNA structure, resulting in an increase in fluorescence.

2. UV Radiation:
- UV radiation is used to excite the ethidium bromide molecules and make them fluoresce.
- When UV light is shone onto the stained DNA gel, the ethidium bromide molecules absorb the UV energy and then emit visible light in the orange range of the spectrum.

3. Visualization of DNA Bands:
- The ethidium bromide molecules intercalated within the DNA strands fluoresce under UV radiation, making them visible as bright orange bands.
- The intensity of the fluorescence corresponds to the amount of DNA present in each band.
- Therefore, the DNA bands can be visually identified and analyzed based on their brightness and position on the gel.

4. Significance of DNA Bands:
- The DNA bands observed on the gel represent different fragments of DNA that have been separated based on their size or other characteristics.
- The gel electrophoresis technique allows the separation of DNA molecules based on their charge and size, resulting in distinct bands on the gel.
- By comparing the sizes of the DNA bands with known DNA markers or other samples, scientists can determine the size of the DNA fragments and analyze genetic information.

Conclusion:
When DNA strands stained with ethidium bromide are viewed under UV radiation, they appear as bright orange bands. This phenomenon is due to the interaction between ethidium bromide and DNA molecules, resulting in fluorescence. The visualization of DNA bands on a gel is an essential technique in molecular biology for analyzing DNA fragments.