Because is it less hazardous while still having good results
Studies are inconclusive that ethidium bromide, an inhibitor for cell growth, is not shown to be toxic in humans, but the metabolites may exude mutagenic characteristics.
Ethidium bromide binds with DNA and slips in between its hydrophobic base pairs and stretches the DNA fragment, removing water molecules from the ethidium cation. The result of this dehydrogenation is an increase in fluorescence of the ethidium (as well as the cell).
Ethidium bromide is a chemical that is able to intercalate (fit between the bases) between the bases of double stranded DNA strands
Ethidium bromide is a mutagen that can cause changes in DNA, potentially leading to harmful mutations. It is also a possible carcinogen and can be harmful if handled improperly, such as through direct skin contact or inhaling its fumes. Proper safety precautions, such as wearing protective gear and working in a well-ventilated area, should always be taken when using ethidium bromide.
The purpose of ethidium bromide is as an intercalating agent commonly used as a fluorescent tag (nucleic acid stain) in molecular biology laboratories for techniques such as agarose gel electrophoresis. When exposed to ultraviolet light, it will fluoresce with an orange color, intensifying almost 20-fold after binding to DNA. Hence it is useful in visualizing DNA. Unfortunately, ethidium bromide does not distinguish between what DNA it binds to, whether it be ours or our sample's. Hence ethidium bromide is a mutagen, suspected carcinogen and at high concentrations is irritating to the eyes, skin, mucous membranes and upper respiratory tract. Ethidium bromide acts as a mutagen because it intercalates into double stranded DNA, thereby deforming the molecule. This is believed to block or trip biological processes occurring on DNA, like DNA replication and transcription.
S. Chaudhuri has written: 'Radiation studies on ethidium bromide'
Ethidium bromide is commonly used for staining native PAGE gels where proteins are kept in their native state. However, ethidium bromide is typically used for staining DNA in denaturing PAGE gels as it binds to DNA molecules specifically, providing better visualization compared to proteins in native gels. This is why alternative stains such as Coomassie blue or silver staining are typically used for proteins in non-denaturing PAGE gels.
Ethidium bromide is an intercalator, meaning it inserts itself between the base pairs of DNA. Linear DNA pieces like the genomic DNA fragments bind more ethidium bromide than the circular plasmid DNA. The solution is placed into a tube that is spun extremely fast (roughly 50,000 revolutions per minute) in an ultracentrifuge for about a day. During this time the cesium chloride forms a gradient of lower density at the top of the tube and higher density at the bottom. The genomic and plasmid DNA form tight bands in this gradient. Since the plasmid DNA binds less ethidium bromide it is more dense and is located lower in the tube than the genomic DNA. RNA forms a separate band at the bottom of the tube. These three bands can be visualized by UV light.
Ethidium bromide is added to agarose gel electrophoresis to visualize nucleic acids, such as DNA and RNA, after they have been separated by size. It intercalates between the base pairs of nucleic acids and fluoresces under ultraviolet (UV) light, allowing for the detection of bands in the gel. This enables researchers to assess the quantity and integrity of the nucleic acids present in the sample. However, it is important to handle ethidium bromide with care due to its mutagenic properties.
Due to fluorescence, it absorbs UV and emits Orange light.. It is due to a phenyl group.. EtBr fluoresces even when not bound to DNA but its fluorescence increases 20 times when in bound state as hydrophobic environment between base pairs force dissociation of water bound to ethidium cation. Note: Water quenches fluorescence highly.
when ethidium ion intercalates between two dna base pairs in a circular dna it causes the dna to unwind by 26 degrees, thereby decreasing twist and increasing writhe. in a circular dna which is negatively supercoiled, if ethidium is added it will become relaxed and if more ethidium is added dna becomes positively supercoiled
Common stains used after DNA electrophoresis include ethidium bromide, SYBR Safe, and GelRed. These stains intercalate with DNA and allow visualization under UV light. They are used to detect and analyze DNA fragments separated on the gel.