How to bind Ethidium Bromide in DNA?and what is cause to human?

Answer 1

Ethidium bromide is a positively charged aromatic compound see http://en.wikipedia.org/wiki/Ethidium_bromide
for structure, effect on humans and safety.

It is an intercalator.
"Intercalation is characterized by noncovalent stacking between adjacent basepairs via interaction with p-orbitals of these basepairs (Graves and Velea, 2000) and often combined with hydrogen bonding (Reha et al., 2002)" (from http://www.physik.uni-bielefeld.de/~rros/Paper_pdf/BiophysJ_2005_Sischka.pdf.)

So the ethidium cation goes into the DNA groove and stacks in parallel to the aromatic rings of the DNA base pairs. "Bonding" is through the interaction of the p-orbitals of the aromatic rings but also through interaction of the protonated imino group of ethidium bromide with the phosphate backbobe of DNA(http://www.biophysj.org/cgi/content/full/88/1/404)

Answer 2

Ethidium bromide intercalates into the DNA double stranded structure. A more detailed description can be found easily on the internet. It is a potential carcinogen.