Re: How does UV light affect DNA?

Ultraviolet light affects DNA by cauing Pyrimidine dimers to form. Pyrimidine dimers are formed from two pyrimidine bases next to each other on the DNA strand become covalently linked (i.e. chemically bonded to one another). This dimer disrupts the normal replication of the DNA or transcription to make protein. Luckily, cells can usually repair themselves by a rather complex mechanism involving several enzyme groups, because the second strand of DNA is unaffected by the mutation, so replacement DNA can be synthesised... usually.

For more detail, look in

STRYER, L. (1988). BIOCHEMISTRY, 3RD EDITION. WH.FREEMAN AND CO., NEW YORK.
IT'S SOMEWHERE AROUND PAGE 700, FROM MEMORY!

Hope this is enough detail - i'm afraid i'm not enough of a biochemist to help further!

James