How does radiation cause damage in cells?

[madcat8000]

I recently read in a book by a trusted author that most all of the damage done by radiation was into form of its interaction with water therby forming radicals that then proceded to do the damage.
Is this "in general" true and other books that attribute different actions with different forms of radiation were oversimplifing the details?
One memorable example was a microbiology textbook that associated UV radiation with small chincks and dimmers in a chromosome, while stateing that gamma radiation was far more dangerouse as it split the DNA completely into two pieces making the damage nearly unrepairable unless the cell was lucky enough to have a repair molecule working at that spot at that time. Aparently (and logicly) after a few seconds the ends of the DNA hit by gama radiation would be so far apart there would be no way to reconnect them.
However after some reflection the idea that radation does damage directly is a bit silly. Tons of water in a cell, far more likely to hit that imho.

Well thanks for reading this, maybe someone with some physics knowledge can speak authoritatively on this because id really like to know.

 

[Ygggdrasil]

There's probably a mixture of both mechanisms in action and the mechanism likely depends on the specific type of damage as well as the type of radiation.

For UV damage to DNA such as thymine dimers, I think it's likely that the nucleotide bases themselves absorb the UV radiation, which puts them into an excited, unstable chemical state allowing them to react with nearby bases to form dimers. In the case of chromosome breakage due to x-ray and gamma radiation, however, I would agree that the generation of reactive oxygen species is most likely mechanism.

If one wanted to generalize, I think that lower energy radiation (e.g. UV) is more likely to cause damage to biomolecules through direct absorption by the biomolecules whereas higher energy, ionizing radiation (e.g. x-ray and gamma) are more likely to cause damage via exciting/ionizing water molecules.

 

[madcat8000]

Ok I can roll with that. So in general radiation does damage via oxygen radicals but this doesn't preclude that "events" will happen in whitch occasionaly the damage is done directly...and the POV depends on whitch is more important. Oxygen radicals add to the overall stress levels of the cell while in certain mutations it dose appear that there was a direct interaction with radiation. TYVM