Overexposure of animals to X-rays is dangerous because X-rays are know to damage DNA. A direct result of this damage is cells with

Six amino acids have side chains that are polar but not charged. these are serine (ser), threonine (thr), cysteine (cys), asparagine (asn), glutamine (gln), and tyrosine (tyr). these amino acids are usually found at the surface of proteins, as discussed in the proteins 2 module.

Could you elaborate?

All of them are man made