The amino acids on the opposite end of the tRNA molecules, lined up in correct sequence, are then bound together in series. Amino acid codons. After AUG inserts the first amino acid, subsequent groups of 3 bases in the messenger RNA are read as units, each specifying a new amino acid. Mutations can occur whenever a base is incorrectly copied during replication. If this mistake is not corrected, one of the two DNA strands will carry the wrong base.
Mutations can also occur as a result of DNA damage.
Every time you spend four hours soaking up rays at the beach, ultraviolet light causes approximately 10 damaged bases in each of your skin cells. Your body does its best to repair this damage, and fortunately manages to correct most of the damage. But over time, we all accumulate mutations that are not corrected. Some DNA changes have no effect at all. Others may have profound effects.