Messenger RNA is processed before it leaves nucleus, during which time the introns are removed. Messenger RNA carries sequence of codons to ribosomes. A transfer RNA molecule bonded to particular amino acid has anticodons paired to mRNA codons. During translation, tRNA molecules and attached amino acids arrive at ribosomes, and sequence of codons of mRNA determines order in which amino acids become incorporated into a protein. The result of a frameshift mutation is frequently a nonfunctional protein.
Point mutation changes a single nucleotide and therefore changes a single specific codon.
They can range in effect depending on the particular codon change. A change from UAC to CAC incorporates histidine instead of tyrosine, a missense mutation. Mutations due to DNA replication errors are rare. DNA polymerase constantly monitors, proofreads new strand against old, and repairs any irregularities, reducing mistakes to one out of every one billion nucleotide pairs replicated. Mutagens are environmental substances that cause mutations.