A common and important statement of the cell theory is that "all living organsims are composed by cells", on other words "cells are abel to make new organisms".
I'd say the cytoplasm, but remember, a simple but more precise answer to this question would be "mitochondria".
Many times we say it occurs in the cytoplasm, only because the cytoplasm holds all the organelles that take part in the metabolic process, so it's basically a way of generalising.
Answer: A missense mutation changes the identity of a codon from one amino acid to another, resulting in a change to the protein primary structure. A silent mutation occurs when a mutation does not change the amino acid coded for by that codon.