A) Proteins may be modified by covalent addition of a variety of molecules B) Not all genes are expressed in all cells at the same time C) Many coding genes are transcribe into mRNA which can be alternatively spliced, and those transcripts produce different proteins so the ratio of the number of protein molecules the number of genes is greater than 1. D) The total amount of protein in a cell as measured by mass is always greater than the total amount of DNA.