 Proteins are the chief actors within the cell , said to be carrying out the duties specified by the information encoded in genes . With the exception of certain types of RNA , most other biological molecules are relatively inert elements upon which proteins act . Proteins make up half the dry weight of an <unk> coli cell , whereas other macromolecules such as DNA and RNA make up only 3 % and 20 % , respectively . The set of proteins expressed in a particular cell or cell type is known as its <unk> . 
