In this context, Monomer refers to the basic building blocks from which all biopolymers are made - these would be the twenty amino acids used in the construction of proteins, the four nucleotides from which DNA and RNA are constructed, and, although they are not of specific reference here, the sugars that serve as building blocks for the complex carbohydrates that go into the cell wall and serve to store energy in the cell. Lipids are another category, and although we do not strictly refer to the fatty acids as building blocks, the subunits are an absolute requisite for the formation of membranes..