G proteins are covalently attached to lipid molecules. Phospholipid head groups can be cleaved to form the second messenger IP 3 . DNA is found in mitochondria. Nucleotides such as ATP can be used to make RNA molecules or as an energy source. Covalent attachment of polysaccharides to protein most commonly occurs in the cytosol of the cell.
Polysaccharides are important for adhesion of cells to each other.
Polysaccharides are found on the surface of cells. Actin filaments are weaker than intermediate filaments. Actin filaments are made of actin monomers held together by non-covalent bonds. Movement or polymerization of actin filaments helps drive extensions of the plasma membrane called pseudopodia. The primary structure of a protein is its unique sequence of amino acids.