Two different molecules, belonging to different categories, usually combine together to form conjugated molecules. Carbohydrates may combine with proteins to from glycoprotein or with lipids to form glycolipids. Most of the cellular secretions are glycoprotein in nature. Both glycoprotein’s and glycolipids are integral structural components of plasma membranes. Lipoprotein formed by combination of lipids and proteins are basic structural framework of all types of membranes in the cells.
Nucleic acids have special affinity for basic proteins. They are combined together to form nucleoproteins. The nucleohistones are present in chromosomes. These conjugated proteins are not only of structural, but also are of functional significance. They play an important role in regulation of gene expression.