A plant's primary cell wall comprises pectic compounds, glycoproteins and hemicellulose. These components are surrounded by a gel-like matrix where a tough network of cellulose microfibrils are firmly set.
The pectic compounds are composed of pectic acid and pectin. Pectic acid, which is characterized by its high solubility, consists of around 100 repeating units of galacturonic acid monomers. Pectin is a longer chain than pectic acid, with around 200 bonded monomers. It is also less soluble, although pectin readily dissolves in hot water.
Glycoproteins are structural proteins that contain carbohydrate links on some amino acids, particularly hydroxyproline, proline and lysine. Hemicellulose is a type of complex carbohydrate made up of several saccharides, including mannose, arabinose and xylose.