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What is hemicellulose?
Hemicellulose is a polysaccharide similar to cellulose but consisting of many different sugar building blocks (monomers) in shorter chains than cellulose. It is used as a flexible cell wall support in plants.-Cellulose is made of many repeating sugar units, as many as 15,000; but -hemicellulose is made of only about 500 to 3,000 sugar units.-There are many different kinds of hemicellulose found in plant cell walls. Primary cellular walls have predominatly xyloglucan. Other forms of hemicellulose include glucuronoxylan, arabinoxylan, glucomannan, and galactomannan which are found in primary and secondary plant cell walls.-These molecules are arranged in a less organized waythan regular cellulose and they tend to chemically break apart in acidic or basic conditions.-They are found abundantly in plant collenchyma cells. These cells have a support function, particularly in young plants. They allow the plant to have support but also be flexible, if bent over the plant (or part) can snap back up.-Higher levels of hemicellulose in animal feed is favoredbecause the animals will tend to eat less on their own.
What makes up a plant cell wall?
Composition of Cell Wall:The major Carbohydrates making up the primary (budding) plant cell wall are cellulose, hemicellulose and pectin. The cellulose microfibrils are linked through hemicellulosic chains to form the cellulose-hemicellulose web, which is fixed in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan. In grass cell walls, xyloglucan and pectin are sometimes partially replaced by glucuronarabinoxylan.The outer part of the primary cell wall of the plant epidermis is usually impregnated with cutin and wax, forming a permeability barrier known as the plant cuticle.Secondary cell walls contain a wide range of other compounds that modify their mechanical properties and permeability. The major polymers that make up wood (largely secondary cell walls) include cellulose (35 to 50%), xylan (20 to 35%) and lignin (10 to 25%). The walls of cork cells in the bark of trees are impregnated with suberin, and suberin also forms the permeability barrier in primary roots known as the Casparian strip. Secondary walls - especially in grasses - may also contain microscopic silica crystals, which may strengthen the wall. These silica crystals also ensure the survival of plant by saving them from getting grazed by herbivores.All these compounds working in coordination make the cell wall unbreakable.Cell Walls in Fungi:Fungal cell walls are made of chitin, the same material from which exoskeletons of insects are made, it is a polymer of glucosamine.Cell Walls in Diatoms:Diatomic cell walls are composed of Silicic Acid which is a compound of silicon, oxygen and hydrogen.Bacterial Cell Walls:In Eubacteria, cell walls are of peptidoglycan. In archaeobacteria, A variety of compounds make up cell wall for example Glycoproteins, Psuedopeptidoglycan and Polysaccharides.Check out the related links to see microscopic structure of Cell Wall.
