Plant Cell Wall PDF

PLANT CELL WALL Dr Suma Sarojini Mission Vision Core Values Christ University is a nurturing ground for an Excellence and Service Faith in God | Moral Uprightness...

PLANT CELL WALL Dr Suma Sarojini Mission Vision Core Values Christ University is a nurturing ground for an Excellence and Service Faith in God | Moral Uprightness individual’s holistic development to make effective Love of Fellow Beings | Social contribution to the society in a dynamic environment Responsibility | Pursuit of Excellence  Christ University Plant Cell wall Primary cell wall is composed of the polysaccharides cellulose, hemicelluloses and pectin. Other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Secondary cell wall is a thicker additional layer of cellulose which increases wall rigidity. Excellence and Service  Christ University Cell wall layers Excellence and Service Primary cell wall Secondary Cell wall The secondary cell wall consists primarily of cellulose, along with other polysaccharides, lignin, and glycoprotein. It sometimes consists of three distinct layers - S1, S2 and S3 - where the direction of the cellulose microfibrils differs between the layers  Middle lamella The middle lamella is a pectin layer which cements the cell walls of two adjoining plant cells together. It is the first formed layer which is deposited at the time of cytokinesis. The cell plate that is formed during cell division itself develops into middle lamella or lamellum. Made up of mainly Ca and Mg pectates apart from galactose, xylose and arabinose.  Christ University Plant Cell wall Excellence and Service  Christ University PLANT CELL WALL COMPOSITION 1. Cellulose Cellulose is a complex carbohydrate and consists of thousands of glucose monomers that form long chains. These chains come together and form cellulose microfibrils, which are several nanometers in diameter. The microfibrils help control the growth of the cell by limiting or allowing its expansion. Excellence and Service  Christ University Excellence and Service  Christ University Role of Calcium in cell wall Excellence and Service  Christ University Calcium pectate in the middle lamella is required for holding together the cellulose microfibrils Excellence and Service  Christ University 2. Hemicellulose Hemicelluloses are heteropolymeric polysaccharides (xylose, mannose, arabinose, glucuronic acid galacturonic acid etc) Structural comparison to cellulose Hemicelluloses consist of shorter chains – 500–3,000 sugar units. In contrast, 7,000–15,000 glucose molecules comprise each polymer of cellulose. Hemicellulose may be branched polymers, while cellulose is unbranched. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicelluloses have random, amorphous structure with little strength Excellence and Service  Christ University 3. Pectin It is a mixture of polysaccharides rich in negatively charged carboxyl groups that combine with Calcium ions. Pectin act as a cement and binds cells together. Cellulose and pectin are approx in equal amounts in the primary cell wall. Middle lamella is rich in pectin. Main component is galacturonic acid, a sugar acid derived from galactose Homo and heterogalacturonans (Rhamno, xylo , arabino etc) During fruit ripening, pectin is broken down and fruit becomes softer as middle lamellae breaks down and cells get separated Occurs in the abscission zone of the petioles of deciduous plants at leaf fall Note: Because of its ability to form a thick gel-like solution, pectin is used commercially in the preparation of jellies, jams, and marmalades. Its thickening properties also make it useful in the confectionery, pharmaceutical, and textile industries. Excellence and Service  Christ University Turgor Pressure One of the main reasons for having a wall in a plant cell is that it can withstand turgor pressure, and this is where cellulose plays a crucial role. Turgor pressure is a force created by the inside of the cell pushing out. Cellulose microfibrils form a matrix with the proteins, hemicelluloses and pectins to provide the strong framework that can resist turgor pressure. Both hemicelluloses and pectins are branched polysaccharides. Hemicelluloses have hydrogen bonds connecting them to the cellulose microfibrils, while pectins trap water molecules to create a gel. Hemicelluloses increase the strength of the matrix, and pectins help prevent compression. Excellence and Service  Christ University How to separate cell organelles? Excellence and Service  16 Cell Fractionation, and Differential Centrifugation Cell fractionation is the breaking apart of cellular components Differential centrifugation: Allows separation of cell parts Separated out by size & density Works like spin cycle of washer The faster the machine spins, the smaller the parts that settled out  Christ University 17 Grind Cell Fractionation, and cells Differential Centrifugation Then Then centrifuge centrifuge Centrifuge longer even longer @ 600 g @ 15,000 g @ 100,000 g Sediment Sediment Sediment Soluble contains contains contains portion of nuclei mitochondria, ribosomes, cytoplasm. lysosomes ER No sediment Excellence and Service  Christ University Asynchronous activity Ribosomes - Structure, types, subunits, functions, antibiotics disrupting its function, any interesting extra information Excellence and Service