Lecture 3 Cell Wall PDF

Structure of eukaryotic plant cell A typical eukaryotic plant cell is usually consists of three parts (1) Cell Wall; (2) Cytoplasm and (3) Nucleus. Cytoplasm and nucleus together are called protoplasm. I- Cell Wall: - plant cells have a thick, rigid wall surrounding the plant cell. The chemical and...

Structure of eukaryotic plant cell A typical eukaryotic plant cell is usually consists of three parts (1) Cell Wall; (2) Cytoplasm and (3) Nucleus. Cytoplasm and nucleus together are called protoplasm. I- Cell Wall: - plant cells have a thick, rigid wall surrounding the plant cell. The chemical and physical structure of the cell wall varies from plant group to other plant group and from cell to cell. This layer mainly made up from cellulose and hemicellulose, gives the cell most of its support and structure and serves a variety of functions, from protecting the cell to regulating the life cycle of the plant organism. The cell wall also bonds with other cell walls to form the structure of the plant. In a typical tissue from an annual and or perennial, the cell wall consist of three distinct layers; the middle lamella, the primary wall and the secondary wall.  Cell wall The thickness of plant cells various in relation to age and cell type. The cell walls is a rigid and protective layer around the PM. Cell wall is complex in nature. The cell wall of plant cells are composed of carbohydrate known as cellulose , beside the cellulose various chemical substances as hemicellulose, pectin, cutin, lignin, and chitin occur singly or along with the cellulose. Also the cell wall contains certain minerals as Ca and Mg in the form of carbonate or silicates.  A cell wall is a rigid, permeable and semi-permeable protective layer in some cell types. This outer covering is located next to the cell membrane (plasma membrane) in most plant cells, fungi, bacteria, algae, and some archaea. Animal cells however, do not have a cell wall. The cell wall has many important functions in a cell including protection, structure, and support. Cell wall composition varies depending on the organism. In plants, the cell wall is composed mainly of strong fibers of the carbohydrate polymer termed cellulose. Cellulose is the major component of cotton fiber and wood, and it is used in paper production. Bacterial cell walls are composed of a sugar and amino acid polymer called peptidoglycan. The main components of fungal cell walls are chitin, glucans, and proteins.  Plant Cell Wall Structure The plant cell wall is multi-layered and consists of up to three sections. From the outermost layer of the cell wall, these layers are identified as the middle lamella, primary cell wall, and secondary cell wall. While all plant cells have a middle lamella and primary cell wall, not all have a secondary cell wall. Middle lamella: This outer cell wall layer contains polysaccharides called pectin. Pectin aid in cell adhesion by helping the cell walls of adjacent cells to bind to one another. During the last stage of mitosis (telophase) , microtubules in the cytoplasm migrate toward the equatorial region of the cell. The microtubules are a part of the system called phragmoplast that forms between the daughter nuclei. At the early stages of the cell division or cytokinesis , small droplets or vesicles become oriented at the equator of the original mother cell along the phragmoplast and fuse to form cell plate  Cell wall Primary cell wall: This layer is formed between the middle lamella and plasma membrane in growing plant cells. It is primarily composed of cellulose microfibrils contained within a gel-like matrix of hemicellulose fibers and pectin polysaccharides. The primary cell wall provides the strength and flexibility needed to allow for cell growth.  Cell wall Secondary cell wall: Sec. cell wall is thick and lies near the plasma membrane. The cell possessing sec. wall are frequently without protoplast at maturity. Ex. Tracheid, Vessel elements and certain fibers. It is composed of three layers. Their major constituents are cellulose, hemi- cellulose and lignin Tertiary cell wall: In certain plant cells another cell wall beneath the secondary cell wall. Besides the cellulose, the tertiary cell wall consists of another Chemical substance as xylan. Layers of cell wall and plasmodesmata https://www.google.com/search?q=2011+plant+cell+wall+pearson+education +inc+biology&tbm=isch&ved  Cellulose structure Source: https://www.sciencefacts.net/wp-content/uploads/2023/08/Cellulose-Structure.jpg Cellulose structure and Chemical composition Source: https://www.researchgate.net/publication/335267205_Chemical_composition_  Macromolecules (Chemical units) substance Chemical unit Cellulose glucose hemicellulose Arabinose, xylose, mannose , galactose pectin Glucuronic acid and galactronic acid lignin coniferyl Cuticular substances Fatty acid Mineral deposits Ca, Mg, carbonate or silicates  Prokaryotic cell wall Bacterial cell Gram positive of cell wall (Bacillus subtilis) is 15 -20 nm., while gram negative of bacterial cell wall (E. coli) is 7.5 – 12 nm A Bacterial cell under an electron microscope reveals many components, some of which are external to the cell wall and some are internal to the cell wall. Some of the structures are confined only to certain species and some other structures act as the characteristic features of certain species. Structures external to the cell wall include flagella, capsules and sheaths. Structures of internal to the cell include cytoplasmic membrane and all other cytoplasmic inclusions. Cell wall is a very rigid structure which provides support and gives shape to the cell.. Most of the bacteria live in hypotonic environments and tend to take up water due to the variation in the osmotic pressures between the bacterial cells and the existing environment. Hence, the main function of the cell wall is to prevent the cell from expanding and eventually bursting in the hypotonic environments. Bacterial cell has the ability to retain their original shape when subjected to very high pressures, due to the rigidity of the cell wall.  Chemical composition of the bacterial cell wall Cell wall is composed of two polymers, one consisting of saccharide subunits ( two simple sugars)and the other consisting of amino acid subunits (four amino acids). Thus a bacterial cell wall is glycopeptide which is also known as peptidoglycan. The saccharide component of the cell wall has alternating repeating units of two amino sugars. One of these two is NAM (N-Acetyl Muramic acid) and the other is NAG (N- Acetyl glucosamine). Both NAG and NAM form the back bone of the cell wall structure. The amino acids are glutamic, alanine, glycine and lysine. These amino acids form peptide chain which attach to poly saccharide chains Chemical composition of bacterial cell wall, NAM, NAG, Pentaglycine crosslinking, N-acetyl glucosamine, N-acetyl muramic acid.  Bacterial cell wall https://www.studyandscore.com/studymaterial-detail/cell- wall-of-bacteria-structure  Bacterial cell wall https://open.oregonstate.education/generalmicrobiology/chapter/bacteria-cell-walls/  Gram (+) and Gram (-) The chemically and structurally differences between G(+) and G(-) of bacterial cell wall are; Gram Positive Bacteria: The cell wall of gram positive bacteria is smooth. Gram Negative Bacteria: The cell wall of gram negative bacteria is wavy. lipopolysaccharide Teichoic acid lipoprotein glycopeptide glycopeptide (peptidoglycan) Cell membrane Cell membrane Gram (-) Gram (+)  Gram positive and negative bacteria Gram positive bacteria are more susceptible to antibiotics due to the lack of an outer membrane. while gram negative bacteria contain an outer membrane, they are less susceptible to antibiotics. Therefore, gram negative bacteria are more pathogenic compared to gram positive bacteria. The main difference between gram positive and gram negative bacteria is that gram positive bacteria contain a thick peptidoglycan cell wall along with teichoic acid, allowing the bacteria to stain in purple during gram staining whereas gram negative bacteria contain a thin peptidoglycan cell wall with no teichoic acid, allowing the cell wall to stain in pink during counter staining.  Algal cell wall The algal cells wall are differences according to Cyanophyta consists of three layers: inner: cellulose; middle: pectin; outer : hemicellulose Chlorophyta (three layers): Inner : cellulose; middle: pectin ; outer: chitin Baceliariophyta (two layers): Inner: pectin; outer: silica (ex. Diatoms)  Fungal cell wall It only contains one layer of polysaccharides, called chitin. Chitin is a long chain of N-acetylglucose-amine. However, some species of fungi as Mucor, the chitosan is the main component of cell wall. Chitosan is a long chain of unbranched glucose amine  Plant Cell Wall Function A major role of the cell wall is to form a framework for the cell to prevent over expansion. The plant cell wall supports and protects internal structures and organelles. Cellulose fibers, structural proteins, and other polysaccharides help to maintain the shape and form of the cell. Additional functions of the cell wall include: Support: The cell wall provides mechanical strength and support. It also controls the direction of cell growth. Withstand turgor pressure: Turgor pressure is the force exerted against the cell wall as the contents of the cell push the plasma membrane against the cell wall. This pressure helps a plant to remain rigid and erect, but can also cause a cell to rupture.  Plant Cell Wall Function Regulate growth: The cell wall sends signals for the cell to enter the cell cycle in order to divide and grow. Regulate diffusion: The cell wall is porous allowing some substances, including proteins, to pass into the cell while keeping other substances out. Communication: Cells communicate with one another via Plasmodesmata (pores or channels between plant cell walls that allow molecules and communication signals to pass between individual plant cells). Protection: The cell wall provides a barrier to protect against plant viruses and other pathogens. It also helps to prevent water loss. Storage: The cell wall stores carbohydrates for use in plant growth, especially in seeds.