Plasma Membrane - Lecture Note

PLASMA MEMBRANE Different biological function that carry by membrane-bound organelles can found in eukaryotic cells. It is an amphipathic molecules (containing hydrophobic and hydrophilic regions simultaneously) containing a bound glycerol core. Non-glyceride components of lipids such as sphingomyelin and sterols also found in biological membranes. In biological membranes. In plants and algae, galactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol, which lack phosphate groups, are important components of chloroplast membranes and related organelles and are the most abundant lipids in photosynthetic tissues, including higher plants, algae and certain bacteria. The thylakoid plant membrane has the largest lipid component in the form of a non-bilayer formed from monogalactosyl diglyceride (MGDG), and small phospholipids; although this lipid composition is unique, chloroplast thylakoid membranes have been shown to contain a dynamic bilayer lipid matrix as revealed by magnetic resonance and electron microscopy studies. Biological membranes are a form of lipid bilayer in the lamellar phase. The formation of lipid bilayers is an exothermic process when the glycerophospholipids described above are in an aquatic environment. In an aquatic system, the polar heads of lipids align toward the polar aquatic environment, while the hydrophobic tails minimize their contact with water and tend to cluster together, forming vesicles; depending on the lipid concentration, these biophysical interactions can result in the formation of micelles, liposomes, and lipid bilayers.  Cell Membrane Structure The outer part of prokaryotic and eukaryotic is plasma membranes that separates the cell from its surroundin enviroment. Composed of protein lipids and carbohydrates with the composition: protein molecules (50%-70%), phospholipids (25%), cholesterol (13%) ; other lipids (4%), and carbohydrates (3%), a little glycolipid, water and ions.Therefore the plasma membrane is selectively permeable. Selectively permeable means it can only enter or pass through certain molecules. The structure of the plasma membrane is also equipped with protein structures: Attached (peripheral/extrinsic) proteins that only attach to the membrane surface and do not penetrate the membrane. Works as a protein transporting materials in the opposite direction to actual diffusion. Extrinsic proteins associate with the outer surface of the membrane. Embedded (integral/intrinsic) proteins that protrude completely from the membrane, have both hydrophobic and hydrophilic parts. Integral proteins form structural channels (or pores) through which water-soluble materials, especially ions, can diffuse between extracellular and intracellular fluids.  Plasma Membrane Function Cells have a material storage system inside the cell that is similar to a container in the form of a plasma membrane, a thin layer that cannot be observed with a light microscope. Intracellular fluid differ from the external enviromnent for example in terms of ion content. The compartmentation system can occur because of the plasma membrane system (cell membrane) which is able to prevent the process of diffusion or movement of certain molecules from the inside to the outside or vice versa from the outside into the membrane system. This compartmentation allows each organelle to have a specific function. Processes of a cell is depend on functions, properties, structure and trasnport system of plasma membranes. Plasma membrane function is to enclose cells, limit cell expansion, act as a highly selective filter, act as a tool for active transport, control the entry of nutrients and the exit of metabolic products, maintain cell differentiation.  Plasma Membrane Properties The main property of cell membranes is that they are very dynamic. Structure of plasma membrane determine thr dynamic membrane property. For example, the properties of a membrane that depend on its structure are the presence of two layers of fat that make up the membrane (lipid bilayer). Lipid membranes can form spontaneously from a mixture of lipids in an aqueous environment when the lipid concentration exceeds a certain critical value. If the amount of lipid is less than this critical concentration, the lipid is soluble in water.  Plasma membrane lipids Again Fifty percent (50 %) of the components The plasma membrane is a lipid molecule that is insoluble in water, and very easily soluble in organic solvents, while the rest of the component is mostly protein. Lipid molecules are arranged regularly as two layers of fat (lipid bilayer) 5 nm thick.  Lipid Bilayer Fluidity and Thinness The more unsaturated fatty acid content causes the lipid layer to become thinner. Plasma membranes can experience physicochemical changes (phase transition), namely from a watery phase (liquid state) to a agar-like phase (gel state). The change of the aqueous to the gel phase is more difficult to occur if the membrane contains a lot of unsaturated fatty acids.  Plasma Membrane Proteins The physiological and pathological of the membrane are caused by the presence of proteins embedded in the lipi bilayer even thought the basic structure of the membrane is lipid molecules. The number and type of proteins contained in the plasma membrane vary from cell to cell.