Hello everyone. Welcome to my YouTube channel biotech and science. Today we will discuss about the plasma membrane. The plasma membrane. The plasma membrane, also known as the cell membrane, is a crucial structure that surrounds the cell's cytoplasm, separating it from the external environment. Here are some key points about the plasma membrane. Composition. It primarily consists of a phospholipid bilayer, with proteins interspersed within or attached to it. The phospholipid bilayer forms a barrier that is selectively permeable, allowing certain substances to enter or leave the cell while restricting others. Function. The main function of the plasma membrane is to regulate the passage of substances in and out of the cell. It controls the movement of ions, nutrients, waste products, and other molecules to maintain cellular homeostasis. Protein functions. Proteins embedded within the membrane serve various roles, including transport of substances across the membrane, cell signaling, cell recognition, and providing structural support. Fluid mosaic model. The arrangement of molecules in the plasma membrane is described by the fluid mosaic model, depicting a dynamic structure where proteins and lipids are not fixed, but rather move and interact within the membrane. Selective permeability. The plasma membrane is selectively permeable, meaning it allows specific molecules to pass through via processes such as diffusion, osmosis, facilitated diffusion, and active transport. Cell communication. Cell cell recognition and communication are facilitated by proteins on the membrane's surface, which allow cells to recognize each other, interact, and transmit signals. The plasma membrane structure and function are crucial for maintaining the integrity of the cell and allowing it to interact with its environment, enabling essential processes for cell survival and function. Lipid bilayer composition. The phospholipids in the membrane are amphipathic. Having a hydrophilic means water-tracting, head and hydrophobic means water-repelling, tails. This arrangement results in the bilayer structure with the hydrophobic tails facing inward and the hydrophilic heads facing outward towards the aqueous environments inside and outside the cell. Collestoral. Collestoral molecules are interspersed within the lipid bilayer. They help stabilize the membrane's fluidity, preventing it from becoming too rigid or too fluid by interacting with the phospholipids. Membrane proteins. There are two types of membrane proteins, integral proteins, which are embedded within the lipid bilayer and peripheral proteins, which are attached to the surface. Integral proteins can serve as channels or transporters for specific substances. While peripheral proteins often function in cell signaling, anchoring the membrane, or maintaining cell shape. Glycoproteins and glycolipids. Carbohydrate chains attached to proteins, glycoproteins, or lipids, glycolipids. Are present on the exterior surface of the plasma membrane. These molecules are involved in cell recognition, cell-to-cell communication, and the immune response. Membrane fluidity. The membrane is dynamic, allowing movement of lipids and proteins within it. This fluidity is essential for various cellular processes and the flexibility of the membrane. Membrane transport. The plasma membrane employs various mechanisms for transport. Passive transport. Includes diffusion, which is movement of molecules from high to low concentration, and facilitated diffusion, which is the aided movement through protein channels or carriers without energy input. Active transport. Requires energy, usually ATP, to move substances against their concentration gradient, often facilitated by specific protein pumps or carriers. Endocytosis and exocytosis. These processes involve the membrane forming vesicles to transport large molecules or particles. Endocytosis. The cell engulfs substances by forming vesicles from the plasma membrane. Types include phagocytosis, engulfing solid particles, and pinocytosis engulfing liquids, exocytosis. Vesicles within the cell fuse with the plasma membrane, releasing their contents outside the cell. Membrane potential. Cells maintain an electrical potential across the membrane, known as the membrane potential. Generated by differences in ion concentrations between the interior and exterior of the cell. This potential is vital for nerve impulses, muscle contraction, and various cellular processes. Receptor proteins. These proteins on the plasma membrane surface bind to specific molecules, ligands, to initiate cellular responses or signal transduction pathways inside the cell. Membrane stability and repair. The plasma membrane can self-repair, minor damage through vesicle fusion, and lipid molecule rearrangement. Cells also have mechanisms to replace damaged membrane components to maintain membrane integrity.