Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Endocytosis is an energy-dependent cellular process in which the plasma membrane undergoes invagination and budding to internalize extracellular material, membrane proteins, lipids, fluids, or macromolecules into intracellular vesicles. It is a fundamental mechanism of: Basic concept 2. Why Is Endocytosis Important? The plasma membrane is not static. Cells continuously: Therefore: Endocytosis is both a transport mechanism and a major regulator of cellular signaling and membrane homeostasis. 3. Major Types of Endocytosis Endocytosis can broadly be classified into: 1. Phagocytosis Uptake of large particles. 2. Pinocytosis Uptake of extracellular fluid and dissolved molecules. 3. Receptor-mediated endocytosisRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Ca²⁺ pumps are ATP-dependent membrane transport proteins that actively move Ca²⁺ against its electrochemical gradient. They are essential for maintaining the very low free cytosolic Ca²⁺ concentration required for cellular signaling. The major Ca²⁺ pumps are: Both belong to the P-type ATPase family. 2. Why Ca²⁺ Must Be Tightly Controlled Ca²⁺ is not simply an electrolyte. It is a major second messenger. Changes in cytosolic Ca²⁺ regulate: Therefore, cells maintain a very steep Ca²⁺ gradient. Conceptual distribution The cytosolic free Ca²⁺ concentration is typically maintained around the 10⁻⁷ M range, whereas extracellular Ca²⁺ is roughlyRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition ABC transporters (ATP-Binding Cassette transporters) are a large superfamily of membrane proteins that use the energy derived from ATP hydrolysis to transport a wide variety of substrates across biological membranes. They are found in: ABC transporters can transport: Key principle: ABC transporters are primary active transporters because ATP hydrolysis directly provides the energy required for transport. 2. Meaning of ABC ABC = ATP-Binding Cassette The name refers to a conserved intracellular ATP-binding domain known as the ABC cassette. The cassette contains characteristic nucleotide-binding motifs, particularly: 3. Basic Architecture A typical complete ABC transporter contains twoRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Ion channels are integral membrane proteins that form selective, aqueous pathways across the lipid bilayer through which ions move down their electrochemical gradients. They are fundamental to: Key principle: Ion channels provide a pathway for ion movement but generally do not actively pump ions against their electrochemical gradients. 2. Basic Structure of an Ion Channel An ion channel generally contains: A simplified arrangement: The pore is lined by amino-acid residues that determine ion selectivity and influence ion permeation. 3. Ion Channels vs Transporters Ion channels and carrier proteins should not be confused. Feature Ion channelRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Introduction Diffusion is the net movement of molecules from a region of higher chemical potential or concentration toward a region of lower chemical potential as a consequence of random molecular motion. In biological membranes, diffusion is an important mechanism for movement of: Two major forms are: Both are passive transport mechanisms, meaning they do not directly require metabolic ATP hydrolysis. 2. The Fundamental Principle The direction of passive transport is determined by the relevant electrochemical gradient. For an uncharged solute: [\Delta \mu = RT\ln\left(\frac{C_2}{C_1}\right)] where: For ions, electrical potential must also be considered. Thus: Ion movementRead More →