Cell Biology: Understanding Cellular Organelles, Membranes, and Osmosis, Lecture notes of Neurology

Download Cell Biology: Understanding Cellular Organelles, Membranes, and Osmosis and more Lecture notes Neurology in PDF only on Docsity! 9/14/2022 1 Lecture 2: Review 9/22/22 Sources: Quantitative Physiology for Engineers (Feher) Medical Physiology (Boron and Boulpaep) Human Physiology (Widmaier, Raff and Strang) Human Physiology (Silverthorn) Topics • Cell Organelles • Cellular Membrane • Diffusion • Osmosis • Tonicity Cells: Building Blocks of Biological Organisms Trillions of cells in the human body Cellular Organelles Lysosomes: digestive enzymes that break down various biomolecules Golgi Complex: processing and packaging proteins into vesicles Mitochondrion: energy (ATP) production Endoplasmic Reticulum (ER): protein and lipid synthesis and Ca+ storage Ribosomes: protein synthesis/creation from amino acids Nucleus: storage of genetic information Cytoskeleton: internal scaffolding/ skeleton of the cell used for transport Cytosol: fluid inside the cell Extracellular Fluid: fluid that surrounds the cells Functions of the Cellular Membrane All cells are surrounded by a cellular membrane that serves several important functions: • Separates two aqueous compartments (cytoplasm inside the cell and the extracellular fluid outside the cell) • Selectively permeable – some molecules able to pass through into or out of the cell, but others are unable to cross • Impermeable to charged molecules – separation of ions • Potential difference across the membrane – act as capacitors • Encapsulates the organs of the cell The Cellular Membrane is Composed of Phospholipids • Phospholipids are amphipathic – molecules that have polar and nonpolar regions • Phospholipids cluster in water with the polar/hydrophilic end at the surface and nonpolar region (tail) towards the interior 9/14/2022 2 Proteins are Embedded in the Cellular Membrane • Trans-membrane proteins serve as channels for charged ions and receptors for cellular communication. • Proteins that leave the cell act as signals to other cells and provide materials for forming the extracellular matrix. • Proteins are large and usually charged molecules. • Both make them difficult to diffuse through the cell membrane. Selective Permeability of the Cellular Membrane Size and charge affect the rate of diffusion across a membrane Selective Permeability of the Cellular Membrane Transport across the membrane occurs through different mechanisms: 1. Diffusion/Facilitated Diffusion 2. Carrier-mediated Transport 3. Ion channels Osmosis The movement of solvent (e.g. water) across a semipermeable membrane in response to a solute concentration gradient • Usually there is an imbalance of total ion (solute) concentrations between the two sides of the membrane. • Water is usually permeable through the membrane and will move from a region of lower to higher solute concentration, in order to equalize the solute concentrations on the two sides. • As water moves from one side to another, there will be a change in the volume. Tonicity - Describes a solution and how that solution affects cell volume Isotonic solution: osmotic balance, solute concentration is the same as the intercellular solution. No net movement of water Hypotonic solution: osmotic imbalance, solute concentration is lower than the intercellular solution. Water moves into the cell Hypertonic solution: osmotic imbalance, solute concentration is higher than the intercellular solution. Water moves out of the cell http://withfriendship.com/user/mithunss/tonicity.php Osmotic Pressure Osmotic pressure arises from unequal solute concentrations across a semipermeable membrane. This pressure is proportional to solute concentration and describes by van’t Hoff’s Law: The osmotic pressure difference ( ∆𝜋 ) depends on the net imbalance of solute concentrations across the membrane (∆𝐶). The larger the concentration difference between two solutions, the larger the osmotic pressure difference driving water transport. 𝜋 = 𝑅𝑇 𝐶 𝐶 Concentration of the solute 𝑅 Universal gas constant 𝜋 Osmotic pressure 𝑇 Absolute temperature (Kelvins) ∆𝜋 = 𝑅𝑇 ∆𝐶