Plasma Membrane Function
Cells have to maintain homeostasis, they do this by controlling what moves across their membranes
Structure Double Layer of phospholipids Head (polar) hydrophiliclikes water - Charged phosphate group - Glycerol Tail (nonpolar) hydrophobic- hates water): - Two fatty acid chains
Water is polar What is cytoplasm mostly made of? Why do you think then that the phospholipids orientate themselves as in the diagram?
Cholesterol- strength Membrane proteinstransport Carbohydrates- ID Fluid Mosaic Model What does fluid mean? What is a mosaic? How is this related to the membrane?
Semipermeable Partially permeable Some not all materials cross Ex: waterproof clothing, how does it work? Cell maintains homeostasis Import and export of materials across the membrane Selective Permeability
Chemical Signals and the Cell Membrane Membrane secretes molecules and has ID molecules What is a Receptor? What is a ligand? Intracellular Receptor Molecule (small, nonpolar) crosses membrane and binds with a receptor inside the cell Ex: hormones Cells have to have specific kind of receptor
Membrane Receptor Molecules that can not cross the membrane will bind to a receptor in the membrane The receptor then triggers a series of chemical events that tell the cell what to do How are these two different?
Passive Transport Random movement of ions and other molecules across the membrane- No energy Vocabulary: Concentration Diffusion Net movement of molecules from a region of greater concentration to a region of lesser concentration = Concentration gradient: difference in concentration of molecules from one area to the next Particles become evenly disturbed over time = Dynamic equilibrium: continuous movement of molecules Particles can diffuse through air, water, other liquids and across membranes.
Diffusion through Membranes Particles that diffuse across membranes include lipids and those that can dissolve in lipids (molecules that are nonpolar) also small molecules Ex. Oxygen, from blood to respiring cells and carbon dioxide, during gas exchange between plants and atmosphere.
Osmosis Movement of water into and out of a cell through channels in a selectively permeable membrane. Also down a concentration gradient Cells need to achieve osmotic balance with their environment (the solution that surrounds them). When movement of water in and out is equal = dynamic equilibrium. Vocabulary: Solution, isotonic, hypertonic, hypotonic
EX: Osmotic Balance in Blood If Cell is in balance with surrounding blood plasma Q.What type of solution is this in relation to the red blood cell? Isotonic If blood cell is taken and placed in pure water, there is a net movement of water molecules into the cell, cell quickly swells and can burst. (IV given to patients are solutions of sugars and salts rather than pure water). Q.What type of solution is this in relation to the red blood cell? Hypotonic Q. What would happen to a cell placed in a hypertonic solution? Water would move out of the cell causing it to shrink
Osmotic Balance in Fresh Water Plants If the freshwater aquarium plant Elodea is placed in pure water net movement of water molecules is into the cell Q. Why does it not burst like the red blood cell? Does not burst like blood cell due to tough outer cell wall, balances outward pressure of water. Q. If the plant is placed in salt water (hypertonic) what will happen? water will move out of the cell and the vacuole would collapse
Diffusion and Osmosis as Passive Transport Review Osmosis and diffusion are examples of passive transport. Water, lipids and lipid soluble particles are able to either dissolve in the lipid bilayer or are small enough to squeeze between the PPL in the membrane. Passage due to their net random movement from a region of greater concentration to a region of lesser concentration. Cell does not work to move the particles. Called Passive as cell uses no energy.
Facilitated Diffusion Transport Proteins (channel and carrier) help the passage of molecules that do not dissolve in the lipid bilayer, are ions or are too large to squeeze through Ex, sugars (glucose) and amino acids Movement from a region of high concentration to a region of low concentration = No Energy Proteins are highly selective for one type of molecule based on shape and charge.
Active Transport Moves molecules against a concentration gradient from an area of low concentration to an area of high concentration Transport proteins function as pumps (membrane pumps) Change shape Requires the cell to use energy in the form of ATP Ex: Nerve cells: Sodium-potassium Pumptwo potassium ions are moved in and three sodium ions are moved out of the cell
Review
Vesicle Transport Vocabulary: Endocytosis, phagocytosis, exocytosis