Cell Membrane and Transport PDF

The Cell Membrane and Transport  Types of Transport Passive – Diffusion – Osmosis – Facilitated diffusion Active – Cell Membrane Pumps (use proteins) - Vesicle-mediated transport Endocytosis Exocytosis PASSIVE Diffusion Solute – substances...

The Cell Membrane and Transport  Types of Transport Passive – Diffusion – Osmosis – Facilitated diffusion Active – Cell Membrane Pumps (use proteins) - Vesicle-mediated transport Endocytosis Exocytosis PASSIVE Diffusion Solute – substances dissolved in fluid to form a solution (example: glucose, oxygen and carbon dioxide) Solvent – liquid in which solutes are dissoved PASSIVE Diffusion All particles are randomly moving – even in solid (referred to as the Brownian motion) Therefore, it is a natural phenomenon that over time, particles tend to spread themselves out evenly throughout any matter Definition: tendency of particles to move from an area of high concentration and more random collisions, to an area of low concentration and fewer collisions. PASSIVE Diffusion Equilibrium is established when the distribution of the particles is completely even When particles move from areas of high to low concentration they are moving down a concentration gradient Movement down the gradient is referred to as passive transport The driving force of the movement of many molecules through the cell membrane, like oxygen, carbon dioxide, alcohol, small lipids, is diffusion Factors that Affect Rate of Diffusion Molecule size Larger molecules have more difficulty diffusing across Molecule polarity Polar molecules have a more difficult time than non-polar molecules Molecule/ion Charged molecules/ions cannot charge diffuse across membrane Temperature Higher temperatures give molecules more energy to move across faster Pressure Higher pressure forces molecules across faster Diffusion in our Bodies - Gas Exchange in the Lungs Involves: air sacs in lungs, called alveoli, and specialized blood vessels called capillaries Alveoli and capillaries are extremely thin – short path for gases to travel from capillaries to alveoli Many capillaries surround a single alveolus – increasing the surface area for diffusion to occur quickly.  Higher oxygen gradient in freshly breathed in air of alveoli than in the de- oxygenated blood of capillaries…so the oxygen travels along this gradient from the alveolus into the bloodstream. Similarly, carbon dioxide moves along its concentration gradient… traveling from the blood into the alveolus air PASSIVE Osmosis A special case of diffusion. The movement of WATER molecules, across a selectively permeable membrane from an area of HIGH concentration to an area of LOW concentration until the water molecules on both sides of the membrane are equal, or until the pressures acting on either side of the membrane are equal to each other. Movement is NOT from mechanical stress. Depends on movement of the molecules. (Kinetic Molecular Theory) PASSIVE Osmosis Cell membranes are permeable to water because water molecules are small enough to sneak through Very important to life, especially to single- celled organisms. If too much water enters the cell, the cell may burst If too much water leaves the cell, the cell becomes FLACCID and may die.  Osmotic Concentrations Osmotic concentration is determined by the concentration of solutes in a solution HYPERTONIC When the fluid surrounding the cell is higher in dissolved ion concentration (or solute) than what is in a cell HYPOTONIC When the fluid surrounding the cell is lower in dissolved ion concentration (or solute) than what is in a cell ISOTONIC When the surrounding fluid of the cell has the same amount of dissolved ions (or solute) as the inside does  Isotonic Solution Equal water and solute concentration on both sides of the membrane. Same amount of water enters the cell as leaves the cell therefore there is no NET movement of material into or out of the cell Plant cells Animal cells  Hypotonic Solution Higher water concentration in the solution surrounding the cell than inside the cell membrane OR lower solute concentration in the solution than in the cell Water will enter the cell; cell expands. If a plant cell, the membrane is pushed If any animal cell takes on too much up against the cell wall. We say it is water the cell it bursts (lysis) TURGID (very firm).  Hypertonic Solution Higher solute concentration in the solution surrounding the cell than inside the cell membrane. water leaves the cell; cell shrinks and becomes FLACCID In plant cells, the cell membrane separates Animal cells will shrivel from the cell wall = PLASMOLYSIS (crenation) PASSIVE PASSIVE PASSIVE Facilitated Diffusion Molecules enter the cell through channels that exist in special transport channel proteins or carrier proteins that span the membrane Transport is still along the concentration gradient – so no cellular energy is required (no ATP)  3 Types of Transport Proteins for Passive & Active Transport  Channel Proteins Tubular shape (hollow cylinder) Exterior composed of amino acids with non-polar side chains (interact with non-polar fatty acid tails of phospholipids) Some remain open all the time, some are gated (open and close in response to signals like hormones, electrical charge, pressure, or light) Carry ions or small polar molecules  Carrier Proteins Have specific shapes to bind to specific molecules, transport them across membrane and release on other side Change shape while transporting Can carry larger molecules like glucose and amino acids  Active Transport Requires energy, either from ATP (Adenosine TriPhosphate) or an electrochemical gradient to move molecules or ions AGAINST a concentration gradient (from low to high concentrations) Requires Carrier Proteins e.g. Sodium/Potassium Pump  Primary Active Transport Carrier proteins that pump ions across a membrane AGAINST a concentration gradient Creates an electrochemical This movement of ions creates an electrical gradient gradient across the cell membrane because the outside of the membrane becomes positively charged and the inside becomes negatively charged.  Secondary Active Transport Uses an electrochemical gradient as a source of energy to transport molecules or ions across a cell membrane PRIMARY ACTIVE TRANSPORT SECONDARY ACTIVE TRANSPORT ACTIVE Membrane-Assisted Transport Used to transport molecules that are too big to go through a channel or carrier protein (i.e. macromolecules) Vesicles are formed to surround the molecule whether they are incoming or outgoing from the cell Exocytosis is the term applied when transport is out of the cell. Endocytosis is the term applied when transport is into the cell. ACTIVE Endocytosis Receptor- mediated Phagocytosis Pinocytosis endocytosis an entire particle, solid the external fluid receptor proteins on or cell is engulfed. or solute is the membrane binds to engulfed. the molecule to be engulfed. ACTIVE Exocytosis A process where a vesicle: – Moves to the cell membrane, fuses with cell membrane, releases its contents to the outside of the cell » Used when large protein molecules from the Golgi Complex need to be moved out of the cell  Exocytosis – examples: Insulin made in the pancreatic cells…via the process of exocytosis, insulin molecules leave the pancreas and travel in the bloodstream Digestive enzymes are made in the specialized cells of the lining of the intestines…via the process of exocytosis, these enzymes are able to leave the lining and enter the interior of the intestine … where digestion occurs.