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Transcript
Homeostasis means maintaining a balance internally despite what is going on externally. Organisms must adjust to changes in the environment in order to survive or they could die! For example, if it is below freezing outside, you must put on a heavy coat, gloves, double socks, a warm hat, ear muffs, and lots and lots of layers to maintain a healthy INTERNAL body temperature despite the EXTERNAL temperature What structure maintains homeostasis in our cells? The Cell Membrane How does it maintain homeostasis? By controlling the passage of molecules, such as water, salts, food particles, etc in and out of the cell. (it regulates what enters and leaves) How? Through passive transport, active transport and cell to cell communication! The Cell Membrane is: A phospholipid bilayer Two layers made of proteins and lipids Phospholipid Structure: Polar Head (hydrophilic—”water loving”) Nonpolar Tails—(hydrophobic—”water fearing”) Draw: Polar Head (hydrophillic) Nonpolar Tails (hydrophobic) Bilayer arrangement Draw: The proteins embedded in the cell membrane help it to function properly 3 Types of Membrane Proteins › › › Transport — helps molecules enter or leave the cell Marker — identify the cell Receptor — allow cells to communicate Transport Proteins Function as “gates/passageway” Transport Protein Allow sugars, salts, etc to cross the membrane. Special channel proteins: › Gated ion channels— gates that open/close › Carrier proteins—change shape to allow specific molecule to pass › Aquaporins - allow water to diffuse through (called osmosis) Carrier Protein Channel Protein Marker Proteins Cell’s “Name Tag” Protein sticks out of phospholipid layer Often has carbohydrates attached to outside end Functions in cell identification to identify the cell to other cells and molecules Marker Protein Important in › immunity—so various white blood cells in your body do not mistake your cells for foreign cells - blood typing – so you can’t receive just any ol’ type of blood Receptor Proteins Function as “messenger/receiver” Receive information from the environment (extracellular fluid, blood, interstitial fluid) and transmit that info to the inside of the cell Protein has specific shape/charge to only allow certain molecules (like hormones) to bond Triggers a response in cell http://personal.tmlp.com/Jimr57/ textbook/chapter3/cms2.htm Receptor Protein Remember that these proteins are embedded or floating in the lipid bilayer. The Cell Membrane is: Selectively permeable/semipermeable permeable means to let objects travel through so if it is selectively or semi permeable it only allows SOME things through and not others This represents a selectively permeable membrane. It allows (selects) certain things to pass through it. Is the membrane permeable to Is the membrane permeable to ? ? Molecules pass through the cell membrane through: › Passive Transport Diffusion Facilitated Diffusion Osmosis › Active Transport Vesicles Pumps Molecule- the smallest unit of a compound/substance › Cannot be seen with the naked eye › 1 drop of water has 16,700,000,000,000,000,000,000 molecules of H20 › 1 grain of salt has 120,000,000,000,000,000 molecules of salt Concentration Gradientan area of high concentration next to an area of low concentration High Concentration of Molecules Low Concentration of Molecules Equilibrium is when there is an EQUAL amount of molecules on each side of the membrane There is no net movement meaning, there is continuous movement of molecules back and forth through the membrane. Passive Transport is when molecules move from an area of HIGH concentration to an area of LOW concentration until equilibrium is reached. Requires NO ENERGY! Examples: › Diffusion › Osmosis › Facilitated Diffusion Diffusion - the process by which molecules (“stuff”) spread from areas of high concentration, to areas of low concentration Molecules are said to go “Down” or “with” the concentration gradient. Requires no energy What will Where is the happen greatest least when concentration concentration the gate is of cows? opened? This process is called… diffusion Facilitated Diffusion › What does facilitate mean? › When substances move from high to low concentration (down the concentration gradient) using channel/carrier proteins located in membrane › Does not require energy http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation.html Click, hold, and drag slider to move forward, bckword, or slow down A special type of diffusion is called osmosis Osmosis- the process by which WATER molecules move from an area with a high concentration of water to an area of low concentration of water. › OR the “diffusion of water” Requires no energy In Osmosis water will move in where there is a low concentration of SOLVENT, and a high concentration of SOLUTE ›A solute = “stuff” (salt, glucose, food particles) ›A solvent = “water” There are three ways water can move in a solution: › Hypotonic- water moves INTO a cell and the cell swells (gets bigger) › Hypertonic – water moves OUT of a cell and the cell shrinks (gets smaller) › Isotonic- water moves into AND out of a cell at an equal rate (remember- molecules are constantly moving) Hypotonic -Describes a solution that is LESS CONCENTRATED (has less solute, more water) o When a cell is placed in a hypotonic solution, the cell will swell as water moves INTO the cell. Hypotonic (continued) there is more solvent/less solute on the outside of the cell that the inside The solvent (water) moves to an area of low solvent (water) concentration The cell could burst (lyse) Hypertonic-- describes a solution that is MORE CONCENTRATED (has more solute, less water) o When a cell is placed in a hypertonic solution, water moves out of a cell and the cell shrinks (gets smaller) Hypertonic (continued) There is less solvent/more solute on the outside on the cell than the inside The solvent (water) moves to an area of low solvent (water) outside Isotonic – describes a solution that is of EQUAL concentration to another water moves into and out of the cell at an equal rate(remember – molecules are constantly moving) No change in the size of the cell will be observed The concentration of solvent and solute on the inside of the cell is equal to the concentration of solvent and solute on the outside of the cell Draw arrows to show the flow of water Label at the top if the solution is isotonic, hypotonic or hypertonic Where is the greatest concentration of solvent? Outside of the bag Which way does the water move? Into the Bag What type of solution is this? Hypotonic selectively permeable membrane Where is the greatest concentration of solvent? In the bag Which way does the water move? Out of the bag 90% water 10% salt What type of solution is this? Hypertonic selectively permeable membrane What happens to the bag? 90 % solvent 10% salt selectively permeable membrane What happens to the bag? 90 % solvent 10% salt selectively permeable membrane What happens to the bag? 90 % solvent 10% salt selectively permeable membrane What happens to the bag? The bag shrinks. 90 % solvent 10% salt selectively permeable membrane Passive transport Recap: › requires no energy › moves from high concentrations to low concentrations › Moves down the concentration gradient › Includes diffusion, facilitated diffusion and osmosis When molecules are forced from a low concentration to a high concentration they must use active transport Cells must transport certain amino acids, sugars, etc. into their cytoplasm from the surrounding fluid. Some of these substances, however, are already in higher concentrations inside versus outside. This requires energy! Opposite of Passive Transport Forces molecules to go against the concentration gradient Energy is provided by the ATP made in the mitochondria Pumps allow molecules to travel against their concentration gradient 1. Sodium/Potassium Pump For example, the sodium/potassium pump actively transports sodium molecules and potassium molecules through the cell membrane Requires energy Na+ pumped out of a cell K+ pumped into a cell Important because it prevents cells from bursting by lowering the sodium inside causing less water to enter through osmosis. Sodium Potassium Pump Proton (H+) pump – forces protons out of a membrane enclosed space (organelle or cell), often to create a proton gradient down which the protons can flow back in Why would the cell “waste” energy on a proton pump? *Because the cell needs isolated areas of the cell with different pH for particular functions; ex) lysosomes – have proton pumps to maintain a pH=5 *Because the cell only uses one ATP to pump a proton out, and that proton can be used in cotransport Co-transport – process cells use to bring large molecules, such as sugars, into a cell with a minimum amount of energy used; usually a proton and a sugar enter a double tunneled protein at the same time; the tunnel only “works” when both molecules are present Vesicles can transport molecules across the cell membrane through: › Endocytosis- moving INTO the cell Pinocytosis – moving a liquid into a cell Phagocytosis – moving a solid into a cell Pinocytosis (drinking) Phagocytosis (eating) › Exocytosis- moving OUT of the cell Excretion – moving waste out of the cell after something is digested by a lysosome Secretion – moving a cell product (like glucose or insulin) out of a cell Opposite of Passive Transport Molecules go against the concentration gradient (from low to high concentration) Energy is provided by the ATP made in the mitochondria Active transport can involve pumps or vesicles Requires energy