Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download sugars
Document related concepts
Membrane potential wikipedia , lookup
Cell culture wikipedia , lookup
Signal transduction wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Cell-penetrating peptide wikipedia , lookup
Cell membrane wikipedia , lookup
Electrophysiology wikipedia , lookup
Transcript
Section Objectives • Explain how a cell’s plasma membrane functions. • Relate the function of the plasma membrane to the fluid mosaic model. All living cells must maintain a balance regardless of internal and external conditions. Survival depends on the cell’s ability to maintain the proper conditions within itself This process of maintaining the cell’s environment is called homeostasis Selective permeability is a process used to maintain homeostasis in which the plasma membrane allows some molecules into the cell while keeping others out. Cell (plasma) membrane Cells need an inside & an outside… separate cell from its environment cell membrane is the boundary IN food - sugars - proteins - fats salts O2 H 2O cell needs materials in & products or waste out OUT waste - ammonia - salts - CO2 - H2 O products - proteins Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery FATS environment? LIPIDS What substance do you know that doesn’t mix with water? Remember: oil & water don’t mix!! Lipids of cell membrane Membrane is made of special kind of lipid phospholipids “split personality” “attracted to water” Membrane is a double layer phospholipid bilayer phosphate inside cell lipid outside cell “repelled by water” Makeup of the phospholipid bilayer The fluid mosaic model describes the plasma membrane as a flexible boundary of a cell. The phospholipids move within the membrane. Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? sugar lipids aa O2 H 2O salt waste Crossing the cell membrane What molecules can get through the cell membrane directly? fats and oils can pass directly through lipid inside cell salt waste outside cell sugar aa H 2O but… what about other stuff? Cell membrane channels Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell waste H 2O salt aa sugar outside cell How do you build a semipermeable cell membrane? Channels are made of proteins proteins both “like” water & “like” lipids bi-lipid membrane protein channels in bi-lipid membrane Movement through the channel Why do molecules move through membrane if you give them a channel? HIG H? LOW ? Molecules move from high to low Diffusion move from HIGH to LOW concentration Diffusion Move from HIGH to LOW concentration passive transport no energy needed diffusion diffusion of water osmosis Simple Diffusion Move from HIGH to LOW fat inside cell LOW fat fat fat fat fat HIG H outside cell fat fat fat fat fat fat Which way will fat move? fat fat Facilitated Diffusion Move from HIGH to LOW through a channel sugar inside cell LOW sugar sugar sugar sugar sugar Which way will sugar move? HIG H outside cell sugar sugar sugar sugar sugar sugar sugar Diffusion Move from HIGH to LOW concentration directly through membrane simple diffusion no energy needed help through a protein channel facilitated diffusion HIGH (with help) no energy needed LOW Simple vs. facilitated diffusion simple diffusion inside cell lipid facilitated diffusion inside cell H2O protein channel outside cell outside cell H2O Osmosis: Diffusion of Water The diffusion of water across a selectively permeable membrane is called osmosis. Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell. Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. Osmosis Water is very important, so we talk about water separately Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane What controls osmosis? Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis. Before Osmosis Selectively permeable membrane After Osmosis Water molecule Sugar molecule Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater Cells in an isotonic solution isotonic solution(= concentrations) the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. H2O H2O Water Molecule Dissolved Molecule Cells in an isotonic solution H2O H2O Water Molecule Dissolved Molecule water molecules move into and out of the cell at the same rate, and cells retain their normal shape. Cells in an isotonic solution A plant cell has its normal shape and pressure in an isotonic solution. Keeping right amount of water in cell Balanced conditions (isotonic) That’s balanced better! no difference in concentration of water between cell & environment cell in equilibrium example: blood I could problem: none be better… water flows across membrane equally, in both directions volume of cell doesn’t change Cells in a hypotonic solution hypotonic solution: dilute solution thus low solute concentration In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2O H2O Water Molecule Dissolved Molecule Cells in a hypotonic solution Plant cells swell beyond their normal size as pressure increases. (plants prefer this –it makes the leaves firm) Keeping right amount of water in cell Freshwater -Hypotonic freshwater KABOOM! a cell in fresh water high concentration of water around cell cell gains water example: Paramecium problem: cells gain water, swell & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell No problem, here Controlling water Contractile vacuole in Paramecium Cells in a hypertonic solution hypertonic solution: concentrated solution, thus a high solute concentration In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink H2O H2O Water Molecule Dissolved Molecule Cells in a hypertonic solution Plant cells lose pressure as the plasma membrane shrinks away from the cell wall. PLASMOLYSIS Keeping right amount of water in cell Saltwater -Hypertonic saltwater I’m shrinking, I’m shrinking! a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water in plants: plasmolysis in animals: shrinking cell solution: take up water I will survive! Passive Transport When a cell uses no energy to move particles across a membrane passive transport occurs Particles go DOWN their concentration gradient. all diffusion & osmosis are passive transport. Plasma membrane Concentration gradient Active Transport active transport :Movement of materials through a membrane against a concentration gradient and requires energy from the cell. Cellular energy Plasma membrane Carrier proteins Concentration gradient Cellular energy Active transport Cells may need molecules to move against concentration “hill” need to pump “uphill” from LOW to HIGH using energy protein pump requires energy ATP ATP How active transport occurs a transport protein called a carrier protein first binds with a particle of the substance to be transported. Each type of carrier protein has a shape that fits a specific molecule or ion. Transport of Large Particles Endocytosis is a process by which a cell surrounds and takes in material from its environment. The material is engulfed and enclosed by a portion of the cell’s plasma membrane. resulting vacuole with its contents moves to the inside of the cell Exocytosis is the expulsion or secretion of materials from a cell. Endocytosis Exocytosis Osmosis Osmosis Osmosis is the diffusion of water. Water moves from a high concentration to an area of low concentration. During equilibrium, there is an equal amount of water on the inside and outside of the cell. Cells in a Saline (Salt) Solution When the concentration of water decreases outside of the cell, water will diffuse out of the cell. High concentration to a low concentration. Place a cell in distilled water (100%) What do you believe will happen to a cell that is placed in distilled water? Osmosis Why should you never drink salt water if you stranded at sea? When you receive a IV at a hospital, why should they not give you distilled water? Why do movie theaters add salted butter to popcorn at the movie theater?
