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Transcript
7-3 Cell Boundaries Annette Lualhati Objectives 1. Identify the main functions of the cell membrane and the cell wall. 2. Describe what happens during diffusion. 3. Explain the process of osmosis, facilitated diffusion, and active transport. Vocabulary Cell membrane hypertonic Cell wall hypotonic Lipid bilayer facilitated diffusion Concentration active transport Diffusion endocytosis Equilibrium phagocytosis Osmosis pinocytosis Isotonic exocytosis Review Cell Membrane – flexible barrier of cell that regulates what enters and leaves the cell. The cell membrane is “semipermeable”. The lipid bilayer and the structure and composition of a glycerophospholipid molecule Figure 1: (A) The plasma membrane of a cell is a bilayer of glycerophospholipid molecules. (B) A single glycerophospholipid molecule is composed of two major regions: a hydrophilic head (green) and hydrophobic tails (purple). (C) The subregions of a glycerophospholipid molecule; phosphatidylcholine is shown as an example. The hydrophilic head is composed of a choline structure (blue) and a phosphate (orange). This head is connected to a glycerol (green) with two hydrophobic tails (purple) called fatty acids. (D) This view shows the specific atoms within the various subregions of the phosphatidylcholine molecule. Note that a double bond between two of the carbon atoms in one of the hydrocarbon (fatty acid) tails causes a slight kink on this molecule, so it appears bent. The Cell Membrane The fluid-mosaic model describes the plasma membrane of animal cells. The plasma membrane that surrounds these cells has two layers (a bilayer) of phospholipids (fats with phosphorous attached), which at body temperature are like vegetable oil (fluid). And the structure of the plasma membrane supports the old saying, “Oil and water don’t mix.”. Each phospholipid molecule has a head that is attracted to water (hydrophilic: hydro = water; philic = loving) and a tail that repels water (hydrophobic: hydro = water; phobic = fearing). Both layers of the plasma membrane have the hydrophilic heads pointing toward the outside; the hydrophobic tails form the inside of the bilayer. Because cells reside in a watery solution (extracellular fluid), and they contain a watery solution inside of them (cytoplasm), the plasma membrane forms a circle around each cell so that the water-loving heads are in contact with the fluid, and the waterfearing tails are protected on the inside. Proteins and substances such as cholesterol become embedded in the bilayer, giving the membrane the look of a mosaic. Because the plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances are able to move across it. The molecules that are embedded in the plasma membrane also serve a purpose. For example, the cholesterol that is stuck in there makes the membrane more stable and prevents it from solidifying when your body temperature is low. (It keeps you from literally freezing when you’re “freezing.”) Carbohydrate chains attach to the outer surface of the plasma membrane on each cell. These carbohydrates are specific to every person, and they supply characteristics such as your blood type. Cell Membrane & Cell Wall Cell Wall – protects cell and give cell structure. Found only in plant cells. Made mostly of cellulose. Introduction Student Activity Diffusion In a solution, particles move constantly. Diffusion – tendency of particles to move from an area of high concentration to an area of low concentration. Diffusion Through Cell Boundaries Every living cell exist in a liquid environment that it needs to survive. The cytoplasm of a cell contains a solution of many different substances in water. Concentration of a solution = mass of solute/volume of solution. Diffusion When do the particles of solute stop moving? When the concentration of solute is the same throughout, and the system has reached equilibrium (homeostasis). Osmosis Water diffuses across membranes more easily than other substances. Osmosis – diffusion of water across semi-permeable membrane. How Osmosis Works http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/ani mation__how_osmosis_works.html Tonicity of a Solution Isotonic – The concentration of solutes is the same inside and outside of the cell. Hypotonic – Solution has a lower solute concentration than the cell. Hypertonic – Solution has a higher solute concentration than the cell. For organisms to survive their cells must balance the intake of water, salts, sugars, and other molecules. What if a cell is placed into a isotonic solution? What if a cell is placed into a hypertonic solution? What if a cell is placed into a hypotonic solution? The Effect of Osmosis on Cells Osmotic Pressure Hypertonic Isotonic Hypotonic Facilitated Diffusion: So why don’t our cells burst open shrivel up? http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/ani mation__how_facilitated_diffusion_works.html Facilitated Diffusion A concentration gradient is when there is an uneven distribution of a substance across a border. For example, think of a balloon. The air inside the balloon is more concentrated than the air outside of it. There is a concentration gradient because of the differences in concentration. And what happens when you release the tip of the balloon? The air inside the balloon shoots out because things like it when the concentration is equal everywhere. So when something moves against its concentration gradient, it is being forced from an area where it is less concentrated into a place where it is more concentrated. Conversely, when something moves down its concentration gradient, it is going from a place where it is more concentrated to where it is less concentrated. However, it is important to note that ENERGY MUST BE EXPENDED TO MOVE SOMETHING AGAINST ITS CONCENTRATION GRADIENT, but no energy must be used to move something down its concentration gradient. Facilitated Diffusion Some molecules seem to pass through the cell membrane more easily than they should. Example: RBC’s have a glucose (sugar) channel that allows glucose to pass in and out. Only glucose can pass through the channel. Facilitated Diffusion . Facilitated Diffusion – is the diffusion of particles through protein channels, Hundreds of channels have been found to allow only one specific material through. Carbohydrates and sugars mostly Hyper link Active Transport Active transport – transport of materials that requires energy. Uses “pumps” that are found in the membrane. The most common pump is the sodium (Na) – potassium (K) (salts) Active Transport Uses energy to move molecules from low to high concentration (against concentration gradient). http://highered.mcgrawhill.com/sites/00724958 55/student_view0/chapt er2/animation__how_the _sodium_potassium_pu mp_works.html Active Transport + 1 Cytoplasmic Na binds to the sodium-potassium pump. EXTRACELLULAR+ [Na ] high FLUID [K+] low Na+ Na+ [Na+] low Na+ CYTOPLASM [K+] high + + 3 K is released and Na sites are receptive again; The cycle repeats. 2 Na+ binding stimulates phosphorylation by ATP. Na+ Na+ Na+ P ADP ATP 4 Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside. Na+ Na+ Na+ K+ P K+ 5 Loss of the phosphate restores the protein’s original conformation. + 6 Extracellular K binds to the protein, triggering release of the Phosphate group. K+ K+ K+ K+ P Pi To Relieve Confusion… Passive Transport 1)Diffusion 2)Osmosis 3)Facilitated Diffusion NO ENERGY REQUIRED!!! Active Transport 1)Active Transport REQUIRES ENERGY!!! Passive transport Active transport Endocytosis and Exocytosis Endocytosis is a process for moving items that are outside of the cell into the cytoplasm of the cell. Exocytosis is a process for moving items from the cytoplasm of the cell to the outside. http://www.youtube.com/watch?v=4gLtk8Yc1Zc Phagocytosis The process of engulfing and ingestion of particles by the cell or a phagocyte (e.g. macrophage) to form a phagosome (or food vacuole), which in turn fuse with lysosome and become phagolysosome where the engulfed material is eventually digested or degraded and either released extracellularly via exocytosis, or released intracellularly to undergo further processing. http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/ani mation__phagocytosis.html