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Transcript
Chapter 7 Membrane Structure/ Function and Cell Transport Ms. Gaynor AP Biology Overview of Cell Membrane The plasma (cell) membrane the boundary that separates living cell from its nonliving surroundings Also called the phospholipid bilayer The plasma membrane exhibits selective permeability. It is semi-permeable It allows some substances to cross it more easily than others Wow… it’s so detailed! Cellular membranes are made of 2 types of lipids and proteins LIPID #1: Phospholipids most abundant lipid in membrane They are amphipathic have both hydrophobic and hydrophilic regions Phospholipid Bilayer Phosphate Groups in “head” (- charge) 2 Fatty Acids in “tail” (hydrocarbon) Hydrophilic head Hydrophobic tail Figure 7.2 WATER NO WATER WATER In 1972, scientists Proposed that membrane proteins are mixed in and individually inserted into the phospholipid bilayer Hey, that looks like a sandwich! Hydrophobic region of protein Phospholipid bilayer Hydrophobic region of protein Polar heads love water & dissolve. Fluid Mosaic Model of the cell membrane Non-polar tails “hide” from water. Carbohydrate cell markers Proteins Membrane movement animation The Fluidity of Membranes Phospholipids in the plasma membrane Can move within the bilayer Proteins are larger & drift (move) less Lateral movement (~107 times per second) (a) Movement of phospholipids Figure 7.5 A Flip-flop (~ once per month) Another view… Temperature decreases so does fluidity Hydrocarbon tails in phospholipids Affects fluidity of the plasma membrane Need to have some unsaturated fatty acid tails Fluidity is enhanced Fluid Unsaturated hydrocarbon tails with kinks (b) Membrane fluidity Figure 7.5 B Viscous Saturated hydroCarbon tails LIPID #2: steroid “cholesterol” has different effects on membrane fluidity at different temperatures (only in animal cells) -lower temps lowers lipid movement lowers fluidity - cholesterol in membrane hinders (stops) solidification **acts as a temp “buffer” Cholesterol (c) Cholesterol within the animal cell membrane Membrane Proteins and Their Functions A membrane Includes different proteins embedded in the fluid lipid bilayer Fibers of extracellular matrix (ECM) 2 major types of membrane proteins Glycoprotein Carbohydrate GlycolipidEXTRACELLULAR SIDE OF MEMBRANE Microfilaments of cytoskeleton Cholesterol Peripheral protein Integral CYTOPLASMIC SIDE protein OF MEMBRANE 1. Integral proteins Penetrate the hydrophobic core of the lipid bilayer Are often transmembrane Wait…what’s that proteins, completely word for a polar & spanning the membrane nonpolar molecule? Span of 1+ stretches of Nonpolar amino acids Figure 7.8 EXTRACELLULAR SIDE a Helix CYTOPLASMIC SIDE 2. Peripheral proteins Are appendages loosely bound to the surface of the membrane An overview of six major functions of membrane proteins (a) (b) (c) Transport. Enzymatic activity. Signal transduction. Enzymes Signal Receptor (d) (e) (f) Cell-cell recognition. Intercellular joining Attachment to cytoskeleton & extracellular matrix (ECM) Glycoprotein ECM Why have Carbohydrates on Cell Membrane proteins? Cell-cell recognition Is a cell’s ability to distinguish one type of neighboring cell from another It’s their “ID” tag Membrane carbohydrates Usually short, branched carbohydrates Interact (bind) with the surface molecules of other cells Function as cell “markers” • Ex: Blood types (A, B, AB, and O) 2 different types membrane carbohydrates Glycolipids Carbohydrates covalently attached to lipids Glycoproteins Carbohydrates covalently attached to proteins (most abundant) Review… Animations of membrane structure Chapter 7 Cell Transport Ms. Gaynor AP Biology Membrane structure LEADS TO selective permeability A cell must exchange materials with its surroundings a process controlled by the selectively permeable plasma membrane Cell Transport Means moving things INTO and OUT of the cell Cells need to take in Food, gases, water Get rid of waste products (excretion) Give out such useful substances as hormones and enzymes (secretion). Permeability and Cell Transport Hydrophobic (non polar) molecules Are lipid soluble (can dissolve) can pass through membrane easily Ex: Hydrocarbons, CO2, O2 Hydrophilic (Polar) molecules Are NOT lipid soluble (can’t dissolve) Lipid INsoluble Do not cross membrane easily Ex: Na+, Cl- , Glucose/ other sugars • NOTE: CHARGED molecules need “help” to cross membrane Types of Cellular Transport Weee! Passive Transport cell do NOT use energy 1. Diffusion 2. Facilitated Diffusion 3. Osmosis high low Active Transport cell DOESuse energy 1. Protein Pumps 2. Endocytosis 3. Exocytosis This is going to be hard! high low Types of Passive Transport Diffusion= tendency for a population of molecules (of ANY substance) to spread out evenly into available space A “net” movement Ex: Perfume, a fart , tea, food coloring in water http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html DIFFUSION In absence of other forces… Molecules move (diffuse) from area of HIGH [ ] to an area of lower [ ] A.k.a. Molecules move DOWN its OWN concentration gradient the difference in [ ] of a substance from one area to another No chemical work (ATP energy) is used diffusion is spontaneous! Substances diffuse down their OWN concentration gradient Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Equilibrium Factors Affecting Diffusion 1. Temperature Higher temperature more kinetic energy molecules move faster (Example: Tea) 2. Pressure Higher pressure molecules move faster Introduction to Osmosis https://www.youtube.com/watch?v=IaZ8Mt F3C6M Effects of Osmosis on Water Balance Osmosis The movement of water (water diffusion) across a semipermeable membrane Involves the movement of FREE water molecules down a water [ ] gradient High solute low “free” water [ ] Low solute high free water [ ] or…. Tonicity= the measure of the amount of dissolved particles in a solution https://www.youtube.com/watch?v=sdiJtDRJQEc Osmosis is affected by the concentration gradient of dissolved substances (solutes) Osmosis animation 3 Different Types of Solutions Recall: SOLUTION = a uniform mixture of 2 or more substances ** compare solutions OUTSIDE cell to inside cell 1. If a solution is isotonic [solutes] is the same outside as inside the cell “iso-” means “same” There will be NO net movement of water ISOTONIC SOLUTION Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium) 2. If a solution is hypertonic [solutes] is greater outside than inside the cell The cell will lose water and shrivel or wilt “hyper” means more (high [solute]) Ex: when salinity increases in lake, fish can die! HYPERTONIC SOLUTION Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)! 3. If a solution is hypotonic [solutes] is less outside than it is inside the cell The cell will gain water and swell (and maybe lyse or burst) “Hypo” is “hypo” means “less” LOW!!! • (low [solute]) Think: Hypo- sounds like hippo…hippos are big & round; cells in hypotonic solutions get big & round Also, think “hypo” is “low” meaning “low” solutes SURROUNDING cell HYP0TONIC SOLUTION Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)! Now…let’s review tonicity using Gummy Bears! https://www.youtube.com/watch?v=HqKlL m2MjkI • Osmosis Animations for isotonic, hypertonic, and hypotonic solutions http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html Water Balance of Cells with Walls Cell walls Help maintain water balance Cell walls are in: Plants Prokaryotes Fungi Some protists If a plant cell is turgid It is in a hypotonic environment It is very firm A healthy state in most plants If a plant cell is flaccid It is in an isotonic or hypertonic environment Cells are limp Plasmolysis= when plasma membrane pulls away from cell wall in hypertonic solutions ; causes cell with walls to wilt & can be lethal. Water balance in cells with walls H2O Turgid (normal) H2O H2O Flaccid H2O Plasmolyzed How Organisms Deal with Osmotic Pressure •Bacteria and plants have cell walls that prevent them from over-expanding. •In plants the pressure exerted on the cell wall is called tugor pressure. •A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from bursting. •Salt water fish pump salt out of their specialized gills so they do not dehydrate. •Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water. Types of Passive Transport #1 Passive Transport DOES NOT require chemical energy (ATP) Moves DOWN (WITH) [ ] gradient Kinetic energy drives movement #2 Active Transport DOES require chemical energy (ATP) Moves AGAINST its [ ] gradient 2 Types of PASSIVE TRANSPORT 1. SIMPLE DIFFUSION **INCLUDES DIFFUSION Uses NO membrane proteins GOES DOWN CONCENTRATION GRADIENT (no ATP needed) Molecules move HIGH [ ]low [ ] Uncharged & lipid-soluble molecules also pass freely through bilayer. solutes move down a concentration gradient • Examples: CO2, O2…H2O WAIT!!! Isn’t water polar? Aquaporins water is polar but very small It can pass easily through membrane uses aquaporins EXTRACELLULAR FLUID AQUAPORIN Channel protein Water CYTOPLASM Oh…now I get it! 2 Types of PASSIVE TRANSPORT 2. FACILITATED DIFFUSION needs a little “help” Uses help of channel or carrier proteins GOES DOWN CONCENTRATION GRADIENT (no ATP needed) Moves POLAR molecules can NOT easily pass through HYDROPHOBIC region of membrane. Example: ions, smaller polar molecules (ex: sugar) Channel/carrier proteins specific receptor site for substances they Channel proteins -Provide “tunnels” • Channel Proteins animations EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM (a) A channel protein (purple) has a channel through which water molecules or a specific solute can pass. Carrier proteins -Undergo a subtle change in shape “carry” solute across the membrane Carrier protein Solute 2 Types of Passive Transport Active transport Uses energy to move solutes against their [ ] gradients across the cell membrane Energy required usually ATP Carrier proteins are used…NEVER channel proteins Ex: sodium-potassium pump Passive vs. Active Transport Figure 7.17 1. PROTEIN PUMPS •Protein Pumps transport proteins that require energy to do work •Examples: •Na+/K+ Pumps are important in nerve responses •Antiports and Symports (Cotransport) •H+ (proton) pump Sodium Potassium Pumps (Active Transport using proteins) Protein changes conformational shape to move molecules: this requires energy! REVIEW OF ACTIVE TRANSPORT… ANIMATIONS •http://www.wisconline.com/objects/ViewObject.aspx?ID=a p11203 Cotransport, Proton Pumps and Sodium/Potassium Pumps… ANIMATIONS http://highered.mcgrawhill.com/sites/0072437316/student_view0/ chapter6/animations.html# 2. Bulk transport across the plasma membrane Occurs by exocytosis and endocytosis BOTH MOVE “BIG” AMOUNTS OF STUFF in OR out OF THE CELL Exocytosis In exocytosis Transport vesicles move to the plasma membrane, fuse with it, and release their contents “exo-” means “exit” Ex: hormone excretion; nerve cells and transmitters; removal of wastes ER 1 ROUGH ER Glycolipid 2 GOLGI APPARATUS Vesicle 3 4 Secreted protein Membrane glycolipid Endocytosis In endocytosis Cell takes in macromolecules by forming new vesicles from the plasma membrane “endo-” means “enter” 2 types of Endocytosis 1. Phagocytosis “cell eating” Cell engulfs SOLIDS into vesicle & “digests” it 2. Pinocytosis “pineapple juice) (think “cell drinking” Cell engulfs LIQUIDS into vesicle & “digests” it http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/ animation__phagocytosis.html Endocytosis and Exocytosis Animations http://highered.mcgrawhill.com/sites/0072437316/student_view0/ chapter6/animations.html# REVIEW ANIMATIONS http://www.hippocampus.org/Biology Click on “Membranes and Transport” Listen to animation #3 (7 minutes long) http://www.northland.cc.mn.us/biology/Biol ogy1111/animations/passive3.swf Excellent Review all Passive (simple/facilitated diffusion) and Active Transport No verbal explanation…you have to read the tutorial!