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Transcript
Cell Boundaries I. Cell membranes essential for A. helping living organisms maintain homeostasis by controlling what substances may enter or leave cells (narrow range of pH and ionic concentration for metabolic activities to take place) B. Maintaining cell’s integrity – ensures a distinct identity (marker proteins embedded in phospholipid bilayer) II. Cell membrane structure A. Thickness – 7-9 nm (bilayer) B. Selectively permeable – next slide Small molecules like water, oxygen, & carbon dioxide can move in and out freely Large molecules like proteins & carbohydrates cannot move easily across the plasma membrane C. Chemicals found in membrane - Eukaryotic cell = phospholid, cholesterol, glycolipids, carbohydrate chains Prokaryotic cells = same except no cholesterol D. Fluid mosaic model 1. Structure is fluid – lipids and some proteins move laterally within the membrane Phospholipid Bilayer a. Hydrophobic tails – two fatty acids inward b. Hydrophilic heads (phosphates) outward c. Impermeable to ions and polar molecules (except water) d. Intergral proteins embedded – span the membrane and protrude on either side 3. Cytoplasmic side of membrane • Peripheral prtns attached to integral prtns 4. On environmental side of membrane a. Glycoproteins and glycolipids – short carbo chains attached to proteins and lipids b. fxn of the carbo “coat” – - Recognition of molecules that interact w/ cell (virus, hormones, antibody) Adhesion process – cell to cell Functions of proteins a. Enzymes b. Transport carriers – allow movement substances across membrane c. Receptor sites – recognition and binding of hormones Variation in cell membrane and cell types • Vary from membrane to membrane and place to place on same membrane • Differences allow for unique properties of cells III Functions of cell membrane • Controls flow of substances in and out of cell • Receives info that permits cell to sense changes in its environment and respond • Maintains structural and chemical relationships w/ neighboring cells • Protects the cell III. Cell Wall Information A. Located OUTSIDE of cell membrane B. Found in: 1. Plants a. Middle lamella 1) Formed as plant cell divides 2) Thin gluey layer between cells (pectin) 3) Holds cells together • B. Primary cell wall – On either side of the lamella – Contains cellulose bundles • C. Secondary cell wall (not always present) – Cannot expand – Lignin is present if the cell’s main function is support- stiffins wall, living material actually dies 2. Algae – wall like plants 3. Fungi – similar but chitin instead of cellulose Prokaryotes – no cellulose, peptidoglycans (amino acids and carbs V. Cell- Cell junctions • A. Plasmodesmata – plant cells – 1. cytoplasmic channels traverse cell walls – 2. 20-60 nm diameter – 3. pathway for water, ions and nutrients – 4. desmotubules – tubular extensions of endoplasmic reticulum B. Gap Junctions • Junctions through which cells can exchange nutrients and molecular communications (sometimes electrical) • Appear as clusters of very small channels (less than 2nm) • Found in muscle cells of heart Before doing this lab you should understand… • Mechanisms of osmosis and diffusion and importance to cells II. Diffusion A. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration B. Small molecules can pass through the cell membrane by a process called diffusion C. Diffusion across a membrane is a type of passive transport because it does not require energy D. This difference in the concentration of molecules across a membrane is called a concentration gradient E. Kinetic energy keeps molecules in constant motion causing the molecules to move randomly away from each other in a liquid or a gas • The rate of diffusion depends on temperature, size of the molecules, & type of molecules diffusing • H. Molecules diffuse faster at higher temperatures than at lower temperatures • I. Smaller molecules diffuse faster than larger molecules • K. Solutions have two parts --- the solute which is being dissolved in the solvent • L. Water serves as the main solvent in living things M. Diffusion always occurs down a concentration gradient (water moves from an area where it is more concentrated to an area where it is less concentrated) N. Diffusion continues until the concentration of the molecules is the same on both sides of a membrane O. When a concentration gradient no longer exists, equilibrium has been reached but molecules will continue to move equally back & forth across a membrane Osmosis • Think back to solutions: solutes and solvents • Osmosis is the process by which water molecules diffuse across a cell membrane from an area of lower solute concentration to an area of higher solute concentration. • Direction of movement depends on relative concentrations of solutions. • http://www.colorado.edu/epob/academics/web_resources/osmosis/ Direction of movement into cells • Hypotonic to the cytosol – solution outside the cell is less concentrated than inside the cell – water moves into the cell • Hypertonic to the cytosol – solution outside the cell is more concentrated than inside the cell – water moves out of the cell • Isotonic – concentrations are equal • http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis. htm Water potential • Definition: measure of the tendency of water to leave one place in favor of another • Important in the study of botany: Why? Water potential equation • Solute potential is zero or a negative # • Pressure potential is zero or a positive # Movement of water into or out of a cell depends on the differences in water potential Ex Try example 1: Potato cell placed into distilled water INITIAL: FINAL: Water potential outside of cell: Water potential outside of cell: Water potential of potato cell initially: Water potential of potato cell at end of observation: Pressure in plant cells is called? • Turgor pressure – keeps veggies crisp • Plasmolysis – loss of water, wilty Determining molarity of potato slices using water potential Equal water potential • Water potential outside of cell when placed in: Unequal water potential Water potential outside of cell: • Water potential of potato cell initially: Water potential of potato cell final: Osmosis- %change in mass (class) Use to Calculate Class Average 1 DW .2M .4M .6M .8M 1M 2 3 AV. Water potential - %change in mass (class average) 1 DW .2M .4M .6M .8M 1M 2 3 AV. PASSIVE VS ACTIVE TRANSPORT • PASSIVE TRANSPORT • No energy (ATP) required! • Molecules/ions move down the concentration gradient – Osmosis – Facilitated Diffusion • Protein Channels • Carrier Proteins • ACTIVE TRANSPORT • Energy required – ATP NEEDED • Molecules/Ions move against the concentration gradient – Protein pumps • Na+/K+ pump – Endo/Exocytosis Active Transport • Endocytosis • Active Transport Movies – see textbook online