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Transcript
Cells and Their Environment Cell Membrane Structure & Function Cell membrane • Maintains homeostasis • Controls movement into and out of the cell • Support • Selectively permeable- allows some materials through but not others. • Made of 2 groups of organic molecules: • 1. Phospholipids • 2. Proteins Phospholipid • Molecule with a polar head and a nonpolar tail. • Polar head attracts water and nonpolar tails repel water. • Phospholipids form a bilayer. • Phospholipid Bilayer Lipid Bilayer • Fluid like a soap bubble • Does not let many molecules in and out Cholesterol • Embedded in lipid bilayer • Gives bilayer strength Proteins • Allow materials to pass through membrane • Called cell surface proteins 3 types of cell surface proteins • 1. Channel proteins- proteins that let sugars, amino acids, ions to pass through – aka Transport proteins or carrier proteins • 2. Receptor proteins- transmit information from outside to inside • 3. Cell surface markers- identify the type of cell Fluid Mosaic Model of Cell Membrane Fluid=flexible from lipid bilayer Mosaic=Proteins arranged in bilayer Moving Material In & Out of Cell 2 ways: Passive and Active Transport Passive Transport: • Movement of substances across membrane without using energy • Equilibrium-when a concentration of a substance is the same throughout a space. • Solute- substance dissolved in another ex-sugar • Solvent- substance that dissolves the solute ex-water • Solution- mixture of solutes and solvents Types of Passive Transport 1. Diffusion • Movement of particles from an area of high concentration to low concentration until equilibrium is reached. Uses no energy. • Concentration gradient: the difference of concentration of a substance through a region. Diffusion goes with the concentration gradient. Example of Diffusion • Open a bottle of ammonia. Molecules move from high concentration to low concentration outside the bottle until they are spread out evenly. Example in cells • In blood cells in your lungs when you inhale there is a higher concentration of oxygen in your lungs than in your blood. Oxygen diffuses into your blood from a high concentration to a low concentration. 2. Osmosis • The movement of WATER molecules from high concentration to low concentration. • https://www.youtube.com/watch?v=HqKlL m2MjkI Hypertonic • A solution with a higher concentration of solutes than the solution across the membrane. • Water will move into the high concentration of solutes. –Picture on board Isotonic • Equal solute concentration on either side of the membrane. • Equal amounts of water will move between membrane • Picture on board. Hypotonic • A solution with a lower concentration of solutes than across the membrane • Water will move out of the low concentration of solutes. • Picture on board. 3. Facilitated Diffusion • When substances move from high to low concentration through channel proteins. • (3rd type of passive transport) Active Transport • Use energy to transport material across membrane • Uses energy because goes from region of low concentration to high concentration. Types of Active Transport 1. Endocytosis- active transport that moves large particles into cell membrane • 2 types• Phagocytosis- cell eating • Pinocytosis-cell drinking 2. Exocytosis- active transport that moves large particles out of cell 3. Molecule Transport “Pumps” • Used to transport sodium, potassium , and calcium against the concentration gradient. • Uses lots of energy. • Occurs in nerve cells Other cell membrane functions: Cell Communication • Cells communicate by using receptor proteins. • The receptor protein receive messages through hormones, neurotransmitters, voltage Immune system • Cell membranes also help to recognize foreign antigens (germs). • http://www.sciam.com/article.cfm?articleID =0001998E-5F5A-1C749B81809EC588EF21 • http://www.usd.edu/~bgoodman/Lipidsand Diffusion.html#Lipids • http://www.jdaross.mcmail.com/cell2.htm