Biology 2170, Week Four Notes
Biology 2170, Week Four Notes BIOL 2170 - 002
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BIOL 2170 - 002
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This 3 page Class Notes was uploaded by Katie Veselka on Tuesday September 20, 2016. The Class Notes belongs to BIOL 2170 - 002 at University of Toledo taught by Robert M. Stevens in Summer 2016. Since its upload, it has received 8 views. For similar materials see Fundamentals of Life Science: Biomolecules, Cells, and Inheritance in Biology at University of Toledo.
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Date Created: 09/20/16
Lecture 6: Cell Membranes 09/14/16 A) Biological Membrane Structure a) General structure is known as the fluid mosaic model b) The phospholipid bilayer is like a “lake” in which proteins “float” I) Phospholipids had hydrophilic and hydrophobic components c) Artificial bilayers can be made in the laboratory d) Lipids maintain a bilayer organization spontaneously I) Helps membranes fuse during exocytosis B) Composition a) Membranes may vary in lipid composition b) Phospholipids vary from lipids as they have a polar head and two fatty acid tails c) Membranes may be up to 30% cholesterol d) Phospholipid bilayer is flexible and the interior is fluid, allowing lateral movement of molecules e) Fluidity depends on what types the membrane is made of I) Lipids II)Cholesterol (temperature) C) Carbohydrates in Membranes a) Membranes that have carbohydrates on the outer surface that serve as recognition sites for other cells and molecules I) Glycolipids II)Glycoproteins D) Membrane Proteins a) Types I) Integral Membrane protein (1) Are typically transmembrane proteins (i) Span the bilayer, hydrophilic ends protrude on either side (2) Peripheral membrane proteins (i) Temporarily associated with either the internal or external side of the membrane b) Protein Anchoring I) Some membrane proteins can move freely within the bilayer, while some are anchored to a specific region II)Some can be anchored by cystoskeletal elements IIISome by lipid raft-- a defined patch of membrane with distinct components E) Membrane Transport a) Membranes have selective permeability I) Some substances can pass through, but not others b) Passive transport I) Works by diffusion-- random movement of molecules toward equilibrium (1) Diffusion leads to a net movement of the substance from one region to another when there is a concentration gradient (2) Moves from an area of high concentration into an area of low concentration (3) Net movement is directional until equilibrium is reached (4) Equilibrium—particles continue to move, but there is not net change to distribution (5) Diffusion rate depend on (i) Concentration difference between two sides of membrane (ii) Permeability of the membrane (iii)The temperature of the solution (6) Diffusion works very well over short distances (7) Membrane properties affects the diffusion of solutes (8) The membrane Is permeable to solutes that move easily across it; impermeable to those that can’t (9) Simple diffusion (i) Water also diffuses across the membrane (ii) Electrically charges and polar molecules can not pass through easily II)Osmosis (1) Diffusion of water from region of higher water concentration to region of lower water concentration (2) Osmosis depends on the number of solute particles present, not the type of particles (3) Solution types (inside vs. outside of cell) (i) Isotonic: equal solute concentration and equal water concentration (ii) Hypertonic: greater solute concentration (iii)Hypotonic: smaller solute concentration (4) Water will diffuse from a hypotonic solution across a membrane to a hypertonic solution (5) Animals cells may burst when placed in a hypotonic solution (6) Plant cells with rigid cell walls build up internal pressure that keeps more water from entering (i) Called turgor pressure IIIFacilitated diffusion of polar molecules requires carrier proteins (1) Channel proteins have a central pore lined with polar amino acids (2) Carrier proteins are membrane proteins that bind some substances and speed their diffusion through the bilayer (i) Transport polar molecules such as glucose across membrane in both directions (ii) Glucose binds to the protein which causes it to change shape and release glucose on the other side (3) Ion channels are integral membrane proteins that form channels (4) Most are gated (i) Can be open or closed to ion passage (ii) Gate opens when protein is stimulated to change is shape (5) All cells maintain an imbalance of ion concentrations across the plasma membrane thus a small voltage potential exsists (6) Rate and direction of ion movement through channels depends on the charge of the ion IV)Water entry (1) Water can simply diffuse across a membrane (2) Or it can move through special water chambers called aquaporins c) Active transport—movement of substances across the membrane against the concentration and/or electrical gradient I) Requires energy II) Cells move substance through transport proteins embedded in the cell membrane III)Primary active transport requires energy directly from ATP (1) Sodium-potassium pump is an example of primary active transport IV) Secondary active transport energy comes from an ion concentration gradient that is established by primary active transport (1) Uses energy available from the concentration gradient of another molecule (2) Aids in uptake of amino acids and sugars
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