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BSC 114 Chapter 7 Notes

by: Alexis Elston

BSC 114 Chapter 7 Notes BSC 114

Alexis Elston
GPA 4.0

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About this Document

Complete coverage of chapter 7 taken from in class slideshow and book.
Principles Of Biology I
Daryl W. Lam
Class Notes
Biology, Chapter7, notes
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This 3 page Class Notes was uploaded by Alexis Elston on Monday October 3, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Daryl W. Lam in Fall 2016. Since its upload, it has received 11 views. For similar materials see Principles Of Biology I in Biology at University of Alabama - Tuscaloosa.


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Date Created: 10/03/16
Chapter 7 Membrane Structure and Function  Plasma Membrane: o Boundary that separates a living cell from its surroundings  Consists of phospholipid bilayers that are embedded with many proteins o Hydrophobic fatty acid tails – face inward o Hydrophilic phosphate head – face outward  Other lipids, such as sterols, are also present  Selective permeability – allowing some substances to cross more easily than others o Fluidity: membranes must be fluid to function properly  Phospholipids in a plasma membrane can move within the bilayer  Most of lipids and some proteins drift laterally within the membrane (left and right)  Very rarely “flip­flop” over x axis  As temperatures cool, membranes transition from a fluid to solid state  Lipid Composition: Temperature at which a membrane solidifies  Cholesterol has different effects on membrane fluidity at different temperatures o Warm, cholesterol restrains movement of phospholipids o Cool, helps maintain membrane fluidity by preventing tight packing of  phospholipids  Rich in Unsaturated fatty acids = more fluidity in membrane o Protein Movement in Membranes:  Proteins are much larger than lipids and move more slowly o Lipid Variation:   Variation in lipid composition of cell membranes appears to be adaptations to specific  environment conditions  Change in response to temperature  Plants and membrane fluidity due to altering ratio of unsaturated to saturated FA  Membrane Proteins and Their Functions o Proteins determine most of a membrane’s specific functions  Peripheral membrane proteins:  Bound to the surface of the membrane  Integral membrane proteins:   Penetrate the hydrophobic cores and can span the entire cell membrane o Transmembrane proteins – span entire membrane  Hydrophobic regions of integral membrane protein consist of  one or more stretches of nonpolar amino acids  Often coiled into alpha helices o Six Major Functions  Transport  Enzymatic activity  Signal transduction  Cell­cell recognition  Intercellular joining  Attachment to the cytoskeleton and extracellular matrix o Membrane Carbohydrates  Cells recognize each other by binding to surface molecules, often carbs, on the plasma  membrane  Membrane carbs may be covalently bonded to lipids or proteins  Synthesis and Sidedness of Membranes o Have distinct inside and outside faces  Asymmetrical distribution of proteins, lipids, and associated carbs in the membrane is  determined when the membrane is constructed by the ER and Golgi apparatus  Selective Permeability Chapter 7 o Membrane controls the exchange of materials between a cell and its surroundings  Hydrophobic molecules  Can dissolve in the lipid bilayer and pass through rapidly  Hydrophilic molecules: polar molecules and ions  Cannot diffuse through cell membranes o Transport Proteins:  Allow passage of hydrophilic substances across the membrane  Channel proteins:  o Have channel that certain molecules or ions can use to enter or leave a  cell o Have aquaporins that facilitate passage of water  Carrier Proteins:  o Bind to molecules and change shape too shuttle them across the  membrane  Protein is specific for the substance it moves o Types of Transport  Diffusion: tendency of molecules to spread out evenly into the available space  Diffusion of a population of molecules may exhibit a net movement in one  direction  Passive Transport  Soluble substances diffuse down their concentration gradient  o Higher concentration to lower concentration o No work is required  Osmosis: diffusion of a solvent across a selectively permeable membrane from the side  with lower TOTAL solute concentration to the side with higher solute concentration  Direction of osmosis is determined by difference in total concentration o Osmoregulation: control of solute concentrations and water balance  Facilitated Diffusion:  Use transport proteins to speed up passive movement of molecules across the  plasma membrane  Active Transport: moves solutes against their concentration gradient  Requires energy, usually ATP  Performed by specific transport proteins embedded in cell membranes  Sodium­potassium pump  Cotransport: when active transport of a solute indirectly drives transport of another solute  Plants use gradient of hydrogen ions generated by protein pumps to drive active  transport of nutrients into the cell  Bulk transport:   Requires energy o Endocytosis:  Cell takes in macromolecules by forming vesicles from the  plasma membrane  Three types  Phagocytosis  Pinocytosis  Receptor­mediated endocytosis o Exocytosis  Transport/secretory vesicles migrate to the plasma membrane,  fuse with it, and release their contents to the extracellular  environment  Chapter 7  Many secretory cells use exocytosis to export their  products o Tonicity: ability of a solution to cause a cell to gain or lose water  Isotonic solution: no net movement of water  Concentrations are equal  Hypotonic solution: cell gains water  Solute concentration is less than inside cell  Hypertonic solution: cell loses water  Solute concentration is greater than inside cell  Water Balance of Cells with Walls o Cell walls help maintain water balance in plant cells  Plant cell in a hypotonic solution swell until the wall opposes uptake  Cell is now turgid  If there is no net movement of water into the cell, cell becomes flaccid and plant may wilt  Hypertonic environments make cells lose water   Cell membrane pulls away from wall and usually lethal effect is plasmolysis  Maintenance of Membrane potential by Ion transporters/pumps o Membrane potential is the voltage difference across a membrane  Voltage is created by differences in distribution of positive and negative ions  Electrochemical gradient o Chemical force (ion’s concentration gradient) o Electrical force (effect of membrane potential on ion’s movement) o Electrogenic Pump: transport protein that generates voltage across a membrane  Proton Pump


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