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Chemistry week of 2-8

by: Audrey Notetaker

Chemistry week of 2-8 111001

Marketplace > Boston College > Chemistry > 111001 > Chemistry week of 2 8
Audrey Notetaker
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Chapter 12: Colligative Properties of Solutions, Colloids and Detergents
General Chemistry II
Neil Wolfman
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This 7 page Class Notes was uploaded by Audrey Notetaker on Friday February 12, 2016. The Class Notes belongs to 111001 at Boston College taught by Neil Wolfman in Fall 2016. Since its upload, it has received 30 views. For similar materials see General Chemistry II in Chemistry at Boston College.


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Date Created: 02/12/16
Chapter 6: Lipids, Membranes, and First Cells  2/8/16­2/12/16 Lipids and Membranes  Plasma membrane: protein containing lipid bilayer surrounding cells o Separates life inside vs outside of cell o Regulates the passage of molecules and ions into and out of the cell; selective  barrier   Hydrophobic/non polar molecules will pass more easily  Hydrophilic/polar/large molecules won't pass easily so proteins in the  membranes help facilitate them passing o Has a polar phosphate head and a non­polar fatty acid chain  How do membranes Help life o Enable different internal and external solutions o Help localize and bring together reactions that otherwise wouldn't occur; more  efficient also maximized o Localized specific functions  What is a lipid o Lipid: major hydrocarbon component which are normaly nonpolar and  hydrophobic; length varies and impacts the fluidity  Isoprene: hydrocarbon chain  5'C carbond  Fatty Acid: hydrocarbon chain bonded to a carboxyl group formed by  adding 2 carbon subunits  Carboxyl group is why it's called a fatty acid  Types of Lipids o Isoprene chains ­ have a methyl group sticking out  Steroids (chelesterol)  Amphipathic  Have a four ring structure made from isoprene subunits  Vary by different R groups  Cholesterol important in plasma membrane  Starting point for synthesis of estrogen, progesterone, and  testosterone  Phospholipid:   Glycerol group reacts with phosphate group has two isoprene  chains or two fatty acids   Amphipathic: has a hydrophilic (polar) head, and a hydrophobic  (nonpolar) tail o Fatty Acid ­ no methyl group  Fats  Fats formed from dehydration synthesis  Fats from glycerol linked by ester linkages to three fatty acids  Ester Linkage:   Phospholipid (serine)  Glycerol group + phosphate group o Most lipids have two chains o Phospholipase C can detach the phosphate head from the hydrocarbon component  Bonding/saturation o C double bond  Cis ­ has kinks in it, same side  Kinks help the fluidity of membrane  Trans ­ all hydrogens are on opposite side; not many kinks o Unsaturated/short: have double bonds (oil)  Permeable, liquid at room temperature o Saturated/long: max amount of hydrogens attached to carbon (butter)  Less permeable, solid at room temperature o Unsaturated lipids are better for membranes (better fluidity)  Membranes form spontaneously because of entropic forces (hydrophobic force) which is  the energy that causes the bilayer so nonpolar part is away from the polar water and polar head group is by water. The nonpolar acyl chains are then further stabilized by van der  Waals between the closely packed acyl chains (stronger forces with longer/larger  molecule)  Membrane formation o Liposome: bimolecular phospholipid layer with fluid filled inner cavity, like a  sphere o Micelle: single layer, all chains are in the middle with phosphate on the outside  (detergent); long single fatty acid chain; has a single fatty acid chain vs two o Bilayer:   Selective permeability o Permeability: tendency to let a substance cross  High to low permeability: hydrophobic, small uncharged, large uncharged, ions  Size and charge affect the rate of diffusion across membrane o Phospholipids have selective permeability  Small/nonpolar molecules move across quickly/easily without much if any help  Charged, large, or polar molecules cross slowly and need help (facilitated  transport) o Temperature affects membrane fluidity and permeability  Fluidity decreases with temperature because molecules move more slowly  Decrease membrane fluidity = decreased permeability ­ not  capable of supporting biochemical reactions  Fluidity: phospholipids are in constant lateral motion but rarely  flilp to the other side of the bilayer, movement laterally is fluidity Kinking in fatty acid chain pushes things away, opening more space, allowing for more fluidity *In eukaryotic cells, cholesterol influence permeability by reducing membrane fluidity  Increasing the concentration of C­H bonds increases van der waals decreases fluidity  Making a fatty acid shorter can increase fluidity Fluid mosaic model  Membrane structure is composed of o A mosaic of phospholipids with different types of proteins in it   Transmembrane protein span the entire bilayer (go through and through) o Fluid/dynamic membrane  Predictions of model o Bimolecular sheet of 2 monolayers of lipid. Hydrophobic chains inside and  hydrophilic on the outside o Fluidity (mobility of lipids) is only lateral and rotational; lipid cannot flip from  one monolayer to the other because of the polar head. Low temperature decreases  fluidity  Could tag a protein and watch it move  Mix mouse cells and human cells to fuse them o Bilayers are asymmetric in nature ­ different on both sides depending on what is  attached to the bilayer (different proteins and lipids) o Membrane proteins are either integral (through and through) or peripheral (only  on the outside) Membrane proteins tend to be heavily glycosilated   Integral: span lipid bilayer, have three domains o Extracellular (polar and charged amino acids) o Intracellular (nonpolar and small charge amino acids) o Transmembrane ­ composed of at least 20 non­polar amino acids and adopts an  alpha helix  Single pass protein goes through membrane once  Glycoproteins: carbohydrates attached to protein o O­linked (ser/thr); carbohydrate attached to O o N­linked (asn); carbohydrate attached to N o Glycophorin A is in red blod cells  Types of proteins: transmembrane, membrane associated, lipid linked, protein attached o Move laterally in the membrane and more slowly; don't flip flop Passive Transport: does not require an input of energy, can be diffusion or protein­facilitated  down a concentration gradient (goes from high concentration to low concentration)  Ion channels: specialized membrane proteins for specific ions which allow small, charged compounds allowing them to diffuse through membrane. Different channels for different  ions o Gated channels: open or close in response to binding of a specific molecular or to  an electric charge  Aquaporins/water channels: open/close in response to membrane depolarization or  binding of a regulatory molecule. Only moves water  Carrier proteins  Passive (facilitated) transport of solutes via carrier proteins o Requires no energy (ATP) or electrochemical gradient o Dependent on concentration difference across membrane (inside vs outside);  distribution ratio is less than 1 o Protein mediated (specialized for specific compounds) o Faster than simple diffusion o Highly stereo­specific/highly selective for subsrate recognition  Glucose carrer recognizes D­glucose, but not L­glucose, and transports D­ mannose or D­galactose to a minor degree o Saturation is a sign of the use of facilitated diffusion (can only go at a certain rate) Active Transport: requires energy across membrane against a concentration gradient (going from low to high concentration)  Establishing sodium electrochemical gradients by active transport o Sodium potassium pump: pumps sodium out and potassium in using ATP  Maintains resting potential across membrane; electrochemical gradient of  sodium and potassium across membrane  Regulates cell volume  Contributes to active transport of solutes  Needs 1/3 of ATP to function and 2/3 of ATP for neurons  "pump" is only used for active transport; passive transports are "channels" Diffusion: molecules or ions diffuse across a phospholipid bilayer from an area of high to low  concentration (down concentration gradient). Will always be linear with respect to concentration Sodium potassium ATPase pump establishes electrochemical ion gradients across membranes  that allows other membrane proteins to carry out "active" functions (such as glucose).   Gradient across membrane has a large potential energy  Glucose transport is coupled with sodium which is how it gets into cell (without ATP) o Glucose can get through membrane without pump but sodium needs it Van Gogh: maybe prescribed digitalis ATP hydrolysis to make drugs ineffective in cells (one way as to how tumor cells are resistant to  chemotherapy drugs)    


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