Biology week 2-8-16
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This 4 page Class Notes was uploaded by Audrey Notetaker on Wednesday February 10, 2016. The Class Notes belongs to 200001 at Boston College taught by Danielle Taghian in Spring 2016. Since its upload, it has received 29 views. For similar materials see Molecules and Cells in Biology at Boston College.
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Date Created: 02/10/16
Chapter 6: Lipids, Membranes, and First Cells 2/8/16 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
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