Plasma Membranes and Protein Connections
Plasma Membranes and Protein Connections 1005-11
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This 6 page Class Notes was uploaded by Charlene Scavone on Thursday October 2, 2014. The Class Notes belongs to 1005-11 at George Washington University taught by a professor in Fall. Since its upload, it has received 109 views. For similar materials see Biology of Nutrition & Health in Biosystem Engineering at George Washington University.
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Date Created: 10/02/14
93014 Plasma Membranes and Cell Connections The Plasma Membrane Serves Many Functions gatekeeper of the cell transportation structure signaling All Cells Have a Plasma Membrane it separates a cell from its environment it serves as a selectively permeable membrane meaning some substances are allowed access while others are not you need substances in different amounts in different areas for example high amounts of potassium are needed in the cytosol and some organelles need a lot of sodium The Plasma Membrane uid mosaic model allows for the mobility of the components within the membrane components bilayer of phospholipids cholesterol proteins glycolipids and glycoproteins which make the extracellular matrix sticky The lipid bllayer is composed of phospholipids which have hydrophlllc head groups and hydrophobic tails Hydrophlllc portions of a protein are exposed to water on either side of the membrane 03913 of 5quot form channels through which ions and signa ng molcules can enter and leave the cell molecule Receptor proteins receive signals from the environment outside the cell r Some types of transport proteins 1 39739 3939 while hydrophobic g 1 portions remain embedded 39 1 in the hydrophobic core regulated they can be opened l or closed In response to internal or external signals u n39quotr 39 39 39 39 39 39 39 39 39 quot 39 quot39 1 a a a 39 a cl u 1quot quot39 I I I Most transport channels are l 39 39 v p 39 39 a U 39 39 t 39 39 v a I I 4quot andpassthemonto O V 1 39 l I l I I 1 a J J I 1 I 39 u 39 I I I I t 39 392 a I 39 I I I 1 I I 39 I a I 39 I I I a t 1 a Some proteins extend all the way through the 1 J A 7 w only partway Into the bllayer Transport diffusion osmosis passive transport can be facilitated active transport always facilitated membrane involved transport exocytosis and endocytosis Diffusion Diffusion ceases when food coloring molecules are evenly distributed As many Dquotiquotk mix with molecules move into any red f d i 39i 9 given region as leave it so there is no net movement of the molecules 1 At first the molecules of food coloring are concentrated in one region Time l Net movement of the food coloring is from regions of high concentration to regions of low concentration This is diffusion At equiiibiium Initial state Discover Biology 5e Figure 73 2012 W W Norton amp Company Inc movement from an area of higher concentration to lower occurs often wmolecules in a solution so the solute is evenly distributed throughout the solvent rate of diffusion depends on heat concentrations what can diffuse across the membrane small molecules any small lipid and sterolbased hormones any small gas water everything moves through the barrier between spaces Osmosis Isotomc soluuom cells Hypertonic solution Hypotonic solution Cells lose water Cells gain water neither gain nor lose water Total solute concentration Total solute concentration Total solute concentration outside equals total outside exceeds total outside is lower than solute concentration solute concentration total solute inside inside concentration inside Ho Wallless cells can Animal cells gam so much water In a hypotonic solution that they burst Walled cells such as those of plants are Plant Z protected from bursting cells Z in a hypotonic solution because the cell wall restricts continual A p x p W T P X water uptake Discover Biology 5e Figure 75 201 2 W W Norton amp Company Inc passive diffusion of water from an area of lower solute concentration to an area of higher solute the diffusion of water across the plasma membrane isotonic equal amounts of solute on both sides hypertonic one side has more solute hypotonic vice versa water will always move from a hypotonic to hypertonic situation animal cells can burst if they are in an hypotonic solution Passive vs Active Transport concentration gradients areas of abundance to clarity passive transport downhill in energy movement form high concentration to low facilitated channel or carrier proteins active transport requires added energy ATP movement from low to high facilitated carrier proteins channel proteins only allow one or maybe two speci c molecules an important passive carrier is a protein called GLUT active carrier proteins are specific molecules that move across the plasma membrane based on the shape of the molecule require ATP TRANSMEMBRANE TRANSPORT Type oftransport Passive Transport M is Mechanism a Simple diffusion b Facilitated diffusion C Energy input required Molecules slip between Diffusion is facilitated by Active transport is facilitated phospholipids channel proteins or carrier by carrier proteins proteins Outside We 9 g Q 0 hVdquot Phquotquot Water Oxygen Carbon Q Q C 0 a 0 heads dioxide Q 9 lt9 0 O 0 O 3 c f39 39 f n g v 39tquot ai I p 39 J Wu l 1ii 0Q 4 1 I NV 1 39 l V 4 i V o Cvtoplasm 4 Q Energy 0 Types of Molecules such as water Channel proteins ions water Carrier proteins ions molecules that oxygen and carbon canier proteins ions various various charged or typically cross the dioxide small hydrophobic charged or uncharged uncharged molecules membrane molecules molecules Discover Biology 5e Figure 76 part 1 2012 W W Norton amp Company Inc Membrane Involved Transport getting large things out exocytosis EXOCYTOSIS 0 Plasma Ex orted Q o P 30 Q 0 outside membrane substance 0 O of cell Discover Biala 5e Figure 79 2012 W W rton amp Company Inc large molecules are excreted via transport vesticles getting large things in endocytosis pinocytosis cell drinking cell takes on more water from the environment outside of the water phagocytosis consuming a microbe or other object in defense receptormediated endocytosis see below ENDOCYTOSIS 3 Yeast cell LDL particle Cholesterol Fit in plasma membrane cl Mechanism of phagocytosis Bacterium or Pseudopodium food particles Pinocytotic vesicle Discover Biology 5e Figure 710 2012 W W Norton amp Company Inc if too few receptors are produced for LDL cholesterol particles they will stay in the bloodstream and become arterial plaque in many cases of familial hypercholesterolemia high cholesterol can be caused by mutant malfunctioning receptors instead of the LDL docking properly it cannot attach to these receptors and instead oats throughout the bloodstream eventually becoming plaque these malfunctioning receptors are hereditary Protein Connections plasma membrane structures that interconnect adjacent cells are known as cell junctions Vertebrate animals have three types tight junctions are leakproof anchoring junctions latch cells together gap junctions tunnels between cells CELLULAR CONNECTIONS Tightjunctions prevent substances from leaking between cells cells by binding them to each other I Anchoring junctions brace Gap junctions allow ions and small molecules to pass quickly between cells L y Plasma P membranes of adjacent cells Extracellular matrix Discover Biology 51 Figure 711a 1012 W W Norton amp Company Inc Cell Signaling signal producing cells ie steroids or testosterone release small proteins or molecules receiving cells target cells receive the signal other cells have protein receptors specific for that molecule hydrophilic molecules have cellsurface receptors hydrophobic molecules have intracellular receptors 9 5 quot id Outside of cell Activated target gene I I quot V i 1 Vquot quotii quot V 39 i i l 8E D V l 7 Signaling Molecules and Hormones work autocrine on the cell paracrine on neighboring cells endocrine longdistance communication cells can be centimeters to meters apart these signals travel in plant sap and animal blood malformed receptors can disrupt bodily functions by making it so signaling molecules and hormones cannot dock properly as seen with LDL cholesterol above