Membrane Structure PDF

Membrane Structure Session Learning Outcomes (SLOs): 1. Outline the components of biological membranes. 2. Describe the properties of the lipid bilayers that compose biomembrane 3. Describe the roles of phospholipids, cholesterol in cell surface membranes fluidity 4. Explain the fluid state of mem...

Membrane Structure Session Learning Outcomes (SLOs): 1. Outline the components of biological membranes. 2. Describe the properties of the lipid bilayers that compose biomembrane 3. Describe the roles of phospholipids, cholesterol in cell surface membranes fluidity 4. Explain the fluid state of membranes and the movement of its lipids 5. Describe the impact of temperature, fatty acid composition, and cholesterol presence on membrane fluidity. 6. Outline the types of membrane proteins. 7. Explain the different ways proteins can be associated with a membrane 8. Explain the movement of the cell membrane proteins. 9. Describe the roles of glycoproteins in cell surface membranes and proved examples of its importance. Phospholipid something that dosen't  e water so well in Fluid Mosaic Model of Biomembrane Fluid Mosaic Model fire form phospholpid by 1- PHOSPHOLIPIDs 2. CHOLESTROL 3. GLYCOLIPIDs 4. Cell Membrane PROTEINs 5 CARBOHYDRATEs Plasma membrane 1.Affect shape and function The circle cell to the cell 2.Anchor protein to the membrane 3.Modify membrane protein activities 4.Transducing signals to the cytoplasm “A living cell is a self-reproducing system of molecules held inside a container – “the plasma membrane” MI.im Membrane comprised of lipid sheet (5 nm thick) nt Primary purpose - barrier to prevent cell contents spilling out BUT, must be selective barrier  Eukaryotic membrane are dynamic, fluid structures and most of their molecules move in the plan of the membrane Stacked membranes of Golgi complex  General Structure All biological membranes have a common structure Thin film of lipid and protein molecules held together by noncovalent interactions  mid 1- PHOSPHOLIPIDs In The most abundant membrane lipids are the phospholipids 0 Phospholipid have a polar head (H2O loving) group and two hydrophobic hydrocarbon tails (H2O hating) The tails are usually fatty acids, and they can differ in length. as One tail usually has one or more I cis-double bonds, while the other _Iomef does not. m  Amphipathic Molecules Émen hydrophobic Contain both a hydrophilic and a hydrophobic portion to the molecule Im Other molecules are amphipathic – Steroids – Glycolipids – lipid with a sugar attached rather than a phosphate group  Hydrophilic and hydrophobic molecules interact differently with water Hydrophilic molecules can dissolve in H2O due to the polarity of both of these molecules – H bonds and other non-covalent interactions may aid in this  Hydrophobic molecules will be “caged” by the polar molecules – requires energy Why when fats or oils are placed in water that they usually sit as a glob on the surface The Lipid Bilayer molecules has two Parts many head Membrane lipids are amphipathic molecules, most of which a __ spontaneously form bilayers listhichy Phospholipid bilayers: two molecule thick, formed the cell membrane Two important of lipid bilayers: 1. Hydrophobic core: prevent the diffusion of water-soluble molecules. It regulated by specific membrane proteins. 2. Stability by hydrophobic and van der Waals interactions between the lipid chains.  The spontaneous closure of a phospholipid bilayer to form a sealed compartment am 00 g stable The formation of aÑsealed compartment u is fundamental to the creation of a living cell, and this behavior follows directly from the E shape and amphipathic nature of the phospholipid molecule The shape and amphipathic nature of the lipid molecules cause them to form bilayers spontaneouly in aqueous environments. i hallow formwhenlibid in moleculespresent lowconcentration only one layer to deliver Ms phosphobic Vaccines tool drugs or system Due to the amphipathic nature of phospholipids, these of delivery molecules spontaneously assemble to form closed bilayers Packing arrangements of lipid molecules in an aqueous environment 9 9 ax 809 wh's Lipid molecules spontaneously aggregate to bury their hydrophobic do tails in the interior and expose their hydrophilic heads to water. Being cylindrical, phospholipid molecules spontaneously form bilayers in aqueous environments  what Membrane proteins can be solubilized and purified in detergents Detergents: Éf Used to remove the proteins from the membrane Amphipathic molecules Have a single hydrocarbon tail I Form small clusters in aqueous solutions called micelles SDS and Triton X-100 common in the laboratory c  to gisyj.be the cell membrane Structure and function of detergent micelles it has the same structure as the hosplopic Solubilizing membrane proteins with a mild detergent I traces G intracellular The use of mild detergents for solubilizing, purifying, and reconstituting functional membrane systems Formation of and study of pure phopholipid bilayer A Phospholipid spontaneously form bilayers - Liposomes can be used to carry membrane impermeable substances into cells. 1- Water-soluble substances (e.g., proteins, nucleic acids, drugs) can be encapsulated into liposomes. 2- Liposomes can fuse with cell plasma membranes (a lipid a bilayer), releasing substances into cells (can be used as drug delivery tools). 3-Liposomes are used as model systems to study membrane permeability (or membrane protein reconstitution). 088k se 0  Arrangement of Phospholipids in Membrane cells Amphipathic molecules have both components so the hydrophilic head molecules interact with the aqueous solution and the hydrophobic tails will interact with each other qnqqqo.fi a Outside of cell Carbohydrate chains Proteins phospholipid bilayer Transport Phospholipids Protein Inside of cell (cytoplasm) Lipid composition and structural organization Three major classes of lipids are found in the lipid bilayer: bsPhospholipid Or Cholesterol Glycolipids 2. CHOLESTROL only in animals Eukaryotic plasma membranes contain large amounts of cholesterol It is found in the cell membranes of animals but not plants. It affects the fluidity of the membrane.  Cholesterol in the Membrane Cholesterol is added to areas that have lots of unsaturated lipids to help fill in the gaps between the tails Helps to stiffen and stabilize the bilayer – Less fluid – Less permeable destroy Q Figure 11-16b Essential Cell Biology (© Garland Science 2010)  If 3. GLYCOLIPIDs Glycolipids are found on the surface of all plasma membranes Glycolipids are found only on the non-cytosolic surface – Sugar added in the Golgi Apparatus. T.IT Lipid bilayer asymmetry Two layers of bilayer have different compositions - Different phospholipid/glycolipid inside vs outside orientation F - Membrane proteins embedded into membrane with specific glycolipid Phosphatidylcholine (PC) Sphingomyelin (SM) Phosphatidylserine (PS) Phosphatidylinositol (PI) Phosphatidylethanolamine (PE) The asymmetry of the lipid bilayer is functionally important  twodifferent y structure Lipid bilayer asymmetry - Membrane synthesis occurs in endoplasmic reticulum (ER) New membrane exported to other membranes by vesicles (budding and fusion) his occurs during manufacture - Lipid asymmetry - To permit membrane growth, newly synthesized membrane must be _fo evenly distributed between both monolayers layertotheoathegginagining this fan hathdpsselectivdyermsfrspesfichipidsfromneyoofthe.fi - Flippases selectively transfer specific phospholipids ⇒asymmetric distribution in each monolayer Toda  HE Phospholipid mobility Cell membrane move diffrent m.tt ntstPhopholipid enzym 0 yffgfiiiiiif.com The two leaflets of a bilayer membrane tend to differ in their lipid composition. needs spesficenzy.ms Flip-flop of lipids (from one half of a bilayer to the other) is normally very slow. My grakeletto Flip-flop would require the polar head-group of a lipid to traverse the hydrophobic core of the membrane. Need large energy so Some membranes contain enzymes that actively transport particular lipids from one monolayer to the other. Flippases catalyze flip-flop in membranes where lipid synthesis occurs. speed up  being synthesizedensuring Lipid bilayer asymmetry prgpefhip.iq Faces of cellular membranes are conserved during membrane budding and fusion tm Endocytosis: red membrane is face to cytosol Exocytosis: red membrane is also face to cytosol Entities (exoplasmic face) cytosolic ineelayiaym.my cities the phgocytos.is Thedigramshowsavesicle formingthrough endocytos The hgytosolicsegm I surfu Gas see cytosolic  phospholipids an Inositol phospholipids are only on the cytosolic surface – Functions to relay signals on cytosolic surface that pass through the membrane ii E ii Tf Signaling functions of inositol phospholipids in the cytosolic leaflet of the plasma membrane iii iti  these cos gaga Lipid rafts byhighlyorder GEOplasm it Lipid rafts are small specialized areas in membranes where some 80 lipids (primarily sphingolipids and cholesterol) and proteins are concentrated Plasma membrane contains lipid in ceriten rafts that are enriched in sphingolipids, cholesterol, and erees some membrane proteins  Lipid rafts iemomicrodomia Cholesterol and sphingolipids cluster with specific proteins in membrane microdomain aeit.o 5300 solubilization, which has Lipid rafts are resistant to detergent facilitated their isolation and characterization. Lipid rafts are enriched for may receptors, signaling proteins what arelipid rafts IIIiii IiiIII Iiiiiiiiiii whyaretheyimportant tl mPaigi ceptors iiiiiiiiiiiiiiiiiiiiii.EE whatisdetergent resistance  allows lecules ee y Membrane fluidity spread evenly whysholudthemembranebefluid themembraneneedstobefluidsothatmolecule is it r inieanes fits Paleteinana canmovearoundwithinit Helpswithproteinmovement Why does membrane need to be fluid? Afluidmembraneallowsproteinstomovequickly igniting.ineepisieinieta in snatien recivemessages i - Enables rapid diffusion of membrane proteins within plane of bilayer and permits interaction (important for cell TIL.cc Distributesnew molecules signaling) tothe or for are when new added lipids proteins membrane example - Facilitates distribution of membrane lipids and proteins from insertion site (following synthesis) to other regions of allowsmembrane cell tofuseandmix fluidityhelps t.us m embranes togetherw hen needed Eiganding Eating ca's property ribation Ethan - Allows membranes to fuse and mix molecules Firing iii.isiiiiiiE ii - Ensures even distribution of membrane molecules between daughter cells following cell division  The factors that can affect the fludity Mobility of a given membrane components depends on: L - Phospholipid composition and its interactions with other molecules - Temperature - Lipid composition (tails, cholesterol)  more solid less fludity saturated phospholipid composition Close packing of hydrocarbon tails ⇒less fluidity (increased viscosity) fattyatta chains Length and unsaturation determine closeness of packing 8 58544 Length varies from 14-24 C atoms; shorter chain length ⇒less interaction ⇒increased fluidity miles idity GEE One tail of molecule has one or more double bonds - unsaturated (H atoms); other tail has no double bonds - saturated Double bonds ⇒kinks ⇒less packing  9 Insummary doublebonds infattyacid chainreducethenumberof vanderwaalsinteractionsmaking themembranemorefluidfewer doublebonds asinsaturatedfats Leadstomoreinteractions making themembranelessfluidandmore solide Van der Waals interactions between fatty acyl chains are the main determinants of acyl chain mobility. Double bonds reduce the number of potential van der Walls interactions between fatty acyl chains  more fludity 9 The membrane becomes more difficult to freeze so if the hydrocarbon chains are short or have 0 double bonds, so that the membrane remains iii fluid at lower temperatures bonds unstauratedmakethe membranemore isbecausethe fluid.This with double 2191921 Stag's ftp.igsfgefhg.us Whenthemembrane hasthesekindsofchains it Thiskeepsthemembranefluidevenat EFreeze bey.FI Temperature thierature fitting Gel and fluid forms of the phospholipid bilayer Heat disorders the nonpolar tail and induces a transition form gel to fluid Cholesterol will regulate the fluidity of the membrane debriding on th satuart andunsatural Cholesterol is important in maintaining the fluidity Phospholipids Cholesterol Functions in 3 ways: Geeties Bing's.be2onFro9Ei'swatPdps8iPidsThis makesitharder forsmane ssbfnfjightdebidingrathh.my It can weakly bind to hydrocarbon tails making it more difficult for smaller molecules to cross membrane. 2. It maintains the fluidity and increases the stability of the membrane. If the phospholipids are saturated, it prevents them from being packed too closely, making the membrane more fluid The role of chol not to stole tell the gap depends on the structure but to of the the take phospholipids tails for satyffedother 3. If the phospholipids are unsaturated there are kinks in the tails where the cholesterol molecules can fill in and anchor them making the membrane less fluid. 4- Cell Membrane PROTEINs Membrane proteins can be associated with the lipid bilayer in various ways: 10 jan integral Frotein attached Protein onlyone to yÉmiÉÉ i in is Figure 10-17. Molecular Biology of the cell 6e (Garland Science 2015) Peripheral Proteins whatarethe integralmembraneprotiens Transmembrane Proteins Interaction with transmembrane span the entire membrane proteins 48 Also called integral membrane proteins Linked by lipids on either surface of the membrane  Membrane Proteins iilII iiiiiiTI.IE IIIIIIII Membranes contain specific proteins to mediate their distinctive functions. Theyspan themembrane iii iiiiiiiii Figure 11-20 Essential Cell Biology (© Garland Science 2010) Carry out the functions of the membrane – Transporters – Na+ pump to move Na+ across – Linkers – integrins to link intercellular components to extracellular ones – Receptors – to bind a compound that sends a signal to the rest of the cell – Enzymes – perform chemical reactions in the membrane  Peripheral Membrane Proteins doggie dineteansmeman ET.tn GgiIr Protiens Proteins that are attached to either surface of the bilayer monovalent e w ̅ Those attached to lipids are covalently linked Those that interact with other transmembrane proteins are attached by noncovalent interactions without Eels in themembraneembedding covalente Noncovalentbond protien Prot Prot Protie  I iii proves that Protein Movement Feiian so Proteins can move through the layer of the membrane similar to the lipids Can’t flip from one side to the other Many membrane proteins diffuse in the plane of the membrane Frop 809 This experiment helps Thelight comes L Fluorescence recovery after photobleaching (FRAP) 5 M n  glowing me Fluorescence loss in photobleaching  Restriction by Location Protein Theroof Iiiii Function ation p Keatre.PE fasn they test 0 The Es floor Apical side – facing opening Basal side – bottom of the cell attacan Lateral sides – side surfaces  Membrane Domains Cells can restrict the movement of proteins by: can Egg 0 0 iiive sidescans sayoy si92othe iii.ie Qg Cell cortex attachment Interaction with Cytoskeleton meat EE jo thoces Extracellular attachment together Attachment to other cells Four ways of restricting the lateral mobility of specific plasma membrane proteins the sperm If their own Three domains in the plasma membrane of a sperm cell Many membrane proteins are glycosylated and have intrachain or interchain disulfide bonds 0 inside the D protein pistett most Protiensof the the Glycoprotein on integrnel are Protein strong Sugars handshakes i Inese sugars help the talkto otherprotein or do cells jobsimportant  5- CARBOHYDRATEs Some phospholipids have carbohydrates attached to them – GLYCOLIPIDS Some of the proteins have carbohydrates attached to them – GLYCOPROTEINS Many of the plasma membrane proteins have sugars attached to them – – TWITSI Short oligosaccharides – glycoproteins Long polysaccharides - proteoglycans important to keep Sugars on the surface make up the glycocalyx cell surface the – Keeps cells moist and slippery 51 Is huming – Used as cell recognition (lectins) and adhesion molecules helpsthe cellsrecognize andtalkto eachother kind oflike name tags thatlet them knowwhos's who  A simplified diagram of the cell coat (glycocalyx) is_ glycocalyx  so The role of glycoproteins They may help in the recognition of, and interaction with, other cells. They may also play a part in the recognition of t hormones and foreign molecules. The cell coat, or glycocalyx is the carbohydrate-rich zone on the cell surface Likely functions – It protect cells against mechanical and chemical damage keep foreign objects and other cells at a distance  channel protien apftfien 1- Transport proteins Channel proteins: function by having a hydrophilic channel 1hfh1gsh.tw aterything that certain polar molecules or ions use as a tunnel Carrier proteins: function by holding onto their passengers the and change shape in a is Chang way that shuttles them s across the membrane hedrophilic  o 2- Attachment to the cytoskeleton and extracellular matrix. 3- Receptor site-Ex. Insulin never goes into a cell but binds to a receptor site on the cell membrane imagine thecellhas a mailbox some insulindon'tgointothe things like cellbuttheysend amessage something inthe mailbox byputting this helps 4- Enzyme-Some proteins in the know the cell what membrane may expose their spending active site to speed up a door chemical reaction. 5- Intercellular joining (adhesion) holding hands 6- Cell to cell recognition (glycoproteins). name tags  Summary 1. Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER. 2. Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads. 3. The best model of the cell membrane is called the FLUID MOSAIC MODEL. 4. The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent). 5. Proteins can float or be fixed and also have hydrophobic and hydrophilic portions. 6. Some proteins and phospholipids have carbohydrates attached to them to form GLYCOPROTEINS and GLYCOLIPIDS.  7. Phospholipids form the bilayer, act as barrier to most water soluble substances. 8. Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane. 9. Proteins act as transport proteins to act as channels for substances to move into or out of the cell. Some act as membrane enzymes and some have important roles in membranes of organelles. 10. Glycolipids and Glycoproteins help to stabilise membrane structure, some act as receptor molecules eg for hormones and neurotransmitters or as antigens for other cells to recognise them.