Cell Membrane: The Fluid Mosaic of Lipids and Proteins
The cell membrane is a thin, elastic structure that surrounds and envelops the cell. It is composed mainly of proteins and lipids, forming a 2
- Uploaded on | 3 Views
- anirudh
About Cell Membrane: The Fluid Mosaic of Lipids and Proteins
PowerPoint presentation about 'Cell Membrane: The Fluid Mosaic of Lipids and Proteins'. This presentation describes the topic on The cell membrane is a thin, elastic structure that surrounds and envelops the cell. It is composed mainly of proteins and lipids, forming a 2. The key topics included in this slideshow are . Download this presentation absolutely free.
Presentation Transcript
Slide5CELL MEMBRANECELL MEMBRANE - is a 2-dimensional fluid mosaic of lipids and proteins and also is in constant motion . - It’s a thin, elastic structure , ~7.5 nanometers thick and envelops the cell. - Composed mainly of proteins and lipids. - Basic structure is a lipid bilayer - a thin film of ~ 2 molecules thick and continuous over the entire cell surface.
Slide6CELL MEMBRANE- Lipid bilayer is made of 3 types of molecules ; 1. PHOSPHOLIPIDS 2. CHOLESTEROL 3. GLYCOLIPID.
Slide7Cholesterol
Slide8iii) GLYCOLIPIDs -are lipids with attached carbohydrate groups ~ 5% of membrane lipids - Non-polar parts - are the fatty acid “tails ” - Polar parts - are the attached carbohydrate groups - Only appear on membrane layer that faces extra-cellular fluid (one reason for the asymmetry of the two sides ).
Slide9Asymetrical Distribution of LipidsModified from Figure 11-17, Page 355 from: Essential Cell Biology by Alberts et al. 1997, Garland Publishing Inc. New York, NY Extracellular Intracellular
Slide10Cholesterol can fill gaps betweenphospholipids Modified from Figure 11-16 and Panel 2-4 from: Essential Cell Biology: An introduction to the Molecular Biology of the Cell by Alberts, Bray, Johnson, Lewis, Raff, Roberts and Walter 1997, Garland Publishing Inc. New York, NY Saturated FA’s = increase in fluidity
Slide13MEMBRANE PROTEINS1. PERIPHERAL PROTEINS Are membrane proteins that are located on the periphery of membranes and they are either on the cell surface or on the inside of cell They associate with membrane lipids or integral proteins at inner or outer surface of the membrane. They can be stripped away from membrane by methods that do not disrupt membrane integrity FUNCTION 1. As enzymes on cell surfaces 2. As regulatory portions of ion channels and transmembrane receptors 3. Roles in cell signaling – by some reversible attachment of proteins on cell surface
Slide14Membrane Proteins
Slide15•The proteins in the plasma membrane may provide a variety of major cell functions. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.9
Slide18PROPERTIES OF CELL MEMBRANES- 2 main properties are; 1. FLUIDITY 2. SELECTIVE PERMEABILITY
Slide19PROPERTIES OF CELL MEMBRANES1. FLUIDITY – (2-dimensional fluid in constant motion) SIGNIFICANCE : - Allows for fusion of membranes (e.g. fusion of vesicles with organelles) - Allows for diffusion of new lipids and new proteins laterally, so they are equally distribution - Allows for diffusion of proteins and other molecules laterally across the membrane in signaling/reactions - Allows for proper separation of membranes during cell division
Slide20PROPERTIES OF CELL MEMBRANES - FLUIDITY MEMBRANE FLUIDlTY is determined by; 1. LIPID COMPOSITION 2. TEMPERATURE
Slide21Phospholipids
Slide22Cholesterol
Slide23Cholesterol
Slide24PROPERTIES OF CELL MEMBRANES -FLUIDITY 2. TEMPERATURE Organisms regulate lipid composition (thus membrane fluidity) in response to temperature . Cold/ low temperatures – membranes “gel” and are not fluid. Hot/ high temperature – membranes are too fluid and become “leaky” allowing ions to cross. Hibernating animals incorporate more unsaturated fatty acids (fatty acids with double bonds) to prepare for drop in their body temperature .
Slide25PROPERTIES OF CELL MEMBRANES -SELECTIVE PERMEABILITY 2. SELECTIVE PERMEABILITY OF MEMBRANE – they are selective for the movement of molecules across the membrane. MOVEMENT OF MOLECULE across membrane is limited by; i) SIZE - small molecules cross membrane and large molecules do not E.g. Water, O2, CO2, ethanol (46 MW) and glycerol (92 MW) can cross the membrane - Glucose (180 MW) can NOT cross membrane ii) POLARITY - Hydrophobic molecules can “dissolve” in the lipid bilayer, not polar molecules. E.g. Ethanol is more hydrophobic than glycerol so crosses membrane faster iii) IONIC CHARGE- – membranes are highly impermeable to ions But ions and large molecules do pass across biological membranes – through proteins that pass through membranes ( integral proteins – channel/transport protein )
Slide2715.1 A pure phospholipid bilayer actsas a selectively permeable barrier Figure 15-1
Slide30Membrane Transport• Simple Diffusion - 2 types of molecules 1. Small, nonpolar • Oxygen 2. Small, polar, noncharged • H 2 O (some - more later) • Ethanol
Slide31Water Channels- The aquaporinsH 2 O H 2 O HO H HO H 2 O Aquaporins • Selectivity filter generated by hydrophobic residues that line the channel allowing only one molecule of water to pass at a time
Slide34Membrane Transport
Slide36Ion Channels-small aqueous holes • Properties – selective – fast – passive – gated - open or closed
Slide37Ion Channels-small aqueous holes • Properties – selective – fast – passive – gated - open or closed
Slide38CHANNELS- The pore in some channels can be opened or closed . - Opening/ closing of channels are controlled/ gated by a specific stimulus. - Example of a specific stimulus : i) Voltage; - VOLATGE - GATED CHANNEL ii) Ligand; - LIGAND -GATED CHANNELS iii) Specific stress; - STRESS – ACTIVATED CHANNELS
Slide39VOLTAGE - GATED CHANNELExample; Na+ voltage gated channels opens when the membrane potential depolarizes (i.e. becomes more positive). It has activation and inactivation gates.
Slide40LIGAND- GATED CHANNEL- Binding of a chemical ( ligand ) to a specific site on the receptor causes a change in membrane potential and causes it to allow a specific ion to pass through the channel in the membrane.
Slide41STRESS - ACTIVATED GATED ION CHANNEL- The channels open/close when a physical stress is applied to the channel protein - E.g. Auditory hair cells converts a physical stress to an electrical signal.
Slide42OK + O H H - O H H - O Selectivity Filter
Slide43OK + O H H - O H H - O Selectivity Filter
Slide44OK + O H H - O H H - O Selectivity Filter
Slide45OK + O H H - O H H - O Selectivity Filter
Slide46OK + O H H - O H H - O Selectivity Filter
Slide47OK + O H H - O H H - O Selectivity Filter O H H - O H H -
Slide48OK + O H H - O H H - O Selectivity Filter O H H - O H H -
Slide49ONa + O Selectivity Filter O H H O H H
Slide50OO Selectivity Filter Na + O H H O H H
Slide51OO Selectivity Filter Na + O H H O H H
Slide52زندگي ، خواب گراني است به ارزاني عمر
Slide533 Types of Gating
Slide54Active Transport• Used to move molecules against a gradient – REQUIRES ENERGY! • Two types 1 . Pumps 2 . Coupled Transport (co-transport)
Slide55Na+ /K + ATPase
Slide56Primary Active Transport:Pumps Products Figure 5-24: Mechanism of the Na + - K + -ATPase (75%)
Slide59•Cotransports • [Ion ] restored – using ATP Secondary Active Transport: Uses Kinetic Energy of [ion] Figure 5-25: Sodium-glucose symporter
Slide61EndocytosisExocytosis
Slide64(extracellular fluid)(cytoplasm) food particle particle enclosed in vesicle phagocytosis vesicle containing extracellular fluid cell pseudopod pinocytosis (a) (b) 1 3 3 2 1 3 2
Slide65Endocytosis and Exocytosis:VacuoleTransport Figure 5-28: Receptor-mediated endocytosis and exocytosis
Slide70•Cross two membranes – Apical – Basolatera • Absorption • Secretion Transepithelial and Transcytosis
Slide71Transepithelial andTranscytosis Figure 5-30: Transepithelial transport of glucose
Slide72Transepithelial and TranscytosisFigure 5-31: Transcytosis across the capillary endothelium