Presentation is loading. Please wait.

Presentation is loading. Please wait.

CELL MEMBRANE CELL MEMBRANE - is a 2-dimensional fluid mosaic of lipids and proteins and also is in constant motion. - It’s a thin, elastic structure,

Similar presentations

Presentation on theme: "CELL MEMBRANE CELL MEMBRANE - is a 2-dimensional fluid mosaic of lipids and proteins and also is in constant motion. - It’s a thin, elastic structure,"— Presentation transcript:





5 CELL MEMBRANE CELL 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.

6 CELL MEMBRANE -Lipid bilayer is made of 3 types of molecules ; 1. PHOSPHOLIPIDS 2. CHOLESTEROL 3. GLYCOLIPID.

7 Cholesterol

8 iii) 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).

9 Asymetrical Distribution of Lipids Modified from Figure 11-17, Page 355 from: Essential Cell Biology by Alberts et al. 1997, Garland Publishing Inc. New York, NY Extracellular Intracellular

10 Cholesterol can fill gaps between phospholipids Modified from Figure 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



13 MEMBRANE PROTEINS 1. 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

14 Membrane Proteins

15 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




19 PROPERTIES OF CELL MEMBRANES 1. 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


21 Phospholipids

22 Cholesterol


24 PROPERTIES 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.

25 PROPERTIES 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)


27 15.1 A pure phospholipid bilayer acts as a selectively permeable barrier Figure 15-1



30 Membrane Transport Simple Diffusion - 2 types of molecules 1. Small, nonpolar Oxygen 2. Small, polar, noncharged H 2 O (some - more later) Ethanol

31 Water Channels- The aquaporins H2OH2O H2OH2O HO HH H2OH2O Aquaporins Selectivity filter generated by hydrophobic residues that line the channel allowing only one molecule of water to pass at a time



34 Membrane Transport


36 Ion Channels -small aqueous holes Properties –selective –fast –passive –gated - open or closed

37 Ion Channels -small aqueous holes Properties –selective –fast –passive –gated - open or closed

38 CHANNELS -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

39 VOLTAGE - GATED CHANNEL Example; Na+ voltage gated channels opens when the membrane potential depolarizes (i.e. becomes more positive). It has activation and inactivation gates.

40 LIGAND- 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.

41 STRESS - 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.

42 O K+K+ O H H -- O H H -- O Selectivity Filter

43 O K+K+ O H H -- O H H -- O

44 O K+K+ O H H -- O H H -- O

45 O K+K+ O H H -- O H H -- O

46 O K+K+ O H H -- O H H -- O

47 O K+K+ O H H -- O H H -- O O H H -- O H H --

48 O K+K+ O H H -- O H H -- O O H H -- O H H --

49 O Na + O Selectivity Filter O H H O H H

50 O O Na + O H H O H H

51 O O Selectivity Filter Na + O H H O H H

52 زندگي ، خواب گراني است به ارزاني عمر

53 3 Types of Gating

54 Active Transport Used to move molecules against a gradient –REQUIRES ENERGY! Two types 1. Pumps 2. Coupled Transport (co-transport)

55 Na + /K + ATPase

56 Primary Active Transport: Pumps Products Figure 5-24: Mechanism of the Na + - K + -ATPase (75%)



59 Cotransports [Ion ] restored –using ATP Secondary Active Transport: Uses Kinetic Energy of [ion] Figure 5-25: Sodium-glucose symporter


61 Endocytosis Exocytosis



64 (extracellular fluid) (cytoplasm) food particle particle enclosed in vesicle phagocytosis vesicle containing extracellular fluid cell pseudopod pinocytosis (a) (b)

65 Endocytosis and Exocytosis: VacuoleTransport Figure 5-28: Receptor-mediated endocytosis and exocytosis





70 Cross two membranes –Apical –Basolatera Absorption Secretion Transepithelial and Transcytosis

71 Figure 5-30: Transepithelial transport of glucose

72 Transepithelial and Transcytosis Figure 5-31: Transcytosis across the capillary endothelium


Download ppt "CELL MEMBRANE CELL MEMBRANE - is a 2-dimensional fluid mosaic of lipids and proteins and also is in constant motion. - It’s a thin, elastic structure,"

Similar presentations

Ads by Google