COMPILED BY :RAJA NOVI ARISKA

PENDIDIKAN BIOLOGI

THE FLUID MOSAIC MODEL OF THESTRUCTURE OF CELL MEMBRANE

S.J. Singer and Garth L. Nicolson

COMPILED BY :RAJA NOVI ARISKA

PENDIDIKAN BIOLOGI

Background

Cell membranes play an important role in cell, especiallyfor the exchange of substance inside and outside the cell.

The molecular structure and composition of cellmembrane need to be understand.

Tremendous and variable function, composition, anddetailed structure of protein affect cell membranesstructure.

Singer analysis that thermodynamics properties of cellmembranes is compiled by a mosaic structure ofalternating globular proteins and phospholipid bilayer.

The mosaic appears to be a fluid or dynamic one (twodimensional, viscous solution)

Cell membranes play an important role in cell, especiallyfor the exchange of substance inside and outside the cell.

The molecular structure and composition of cellmembrane need to be understand.

Tremendous and variable function, composition, anddetailed structure of protein affect cell membranesstructure.

Singer analysis that thermodynamics properties of cellmembranes is compiled by a mosaic structure ofalternating globular proteins and phospholipid bilayer.

The mosaic appears to be a fluid or dynamic one (twodimensional, viscous solution)

Cont.

Problem question:1. How the thermodynamics of macromolecular,

particularly membrane system, in aqueousenvironment?

2. What are the properties of protein and lipid onfunctional membranes?

3. How the structure of fluid mosaic model in detail?4. What are the recent and direct experimental evidence

for proposed models?5. How the fluid mosaic model suggest new ways of

thinking about membranes function and membranephenomena

Problem question:1. How the thermodynamics of macromolecular,

particularly membrane system, in aqueousenvironment?

2. What are the properties of protein and lipid onfunctional membranes?

3. How the structure of fluid mosaic model in detail?4. What are the recent and direct experimental evidence

for proposed models?5. How the fluid mosaic model suggest new ways of

thinking about membranes function and membranephenomena

Objectives :1. Review some thermodynamics of macromolecular,

particularly membrane system, in aqueousenvironment.

2. Discuss some properties of protein and lipid onfunctional membrane.

3. Describe the fluid mosaic model in detail.4. Analyze some recent and more direct experimental

evidence for proposed model.5. Show that the fluid mosaic model suggest new ways of

thinking about membranes function and membranephenomena.

Objectives :1. Review some thermodynamics of macromolecular,

particularly membrane system, in aqueousenvironment.

2. Discuss some properties of protein and lipid onfunctional membrane.

3. Describe the fluid mosaic model in detail.4. Analyze some recent and more direct experimental

evidence for proposed model.5. Show that the fluid mosaic model suggest new ways of

thinking about membranes function and membranephenomena.

DISCUSSION

1. Thermodynamics and Membrane Structure

The membrane systemscomposed of two kinds of non-covalent interactions,hydrophobic and hydrophilic.

Hydrophobic interaction: a set ofthermodynamic factors thatresponsible for sequesteringnonpolar groups away fromwater. (eq: water andhydrocarbons).

Hydrophobic as tail (water-fearing) it requires theexpenditure of 2.6 kilocalories offree energy to transfer a mole ofmethane from a non-polarmedium to water at 25°C.

The membrane systemscomposed of two kinds of non-covalent interactions,hydrophobic and hydrophilic.

Hydrophobic interaction: a set ofthermodynamic factors thatresponsible for sequesteringnonpolar groups away fromwater. (eq: water andhydrocarbons).

Hydrophobic as tail (water-fearing) it requires theexpenditure of 2.6 kilocalories offree energy to transfer a mole ofmethane from a non-polarmedium to water at 25°C.

Hydrophilic interactions is a set of thermodynamicfactors that are responsible for the preference of ionicand polar groups for an aqueous environment.

Hydrophilic as head (water-loving) requires energy totransfer a mole of zwitterionic glycine from water toacetone is about 6.0 kcal at 25°C, showing that ion pairsstrongly prefer to be in water.

Dipole-dipole interactions between ion pairs (such as inphatydilcholine) at the surface of the bilayer contributethe stabilization of bilayer structure.

Three major classes of membrane components: Proteins,lipids, and oligosaccharides.

Protein is the dominant (play important role indetermining the structure of membranes).

Hydrophilic interactions is a set of thermodynamicfactors that are responsible for the preference of ionicand polar groups for an aqueous environment.

Hydrophilic as head (water-loving) requires energy totransfer a mole of zwitterionic glycine from water toacetone is about 6.0 kcal at 25°C, showing that ion pairsstrongly prefer to be in water.

Dipole-dipole interactions between ion pairs (such as inphatydilcholine) at the surface of the bilayer contributethe stabilization of bilayer structure.

Three major classes of membrane components: Proteins,lipids, and oligosaccharides.

Protein is the dominant (play important role indetermining the structure of membranes).

2. Properties of Membrane ComponentPeripheral and integral proteins

a. Peripheral proteinCharacteristics:- Dissociate free of lipids- Require only mild treatments.- In the dissociated state they are

relatively soluble in neutralaqueous buffers.

- Peripheral protein is held to themebranes by weak noncovalentinteractions and not stronglyassociated with membrane lipid.

- Eq: cytochrome c ofmitochondrial membranes andprotein spectrin of erythrocytemembranes.

a. Peripheral proteinCharacteristics:- Dissociate free of lipids- Require only mild treatments.- In the dissociated state they are

relatively soluble in neutralaqueous buffers.

- Peripheral protein is held to themebranes by weak noncovalentinteractions and not stronglyassociated with membrane lipid.

- Eq: cytochrome c ofmitochondrial membranes andprotein spectrin of erythrocytemembranes.

b. Integral Protein- Major protein in cell

membranes (70%).- Require much more drastic

treatments to dissociatethem from membranes;

- in many instances, theyremain associated withlipids when isolated;

- if completely freed of lipids,they are usually highlyinsoluble or aggregated inneutral aqueous buffers.

- Assumed as the one type ofprotein arranged thestructure of cell membranes.

b. Integral Protein- Major protein in cell

membranes (70%).- Require much more drastic

treatments to dissociatethem from membranes;

- in many instances, theyremain associated withlipids when isolated;

- if completely freed of lipids,they are usually highlyinsoluble or aggregated inneutral aqueous buffers.

- Assumed as the one type ofprotein arranged thestructure of cell membranes.

Property of integral protein

1. Protein grossly heterogeneous with respect tomolecular weights.

2. The protein of variety intact membranes, on theaverage, show appreciable amounts of the α-helicalconformation (suggest that integral proteins in intactmembrane are largely globular in shape rather thanmonolayer.

1. Protein grossly heterogeneous with respect tomolecular weights.

2. The protein of variety intact membranes, on theaverage, show appreciable amounts of the α-helicalconformation (suggest that integral proteins in intactmembrane are largely globular in shape rather thanmonolayer.

3. Fluid Mosaic Modela. Mosaic structure of the proteins and lipids of membranes

Phospholipids are composedof amphipathic globularprotein.

The high polar region contactwith aqueous phase in intactmembran, consist of clusteredof ionic amino acid andcovalently boundoligosaccharides.

The non polar region isembedded inside themembrane.

The amino acid sequence inintegral protein able todetermine the amphipathicstructure.

Phospholipids are composedof amphipathic globularprotein.

The high polar region contactwith aqueous phase in intactmembran, consist of clusteredof ionic amino acid andcovalently boundoligosaccharides.

The non polar region isembedded inside themembrane.

The amino acid sequence inintegral protein able todetermine the amphipathicstructure.

Phospholipids with certain head groups can alter thesurface chemistry of a bilayer.

Lipid tails can also affect membrane properties;1. The bilayer can adopt a solid gel phase state at lower

temperatures.2. Become a fluid state at higher temperatures. The packing of lipids within the bilayer also affects

its mechanical properties, including its resistance tostretching and bending.

Phospholipids with certain head groups can alter thesurface chemistry of a bilayer.

Lipid tails can also affect membrane properties;1. The bilayer can adopt a solid gel phase state at lower

temperatures.2. Become a fluid state at higher temperatures. The packing of lipids within the bilayer also affects

its mechanical properties, including its resistance tostretching and bending.

Fluid Mosaic Model

At body temperature, the phospholipid bilayer is a liquid; The characteristic of globular protein is amphipathic. They are

structurally asymmetry, with one high polar end and one non polarend.

If the protein have the appropriate amino sequences and containamphiphatic structure, it can be included as integral protein.

The fluid-mosaic model, a working description of membrane structure,suggests that the protein molecules have a changing pattern (form amosaic) within the fluid phospholipid bilayer.

Our plasma membranes also contain a substantial number ofcholesterol molecules.

These molecules lend stability to the phospholipid bilayer and prevent adrastic decrease in fluidity at low temperatures.

At body temperature, the phospholipid bilayer is a liquid; The characteristic of globular protein is amphipathic. They are

structurally asymmetry, with one high polar end and one non polarend.

If the protein have the appropriate amino sequences and containamphiphatic structure, it can be included as integral protein.

The fluid-mosaic model, a working description of membrane structure,suggests that the protein molecules have a changing pattern (form amosaic) within the fluid phospholipid bilayer.

Our plasma membranes also contain a substantial number ofcholesterol molecules.

These molecules lend stability to the phospholipid bilayer and prevent adrastic decrease in fluidity at low temperatures.

4. Some evidence related to mosaic model

a. Evidence for proteins embedded in membranesThe results of recent freeze-etching experiments withmembranes strongly suggest that a substantial amountof protein is deeply embedded in many functionalmembranes.

b. Distribution of component in the plain of membraneIt is shown the distribution of membrane antigen over largearea surface membrane.The carbohydrate chains, specific to each cell, mark the cell asbelonging to a particular individual and account for suchcharacteristics as blood type or why a patient’s system sometimesrejects an organ transplant.

a. Evidence for proteins embedded in membranesThe results of recent freeze-etching experiments withmembranes strongly suggest that a substantial amountof protein is deeply embedded in many functionalmembranes.

b. Distribution of component in the plain of membraneIt is shown the distribution of membrane antigen over largearea surface membrane.The carbohydrate chains, specific to each cell, mark the cell asbelonging to a particular individual and account for suchcharacteristics as blood type or why a patient’s system sometimesrejects an organ transplant.

c. Protein is consist fluid state in intact internalmembrane

recent X-ray diffraction data of wet pellet receptor diskmembrane showed that :

(1) only a few order of reflection was observed related to thespacing of Rhodopsin in membranes. It means, nocrystalline aperiodic arrangement of particles is present inmembranes.

(2) X-ray diffraction maxima were consistent with idea thatparticles are in planar liquid-like state in intact membranes.

(3) Foreign protein absorption (Bovine serum albumin) to themembrane, alter x-ray spacing of rhodopsin becausealbumin weakly bind to membrane to rhodopsin non-rigidstructures causing aggregates in membrane, indicating theliquid-like state.

recent X-ray diffraction data of wet pellet receptor diskmembrane showed that :

(1) only a few order of reflection was observed related to thespacing of Rhodopsin in membranes. It means, nocrystalline aperiodic arrangement of particles is present inmembranes.

(2) X-ray diffraction maxima were consistent with idea thatparticles are in planar liquid-like state in intact membranes.

(3) Foreign protein absorption (Bovine serum albumin) to themembrane, alter x-ray spacing of rhodopsin becausealbumin weakly bind to membrane to rhodopsin non-rigidstructures causing aggregates in membrane, indicating theliquid-like state.

d. The asymmetry of membrane

Two surfaces of membranes are not identical instructure composition or function. This asymmetry iscome from the distribution of oligosaccharide on thetwo surface of membrane.

5. The Fluid Mosaic Model and Membrane Functions

The structure of cell membrane which viscous withamphipathic solution and lipid instantaneousthermodynamic equilibrium is lead to several function,related to transportation within and to the cell.

Physical and chemical perturbation can affect andchange the components of cell membrane, thus providenew thermodynamic interaction of altered components.

1. Malignant transformation of cells and the "exposure ofcryptic sites.

2. Cooperative phenomena in membranes.

The structure of cell membrane which viscous withamphipathic solution and lipid instantaneousthermodynamic equilibrium is lead to several function,related to transportation within and to the cell.

Physical and chemical perturbation can affect andchange the components of cell membrane, thus providenew thermodynamic interaction of altered components.

1. Malignant transformation of cells and the "exposure ofcryptic sites.

2. Cooperative phenomena in membranes.

CONCLUSION

1. The structure of phospholipid bilayer in aqueous environment isin amphipathic structure, which means, the lipid bilayer consist ofhydrophilic head and hydrophobic tails. The hydrophilic is consistof covalent bond (high polar) of phosphate and glycerol, while inhydropobic (non-polar) the tails is composed of fatty acid. Both ofthis structure is works cooperatively makes the structure of cellmembrane and its composition affect the fluidity of lipid bilayer.

2. There are two major proteins arrange its structure, peripheraland integral. The peripheral is located on the side of the bilayerand easier to breaks by mild treatments, while the integral isembedded in the bilayer. The integral is assumed as the mainprotein in the formation of lipid bilayer. The lipid itself has amajor role in the case of the fluidity of the cell membrane. Sincethe tail is consist of the fatty acid, the structure of tail effect thefluidity of bilayer.

1. The structure of phospholipid bilayer in aqueous environment isin amphipathic structure, which means, the lipid bilayer consist ofhydrophilic head and hydrophobic tails. The hydrophilic is consistof covalent bond (high polar) of phosphate and glycerol, while inhydropobic (non-polar) the tails is composed of fatty acid. Both ofthis structure is works cooperatively makes the structure of cellmembrane and its composition affect the fluidity of lipid bilayer.

2. There are two major proteins arrange its structure, peripheraland integral. The peripheral is located on the side of the bilayerand easier to breaks by mild treatments, while the integral isembedded in the bilayer. The integral is assumed as the mainprotein in the formation of lipid bilayer. The lipid itself has amajor role in the case of the fluidity of the cell membrane. Sincethe tail is consist of the fatty acid, the structure of tail effect thefluidity of bilayer.

3. The structure of fluid-mosaic at body temperature is aliquid;

4. There are four some recent evidence of cell membranestructures.a. protein are embedded in membraneb. the distribution of component in membranec. Protein is consist fluid state in intact internalmembraned. The asymmetry of membrane

5. The structure of cell membrane which viscous withamphipathic solution and lipid instantaneousthermodynamic equilibrium is lead to several function,related to transportation within and to the cell.

3. The structure of fluid-mosaic at body temperature is aliquid;

4. There are four some recent evidence of cell membranestructures.a. protein are embedded in membraneb. the distribution of component in membranec. Protein is consist fluid state in intact internalmembraned. The asymmetry of membrane

5. The structure of cell membrane which viscous withamphipathic solution and lipid instantaneousthermodynamic equilibrium is lead to several function,related to transportation within and to the cell.

REFERENCES

Alberts, Bruce et al. 2008. Molecular Biology of the Cell,Fifth Edition. Garland Science, Taylor and FrancisGroup. USA

Freeman.2003. Molecular Biology. (downloading from4shared.com on January, 2013)

Mader, Sylvia S. 2004. Understanding Human Anatomyand Physiology, Fifth Edition. Mc. Graw-Hill. USA

Singer, S.J and Garth L. Nicholson. 1972.The FluidMosaic Model of the Structure of CellMembranes.Published by: American Association for theAdvancement of Science.Vol. 175pp. 720-731.

Alberts, Bruce et al. 2008. Molecular Biology of the Cell,Fifth Edition. Garland Science, Taylor and FrancisGroup. USA

Freeman.2003. Molecular Biology. (downloading from4shared.com on January, 2013)

Mader, Sylvia S. 2004. Understanding Human Anatomyand Physiology, Fifth Edition. Mc. Graw-Hill. USA

Singer, S.J and Garth L. Nicholson. 1972.The FluidMosaic Model of the Structure of CellMembranes.Published by: American Association for theAdvancement of Science.Vol. 175pp. 720-731.