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    Cell Biology Resume

    THE FLUID

    THE ST

    S.J. Singe

    R

    PE

    PASCA SARJAN

    MOSAIC MODEL O

    UCTURE OF CELLEMBRANE

    r and Garth L. Nicolson

    C

    O

    M

    P

    I

    L

    E

    D

    By :

    AJA NOVI ARISKA

    8136173013

    DIDIKAN BIOLOGI

    UNIVERSITAS NEGERI MEDAN

    2013/2014

    F

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    I. Title : THE FLUID MOSAIC MODEL OF THE STRUCTURE

    OF CELL MEMBRANE

    II. Objectives :

    1. Review some thermodynamics of macromolecular, particularly membrane

    system, in aqueous environment.

    2. Discuss some properties of protein and lipid on functional 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 membrane phenomena.

    III. Introduction

    The article of Singer and Nicolson is talked about the fluid mosaic model of

    cell membrane structure. Since the cell membranes play an important role in cell,

    the molecular of its structure need to be understand.

    Singer examined in considerable detail several models of the gross

    structural organization of membranes, in terms of the thermodynamics of

    macromolecular systems and in the light of the then available experimentalevidence. From his analysis, it was concluded that a mosaic structure of

    alternating globular proteins and phospholipid-bilayer was the only membrane

    model among those analyzed that was simultaneously consistent with

    thermodynamic restrictions and with all the experimental data available.

    This article present and discuss a fluid mosaic model of membrane

    structure, its components properties, and propose that it is applicable to most

    biological membranes, such as plasmalemmal and intracellular membranes,

    including the membranes of different cell organelles, such as mitochondria and

    chloroplasts. These membranes are henceforth referred to as functional

    membranes.

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    IV. Discussion

    a. Thermodynamics a

    The fluid mosaic mo

    version. It indicates that the

    covalent interactions are mo

    amphipathic.

    Hydrophobic as tail

    thermodynamic factors that a

    non-polar groups away fr

    hydrocarbons and water. T

    kilocalories of free energy to

    to water at 25C.

    Hydrophilic as head

    thermodynamic factors that

    groups for an aqueous rather

    required to transfer a mole o

    6.0 kcal at 25C, showing t

    non-polar medium.

    The hydrophilic ar

    wateryenvironment. The hy

    When phospholipids are pla

    because of the chemical prop

    Figure 1. pho

    d Membrane Structure

    el has evolved by a series of stages from ea

    membrane systems composed of two kinds of

    t important, hydrophobic and hydrophilic, know

    (water-fearing) interactions means a set

    re responsible for the sequestering of hydrophob

    m water, as, for example, the immiscibilit

    o be specific, it requires the expenditure of

    transfer a mole of methane from a non-polar me

    (water-loving) interactions is meant a se

    re responsible for the preference of ionic and

    than a non-polar environment. Thus, the free en

    f zwitterionic glycine from water to acetone is a

    at ion pairs strongly prefer to be in water than

    face outward and likely to encounte

    rophobic are face inward, where there is no w

    ed in water, they naturally form a spherical bil

    erties of the heads and the tails (Mader.2004).

    pholipid molecule (source: Freeman, 2003)

    rlier

    non-

    n as

    of

    ic or

    of

    2.6

    ium

    of

    olar

    ergy

    bout

    in a

    r a

    ater.

    ayer

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    There are other non-

    electrostatic interactions, w

    structure. However, with r

    concerned, these are very lik

    and hydrophilic interactions.

    The non-polar fatty

    together away from conta

    interactions. Furthermore, th

    with the aqueous phase at th

    hydrophilic interactions. In

    phosphatidylcholine, dipole-

    the bilayer may also contribuThe tail in cell mem

    double bound in one tail. It c

    affect the packing and fluidit

    Figure 2. Mo

    The double cis-bond

    making lipid bilayer hard to

    of unsaturated lipid is more s

    lipid .

    ovalent interactions, such as hydrogen bonding

    hich also contribute to determine macromole

    spect to gross structure, with which we are

    ly of secondary magnitude compared to hydroph

    acid chains of the phospholipids are sequest

    ct with water, thereby maximizing hydroph

    ionic and zwitter-ionic groups are in direct co

    exterior surfaces of the bilayer, thereby maximi

    the case of zwitterionic phospholipids suc

    ipole interactions between ion pairs at the surfa

    te to the stabilization of the, bilayer structure.brane have variable in length. It caused by the

    ause small kink in the structure of cell membrane

    of cell membrane. (Alberts, 2008)

    lecular structure of amphipathic structure

    akes more difficult to pack the chains together,

    reeze. In addition, because of the hydrocarbon ch

    pread apart, it has thinner structure than the satur

    and

    ular

    now

    obic

    ered

    obic

    tact

    zing

    as

    e of

    cis-

    and

    thus

    ains

    ated

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    b. Some Properties

    Peripheral and integr

    Peripheral protein has

    (i) They require onl

    strength of the

    dissociate them m

    (ii) They dissociate fr

    (iii) In the dissociate

    buffers is held to

    (perhaps mainly el

    with membrane lip

    F

    On the other hand, t

    namely:

    (i) They require m

    detergents, bile

    dissociate them f

    (ii) In many instance

    (iii) If completely fr

    aggregated in neu

    f Membrane Components

    l proteins.

    several characteristics:

    mild treatments, such as an increase in the i

    edium or the addition of a chelating agen

    lecularly intact from the membrane;

    ee of lipids; and

    state they are relatively soluble in neutral aqu

    the membrane only by rather weak non-cov

    ctrostatic) interactions and is not strongly associ

    id.

    igure 3. Protein of lipid bilayer

    e integral proteins also have several characteri

    ch more drastic treatments, with reagents suc

    acids, protein denaturants, or organic solvent

    om membranes;

    , they remain associated with lipids when isolate

    eed of lipids, they are usually highly insolubl

    tral aqueous buffers.

    onic

    , to

    ous

    lent

    ated

    tics,

    h as

    , to

    d;

    e or

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    Figure

    Integral proteins gros

    also suggested that the integspread in a monolayer.

    Lipid-anchored me

    lipid molecules. The hydrop

    in one leaflet of the membr

    polypeptide chain itself does

    Figure 3. pr

    . Type of protein based on its location

    sly heterogeneous and vary in molecular weig

    ral proteins are largely globular in shape rather

    brane proteins are bound covalently to one or

    obic carbon chain of the attached lipid is embe

    ane and anchors the protein to the membrane.

    not enter the phospholipid bilayer.

    perties of protein in cell membrane

    t. It

    than

    ore

    ded

    The

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    c. Fluid Mosaic Model

    The characteristic of globular protein is same as the lipid bilayer, namely

    amphipathic. They are structurally asymmetry, with one high polar end and one

    non polar end. The highly polar region is one in which the ionic amino acid

    residues and any covalently bound saccharide residues are clustered, and which is

    in contact with the aqueous phase in the intact membrane; the nonpolar region is

    devoid of ionic and saccharide residues, contains many of the nonpolar residues,

    and is embedded in the hydrophobic interior of the membrane.

    If the protein have the appropriate amino sequences and contain

    amphiphatic structure, it can be included as integral protein. An integral protein

    molecule with the appropriate size and structure, or a suitable aggregate of

    integral proteins (below) may transverse the entire membrane that is, they haveregions in contact with the aqueous solvent on both sides of the membrane.

    The reason why some proteins are membrane bound and others are freely

    soluble in the cytoplasm because the amino acid sequence of the particular protein

    allows it to adopt an amphipathic structure or, on the contrary, to adopt a structure

    in which the distribution of ionic groups is nearly spherically symmetrical, in the

    lowest free energy state of the system.

    If the ionic distribution on the protein surface were symmetrical, the protein

    would be capable of interacting strongly with water all over its exterior surface,that is, it would be a monodisperse soluble protein.

    At body temperature, the phospholipid bilayer is a liquid; it has the

    consistency of olive oil, and the proteins are able to change their positions by

    moving laterally. The fluid-mosaic model, a working description of membrane

    structure, suggests that the protein molecules have a changing pattern (form a

    mosaic) within the fluid phospholipid bilayer. Our plasma membranes also

    contain a substantial number of cholesterol molecules. These molecules lend

    stability to the phospholipid bilayer and prevent a drastic decrease in fluidity atlow temperatures.

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    Figu

    Short chains of sugarand lipid molecules (called

    carbohydrate chains, specifi

    particular individual and acc

    patients system sometimes r

    Some glycoproteins h

    a receptor for a chemical me

    proteins form channels thro

    others are carriers involved(Fremann.2003)

    e 5. phospholipid bilayer structure

    s are attached to the outer surfaces of some pr glycoproteins and glycolipids, respectively). T

    c to each cell, mark the cell as belonging

    ount for such characteristics as blood type or w

    jects an organ transplant.

    ave a special configuration that allows them to a

    ssenger such as a hormone. Some plasma memb

    gh which certain substances can enter cells,

    in the passage of molecules through the memb

    teinhese

    o a

    hy a

    t as

    rane

    hile

    rane

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    Figure 6. Dynamic of Phospholipid

    Matrix of the mosaic, lipid or protein?

    It is not well determine which components are arrange the matrix of the

    mosaic. This question must be answered when the third dimension of the mosaicstructure is specified.

    If the membrane proteins formed the matrix of the mosaic, defined by

    specific contacts between the molecules of different integral proteins, protein A

    might be distributed in a highly ordered, two dimensional array on the surface. On

    the other hand, if lipid formed the matrix of the mosaic, there would be no long-

    range interactions intrinsic to the membrane influencing the distribution of A

    molecules, and they should there-fore be distributed in an aperiodic random

    arrangement on the membrane surface.If a membrane consisted of integral proteins dispersed in a fluid lipid

    matrix, the membrane would in effect be a two-dimensional liquid-like solution of

    mon-omeric or aggregated integral proteins (or lipoproteins) dissolved in the lipid

    bilayer. The mosaic structure would be a dynamic rather than a static one. The

    integral proteins would be expected to undergo translational diffusion within the

    membrane, at rates determined in part by the effective viscosity of the lipid, unless

    they were tied down by some specific interactions intrinsic or extrinsic to the

    membrane. However, because of their amphipathic structures, the integral proteinswould maintain their molecular orientation and their degree of intercalation in the

    membrane while undergoing translational diffusion in the plane of the membrane.

    In contrast, if the matrix of the mosaic were constituted of integral

    proteins, the long-range structure of the membrane would be essentially static.

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    Large energies of activation would be required for a protein component to diffuse

    in the plane of the membrane from one region to a distant one because of the

    many non-covalent bonds between the proteins that would have to be

    simultaneously broken for exchange to take place. Therefore, a mosaic membrane

    with a protein matrix should make for a relatively rigid structure with essentially

    no translational diffusion of its protein components within the membrane.

    d. Some evidence related to mosaic model

    1. Evidence for proteins embedded in membranes

    The results of recent freeze-etching experiments with membranes strongly

    suggest that a substantial amount of protein is deeply embedded in many

    functional membranes.Methods : a frozen specimen is fractured with a microtome knife; some of the

    frozen water is sub-limed (etched) from the fractured surface if desired; the

    surface is then shadow cast with metal, and the surface replica is examined in the

    electron microscope. A characteristic feature of the exposed surface of most

    functional membranes examined by this technique, including plasmalemmal,

    vacuolar, nu-clear, chloroplast, mitochondrial, and bacterial membranes is a

    mosaic-like structure consisting of a smooth matrix interrupted by a large number

    of particles. These particles have a fairly characteristic uniform size for aparticular membrane, for example, about 85 diameter for erythrocyte

    membranes. Such surfaces result from the cleavage of a membrane along its

    interior hydrophobic face.

    2. Distribution of component in the plain of membrane.

    The distribution of component in plain of membrane can be visualized by

    using electron microscopy. It is shown the distribution of membrane antigen over

    large area surface membrane.

    Thus, analyzing the distribution of Rho(D) antigen of human erythrocytemembrane cell. The O Rh positive react with saturating amount 125I labeled

    purified human antibody against Rho(D)/anti Rho(D). The cell is lysed at air-

    water interface causing the cell membrane flattened. The cell then picked up on

    electron microscope grid. Staining method is then occupied using indirect stain

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    (ferritin conjugated goat spe

    whenever anti Rho(D)/ boun

    goat attached. ( globulin

    This indicates that there rel

    radius 300 . The cluster/un

    human and an Rho(D) mole

    ferritin bound to anti Rho

    molecules bound to a single

    conclude that Rho(D)/ anti

    distributed randomly in two

    3. Protein is consist

    There present tightl

    rhodopsin). Earlier studies

    particles distribution. But remembrane showed that (1) o

    the spacing of Rhodopsin

    arrangement of particles is

    were consistent with idea t

    cific for human globulins). The results show

    d to Rho antigen on surface membrane, the fer

    uman antibody became antigen for goat antib

    ation between clusters of 2-8 ferritin molecule

    it area is in balance between the total of125I la

    ules bound/unit area. Or in other word every cl

    D) and the cluster is the total of goat anti

    human Y globulin molecules (one cluster),a we

    gen which possess integral protein properties

    imensional array.

    luid state in intact internal membrane

    packages ordered array particles (the particl

    howed that there was a long range order of t

    ent X-ray diffraction data of wet pellet receptornly a few order of reflection was observed relat

    in membranes. It means, no crystalline aperi

    resent in membranes. (2) X-ray diffraction ma

    at particles are in planar liquid-like state in i

    that

    ritin

    dy).

    s on

    eled

    ster

    ody

    can

    are

    s in

    hese

    diskd to

    odic

    ima

    tact

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    membranes. (3) Foreign protein absorption (Bovine serum albumin) to the

    membrane, alter x-ray spacing of rhodopsin because albumin weakly bind to

    membrane to rhodopsin non-rigid structures causing aggregates in membrane,

    indicating the liquid-like state.

    4. The asymmetry of membrane

    Two surfaces of membranes are not identical in structure composition or

    function. This asymmetry is come from the distribution of oligosaccharide on

    the two surface of membrane. Technique : There exist plant proteins, called

    lectins or plant agglutinins, which bind to specific sugar residues, and, as a

    result, can cause the agglutination of cells bearing the sugar residues on their

    surfaces. The authors have been able to visualize the distribution of

    oligosaccharides on membranes in the electron microscope.

    e. The Fluid Mosaic Model and membrane functions

    The structure of cell membrane which viscous with amphipathic solution

    and lipid instantaneous thermodynamic equilibrium is lead to several functions

    related to transportation within and to the cell. Physical and chemical perturbation

    can affect and change the components of cell membrane, thus provide new

    thermodynamic interaction of altered components.

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

    Malignant trans-formation is closely correlated with a greatly increased

    capacity for the trans-formed cells to be agglutinated by several saccharides

    binding plant agglutinins. Mild treatment of normal cells with proteolytic enzymes

    can render malignant also more readily agglutinable by these protein agglutinins.

    Burger has suggested, therefore, that the agglutinin-binding sites are pres-ent on

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    the membrane surfaces of nor-mal cells but are "cryptic" and that proteolytic

    digestion of normal cells or the processes of malignant transformation "exposes"

    these cryptic sites on the membrane surface. In some cases, quantitative binding

    studies have indeed indicated that no significant change in the numbers of

    agglutinin-binding sites on the membrane accompanies either mild proteolysis of

    normal cells or malignant transformation.

    2. Cooperative phenomena in membrane

    Trans effects refer to cooperative (allosteric) changes that have been

    postulated to operate at some localized region on the membrane surface, to

    transmit an effect from one side of the membrane to the other. For example, fan

    integral protein may exist in the membrane as an aggregate of two (or more)

    subunits, one of which is exposed to the aqueous solution at the outer surface ofthe membrane, and the other is exposed to the cytoplasm at the inner surface. The

    specific binding of a drug or hormone molecule to the active site of the outward-

    oriented subunit may induce a conformational rearrangement within the

    aggregate, and thereby change some functional property of the aggregate or of its

    inward-oriented subunit. By cis effects, on the other hand, we refer to cooperative

    changes that may be produced over the entire membrane, or at least large areas of

    it, as a consequence of some event or events occurring at only one or a few

    localized points on the membrane surface. For example, the killing effects ofcertain bacteriocins on bacteria, the lysis of the cortical granules of egg cells upon

    fertilization of eggs by sperm, and the interaction of growth hormone with

    erythrocyte membranes are cases which may involve transmission and

    amplification of local-ized events over the entire surface of a membrane.

    V. Conclusion

    1. The structure of phospholipid bilayer in aqueous environment is in

    amphipathic structure, which means, the lipid bilayer consist ofhydrophilic head and hydrophobic tails. The hydrophilic is consist of

    covalent bond (high polar) of phosphate and glycerol, while in hydropobic

    (non-polar) the tails is composed of fatty acid. Both of this structure is

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    works cooperatively makes the structure for its proper function and its

    composition affect the fluidity of lipid bilayer.

    2. In lipid bilayer, there are two major proteins arrange its structure,

    peripheral and integral. The peripheral is located on the side of the bilayer

    and easier to breaks by mild treatments, while the integral is embedded in

    the bilayer. The integral is assumed as the main protein in the formation of

    lipid bilayer. The lipid itself has a major role in the case of the fluidity of

    the cell membrane. Since the tail is consist of the fatty acid, the structure

    of tail effect the fluidity of bilayer, especially the unsaturated, kinky

    structure.

    3. The structure offluid-mosaic at body temperature is a liquid; a working

    description of membrane structure, suggests that the protein moleculeshave a changing pattern (form a mosaic) within the fluid phospholipid

    bilayer. Our plasma membranes also contain a substantial number of

    cholesterol molecules. These molecules lend stability to the phospholipid

    bilayer and prevent a drastic decrease in fluidity at low temperatures.

    4. There are four some recent evidence of cell membrane structures.

    a. protein are embedded in membrane

    b. the distribution of component in membrane

    c. Protein is consist fluid state in intact internal membraned. The asymmetry of membrane

    5. The structure of cell membrane which viscous with amphipathic solution

    and lipid instantaneous thermodynamic equilibrium is lead to several

    function, related to transportation within and to the cell. Physical and

    chemical perturbation can affect and change the components of cell

    membrane, thus provide new thermodynamic interaction of altered

    components.

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    REFERENCES

    Alberts, Bruce et al. 2008. Molecular Biology of the Cell, Fifth Edition. GarlandScience, Taylor and Francis Group. USA

    Freeman.2003.Molecular Biology. (downloading from 4shared.com on January,2013)

    Mader, Sylvia S. 2004. Understanding Human Anatomy and Physiology, FifthEdition. Mc. Graw-Hill. USA

    Singer, S.J and Garth L. Nicholson. 1972.The Fluid Mosaic Model of the

    Structure of Cell Membranes.Published by: American Association for the

    Advancement of Science.Vol. 175pp. 720-731.