Sel Dan Membran

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    TINJAUAN PUSTAKA

    SEL Sel merupakan satuan terkecil organisme yang

    dibatasi dari lingkungannya oleh membran plasma(Syukri, 1999).

    Selain memisahkan diri dari lingkungan sekitarnya, seljuga perlu berhubungan dengan lingkungannya agartetap hidup (http://www.chem-is-try.org).

    http://www.chem-is-try.org/http://www.chem-is-try.org/http://www.chem-is-try.org/http://www.chem-is-try.org/http://www.chem-is-try.org/http://www.chem-is-try.org/
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    Gambar 1 Struktur Sel Tumbuhan

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    er e aan e ewan an eTumbuhan

    Sel Hewan Sel Tumbuhan

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    MEMBRAN SEL Senyawa utama penyusun membran adalah protein

    dan lipid (Lakitan, 1993).

    Komposisi lipid dan protein tergantung pada jenis danfungsi membran (http://bima.ipb.ac.id).

    Membran bersifat selektif permeabel(http://www.kompas.com).

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    Gambar 2 Struktur Membran Sel

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    FLUID because individual phospholipids and proteins canmove around freely within the layer, like its a liquid

    MOSAIC- because of the pattern produced by the scatteredprotein molecules when the membrane is viewed from

    above.

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    LIPID MEMBRAN Lipid membran terdiri dari fosfolipid dan kolesterol

    (Guyton, 1983).

    Fosfolipid tersusun atas bagian kepala yang bersifathidrofilik (polar) dan bagian ekor yang hidrofobik(non polar).

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    The Parts of Phospholipid Molecule

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    PROTEIN MEMBRAN Berdasarkan kekuatan ikatannya protein membran

    dibedakaan menjadi 2, yaitu: protein integral danprotein periferal (http://bima.ipb.ac.id).

    Protein berperan sebagai channel dan carrier sertapompa (Guyton, 1987).

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    Membrane-spanning alpha helices are the mostcommon structural motif in membrane proteins

    Structure Membrane Protein (1)

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    Structure Membran Protein (2)

    Each strand is hydrogen bonded to its neighbor inan antiparallel arrangement, forming a single betasheet

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    Small molecules and larger hydrophobicmolecules move through easily.e.g. O2, CO2, H2O

    Semipermeable Membrane

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    TRANSPORT MEMBRAN

    Membrane transport

    Small molecules

    Large molecules

    water

    nonpolar

    simple diffusion facilitated diffusion

    active transport

    cootransporters

    exocytosis pinocytosisendocytosis

    pumps

    passive transport

    ions

    permeases

    channels

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    Types of Transport Across

    Cell Membrane Passive Transport (Diffusion) :-Simple Diffusion: the diffusion of molecule that canpass through directly the membrane

    - Osmosis : the diffusion of water across aselectively permeable membrane

    - Facilitated Ion Diffusion: the diffusion of ion by

    gated in membrane Active Transport (Using ATP):the pumping of

    molecules or ions through a membrane againsttheir concentration gradient. Require energy

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    Osmosis

    Diffusion of wateracross a membrane

    Moves from HIGH

    water potential (lowsolute) to LOWwater potential

    (high solute)

    Diffusion across a membrane

    Semipermeablemembrane

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    Cell in Isotonic

    Solution

    CELL

    10% NaCL90% H2O

    10% NaCL90% H2O

    ENVIRONMENT

    NO NETMOVEMENT

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    Cell in Hypotonic

    Solution

    CELL

    10% NaCL90% H2O

    20% NaCL80% H2O

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    Cell in Hypertonic

    Solution

    CELL

    15% NaCL85% H2O

    5% NaCL95% H2O

    What is the direction of water movement?

    ENVIRONMENT

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    Osmosis in Red Blood Cells

    Isotonic Hypotonic Hypertonic

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    Facilitated Diffusion

    Some Carrierproteins do not

    extend through themembrane.

    They bond and dragmolecules through

    the lipid bilayer andrelease them on theopposite side.

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    Transmembrane Protein (1)

    Basic Transport Mechanism

    Uniporter : A uniporter is transmembranemembrane protein that is involved in facilitateddiffusion. They can be either a channel or a carrierprotein

    Symport-A symport is transmembrane protein thatis involved in movement of two or more differentmolecules or ions across a phospholipid membranesuch as the plasma membrane in the samedirection, and is therefore a type of cotransporter

    Antiporter-An antiporter (also called exchanger orcounter-transporter) is transmembrane proteinwhich is involved in secondary active transport oftwo or more different molecules or ions (i.e. solutes)across a phospholipid membrane such as theplasma membrane in opposite directions.

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    Mechanism Transport in

    Carrier protein

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    Transmembrane Protein (2)

    Carrier proteins, have moving parts to shiftspecific molecules across the membrane(Passive and Active transport)

    Channel proteins, from a narrow hydrophiliccore, allowing the passive movement of smallinorganic ions (only passive transport)

    Influenced by: electrochemical gradient

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    Carrier Transport

    The carriers involved behave like specializedmembrane-bound enzymes. Each type ofcarrier protein has one or more specific

    binding sites for its solute (substrate). When all these binding sites are occupied, the

    rate of transport is maximal

    Carrier Transport facilitate for passive and

    active transport. Ex: Valinomycin, protein carrier for pottassium

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    Hypothetical Model Carrier

    Protein Conformational

    change in a

    carrier proteincould mediatethe facilitateddiffusion of a

    solute

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    Passive

    Transport Other carrierproteins change

    shape to movematerials across

    the cell

    membranewithout ATP

    See animation 1

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    CoTransport

    Cotransport are similar to those in facilitated diffusionin that specific binding takes place and no ATP isexpended. It is different in that two substances mustbind at the same time before the transport takes place.

    Ex: Glucose and Na+ in the small intestine The highconcentration of glucose in the lumen provides theenergy for the transporter to move both Na+ andglucose out of the lumen and into the cell. Thistransport takes place even if the concentration of Na+

    in the lumen is less than in the cell. The Na+ thusmoves to a higher concentration, but only provided thefree energy required for this is less than that providedby the movement of glucose down its concentrationgradient.

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    Active Transport

    Requires energy or ATP

    Moves materials from Low to High

    concentration

    Against concentration gradient

    Examples: Pumping Na+ (sodium

    ions) out and K+ (potassium ions) in

    against strong concentrationgradients.

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    DIFUSI Menurut Poedjiadi (1994), dalam proses difusi zat

    dapat berpindah dari larutan berkonsentrasi tinggi kelarutan berkonsentrasi rendah hingga tercapai

    keadaan keseimbangan.

    Proses difusi dibedakan menjadi dua, yaitu: difusisederhana dan difusi terbantu(http://www.northland.cc.mn.us/biology).

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    TRANSPORT AKTIF Transpor aktif adalah perpindahan suatu zat yang

    bertentangan dengan gradien konsentrasi, denganmenggunakan sejumlah energi yang diperoleh dari

    dalam sel (Poedjiadi, 1994).

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    Gambar 2.4 Transport Aktif

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    POTENSIAL MEMBRAN Potensial membran timbul karena difusi ion dan

    transport aktif ion melewati membran (Guyton, 1974).

    Potensial membran lebih negatif di bagian dalamdibandingkan di bagian luar (Ganong, 1983).

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    Pembentukan ATP

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    Penggunaan ATP

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    Prinsip Kerja Pompa Na+-K+ dan Proses

    Pengangkutan AktifPompa Na+-K+

    Pengangkutan AktifATP

    ADP + PIdalam

    Membranluar

    lipoprotein K+ Na+

    lik t i