Download pdf - Sel Dan Membran

8/3/2019 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).


8/38Gambar 3 Fosfolipid


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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