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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/8/3/2019 Sel Dan Membran
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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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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