MEMBRAN dan TRANSPORT.pdf
Transcript of MEMBRAN dan TRANSPORT.pdf
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MEMBRAN PLASMA dan TRANSPORT MELALUI MEMBRAN
Dr. Yahwardiah Siregar, PhD
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Malignant Hyperthermia
Malignant hyperthermia due to abnormal regulation of a calcium channel in muscle cells
Malignant hyperthermia is a severe, lifethreatening complication of anesthesia that may occur in persons with extreme hypersensitivity to halothane and similar agents used in general anesthesia.
Normally, a nerve impulse depolarizes the plasma membrane of a nerve ending at the nerve–muscle endplate (motor endplate), and the volt-gated calcium channel in the plasma membrane of the nerve ending is temporarily opened.
The massive influx of calcium into the cell (the extracellular Ca2 + concentration is about 1000 times higher than the intracellular) triggers the release of acetylcholine.
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Binding of the latter to the acetylcholine receptor of the muscle cell temporarily opens the receptor-controlled cation (Na+) channels.
This opens calcium channels located in the sarcoplasmic reticulum of the muscle cell. The resulting rapid increase in Ca2+ concentration in the cytosol causes the myofibrils in the muscle cell to contract.
The calcium channels in the sarcoplasmic reticulum are regulated by a receptor (ryanodin receptor)
Ryanodin (an alkaloid) binds to the calcium channel. The ryanodin receptor is a protein with four transmembrane domains
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Mutations in the ryanodin receptor lead to greatly increased sensitivity to halothane and other anesthetic agents, which cause muscle spasm, drastic elevation of temperature (hyperthermia), acidosis, and cardiac arrest.
Malignant hyperthermia is inherited as an autosomal dominant trait. One gene in man lies on chromosome 19 at 19q13.1 (MacLennan and Phillips, 1992).
Additional loci are on 7q, 17q, and 3q13.1 (Subrak et al., 1995).
The mutant haplotype of a given family can be determined by segregation analysis.
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Membran biologi mempunyai persamaan sifat:
1. Struktur lembaran tipis: 6 -10 nm
2.Terdiri dari lipid, protein dan sedikit karbo hidrat yang terikat pada lipid/protein.
3. Sebagai larutan dengan dua dimensi yg punya kerja timbal balik.
4. Struktur viscous tapi elastis, tertutup, asimetris dgn dua permukaan (bilayer).
MEMBRAN
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Membran plasma: melapisi seluruh fisik sel, memisahkan sel dari lingkungan Sekitar.
Menginternalisasi dan kompartementalisasi air dlm tubuh cairan intra dan ekstra sel
Bersifat selektif permeabel adanya
Channel, pompa ion / subsrat, reseptor spesifik
Sebagai sawar / barrier utk mempertahankan komposisi fisiologis ion / substrat di intra / ekstra sel
MEMBRAN PLASMA
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Memiliki reseptor utk molekul tertentu yg mengatur informasi antar sel dan sekitarnya.
Sel eukaryotik mempunyai membran dalam yg membentuk / membatasi organella spt : mitokondria, lisosom, ribosom, app.Golgi dll
Membran mitokondria sbg tempat proses pembentukan energi yg menghasilkan ATP (proses fosforilasi oksidatif)
MEMBRAN PLASMA
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Structure of cells
Plasma
Membrane
Endoplasmic
Retikulum
Golgi Apparatus
Lysosome
Mitochondrion
Cytoplasm
Nucleus
membrane
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UNSUR LIPID UTAMA MEMBRAN
1. Fosfolipid
2. Glikolipid
3. Kolesterol
Kolesterol :
- komponen utama dalam membran plasma, sedikit di badan golgi, mitokondria dan nukleus.
- Tersisip diantara fosfolipid, berperan dalam menentukan tingkat fluiditas membran.
Lipid membran mempunyai bagian hidrofob dan hidrofil sifat amfipatik.
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UNSUR PROTEIN MEMBRAN
Berdasar posisi pada membran prot. Integral dan peripher
1. Prot.Integral : globuler, amfipatik dengan dua ujung hidrofil yang dipisahkan regio hidrofob dalam lapisan bilayer lipid
2. Prot .Peripher : terikat lemah pada bagian hidrofil prot.Integral.
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TRANSPORT MATERI PADA MEMBRAN
1. Mekanisme pasif
Diffusi sederhana dan difasilitasi
Mengikuti gradien elektrokimia
Diffusi sederhana dipengaruhi oleh : gradien konsentrasi dan kelarutan solut
2. Mekanisme aktif
Transport aktif / pump
Menjauhi keseimbangan thermodinamika
Butuh energi (ATP) dan prot .Carrier
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TRANSPORT MELALUI MEMBRAN
Transport aktif primer : Na-K- ATP-ase , dll
Transport aktif sekunder : symport Na-glukosa, dll.
Sistem transport mengatur fungsional jumlah dan arah pergerakan molekul :
- Uniport
- Symport
- Antiport
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TRANSPORT oleh MEMBRAN
3. Endositosis dan eksositosis
Transport makromolekul (polisakarida, protein, polinukleotida dll )
Menggunakan pembentukan vesikel dari membran plasma
Endositosis untuk internalisasi
Eksositosis untuk eksternalisasi
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EKSOSITOSIS
Molekul yang dilepas digolongkan dalam:
1. Molekul yang terikat pada permukaan sel
2. Molekul yang menjadi bagian dari matriks ekstra sel.
3. Molekul yang diekstra sel menjadi sinyal bagi sel lain.
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