2 MEMBRAN : membatasi lingk intrasel dg ekstrasel LOMemahami membran selpermeabilitas selImemahami lingkungan intraselMEMBRAN SELMEMBRAN : membatasi lingk intrasel dg ekstraselterdiri atas : LIPID dan PROTEIN,KH
3 MEMBRAN SEL * Tebal : 7,5 – 10 nm * 3 garis paralel - Electron dense layer :2 garis tebal, hitam lapisanpadat electron : 2,5 – 3 nm- Electron-lucent layer :1 lapisan diantaranya jernih :3,5– 4 nm
4 Komposisi membran sel 1. Lipid (40%) : - Phospholipid : * Phosphatidylcholine (lecithin)* Phosphatidylethanolamine (cephalin)- Sphingomyelin- CholesterolProteins (55%) : a. Integral proteins usually they are insolublein water solutions, are associated with lipids,this proteins may be attached tooligosaccharides forming glycoproteinsb. Peripheral proteins are soluble in aqueoussolutions, and are usually free of lipids3. Carbohydrates (5%) → oligosaccharide : - glycoproteins- glycolipids- glycocalyx
10 Protein Protein integral ; menembus dan tertanam dlm lapisan ganda, terikat pd bagian ekor nonpolara. Protein transmembran; membentuk saluran(pori-pori) → transport zat yg melewati membranb. peranannya:● Berikatan dng karbohidrat dpt membentuk sisireseptor untuk menerima pesan kimia dr sel lain :kelenjar endokrin● Sebagai pemberi tanda, atau antigen, yg menjadiidentitas jenis sel
11 2. Protein perifer : terikat pada permukaan membran, dapat dng mudah terlepas drmembran.Fungsi : - Protein ini mungkin terlibat dlmstruktur pendukung danperubahan bentuk membransaat pembelahan atau pergerakansel
12 Karbohidrat Karbohidrat juga berkaitan dng molekul lipid dan protein. dalam bentuk:* Glikolipid dan glikoprotein → mrpk sisipengenal permukaan untuk interaksi antar selmempertahankan sel-sel darah merah :- agar tetap terpisah- atau memungkinkan penggabungan sel-selyg sama untuk membentuk sebuah jaringan.
13 Fungsi membran sel: Protective function: The cell membrane protects the cytoplasmand the organelles of the cytoplasm.As a semipermeable membrane:The cell membrane permits only someselective substances to pass through itand acts as a barrier for other substances.Absorptive function:The nutrients are absorbed into the cellthrough the cell membrane.
14 Excretory function:The metabolites and other waste productsfrom the cell are excreted out through thecell membrane.Exchange of gases:Oxygen enters the cell from the blood andcarbon dioxide leaves the cell and entersthe blood trough the cell membrane.Maintenance of shape and size of the cell:The cell membrane is responsible for themaintenance of shape and size of the cell.
19 Pergerakan materi menembus membran selPrinsip dasar : * TRANSPORT PASIF* TRANSPORT AKTIF* Mekanisme transport pasif :● difusi bebas● osmosis● difusi terfasilitasi● filtrasi* Mekanisme transport aktif : - memerlukan energi,- enzim
20 Mekanisme transport aktif 1. Transport aktif diperantarai carrierCarrier : protein integral yg disebut pompa→ pompa ion natrium/kalium yg aktifdlm sel hidup.→ Pompa kalsium : - kontraksi otot2. Transport massa berukuran besar : vesikel(vakuola) → * Fagositosis* Pinositosis* Endositosis* Eksositosis
21 Transport protein, mekanisme pembawa, dan poros tetap Transport molekul-molekul berbeda melewati membran memperlihatkan spesifitas tinggiPermeabilitas molekul berkaitan dengan susuna kimianya.Macam selektifitas ini berkaitan dengan transport protein → carrier / pembawaAda 2 hipotesis :1. mekanisme carrier2. mekanisme poros tetap
23 Difusi Water* Gases - CO2 - N2 - O2 Small uncharged polar molecules - ethanol- urea*Hydrophobic molecules- steroid hormones
24 Large uncharged polar molecules - glucose Charged polar molecules Must be transported !Ions- K+, Na+, Mg2+, Ca2+, Cl-, HCO3-,HPO42-Large uncharged polar molecules- glucoseCharged polar molecules- amino acids- ATP
25 Hypothetical diagram of simple diffusion through the cell membrane Hypothetical diagram of simple diffusion through the cell membrane. A = Diffusion through lipid layer. B = Diffusion through ungated channel. C - Diffusion through gated channel.
26 Transport of Small Molecules selectively permeable to small molecules.melalui phospholipid bilayer, membran plasma membentuk barrier yang menghalangi pertukaran molekul antarastiplasma dg lingk eksternal selSpecific transport proteins (carrier proteins and channel proteins) then mediate the selective passage of small molecules across the membrane, allowing the cell to control the composition of its cytoplasm.
27 Mobility of phospholipids in a membrane Individual phospholipids can rotate and move laterally within a bilayer.
28 Permeability of phospholipid bilayers Small uncharged molecules can diffuse freely through a phospholipid bilayer. However, the bilayer is impermeable to larger polar molecules (such as glucose and amino acids) and to ions.
29 Permeability of phospholipid bilayers : Gases, hydrophobic molecules, and small polar can diffuse through phospholipid bilayers. Larger polar molecules and charged molecules cannot
30 Hypothetical diagram of facilitated diffusion from higher concentration (ECF) to lower concentration (ICF). through the cell membrane. Stage 1. Glucose binds with carrier protein. Stage 2. Conformational change occurs in the carrier protein and glucose is released into ICF.
31 Ion channels Conduct ions 10 ions/sec Recognize & select specific ions 8Conduct ions 10 ions/secRecognize & select specific ionsOpen and close in response to specific signals
32 Channel and carrier proteins (A) Channel proteins form open pores through which molecules of the appropriate size (e.g., ions) can cross the membrane. (B) Carrier proteins selectively bind the small molecule to be transported and then undergo a conformational change to release the molecule on the other side of the membrane.
33 Model of active transport Energy derived from the hydrolysis of ATP is used to transport H+ against the electrochemical gradient (from low to high H+ concentration) Binding of H+ is accompanied by phosphorylation of the carrier protein, which induces a conformational change that drives H+ transport against the electrochemical gradient Release of H+ and hydrolysis of the bound phosphate group then restore the carrier to its original conformation.
34 Transporter Uniporter - The facilitated diffusion of glucose is an example of uniport, the transportof only a single molecule.Symporter - The coordinate uptake of glucoseand Na+ is an example of symport,the transport of two molecules in thesame direction.Antiporter - Active transport can also take place byantiport, in which two molecules aretransported in opposite directions.
35 Model of an ion channelIn the closed conformation, the flow of ions is blocked by a gate.Opening of the gate allows ions to flow rapidly through the channel. The channel contains a narrow pore that restricts passage to ions of the appropriate size and charge.
36 Examples of uniport: Model for the facilitated diffusion of glucose The glucose transporter alternates between two conformations in which a glucose-binding site is alternately exposed on the outside and the inside of the cell.In the first conformation shown (A), glucose binds to a site exposed on the outside of the plasma membrane.The transporter then undergoes a conformational change such that the glucose-binding site faces the inside of the cell and glucose is released into the cytosol (B).The transporter then returns to its original conformation (C).
37 Examples of symport : Glucose transport by intestinal epithelial cellsThe glucose transporter alternates between two conformations in which a glucose-binding site is alternately exposed on the outside and the inside of the cell.In the first conformation shown (A), glucose binds to a site exposed on the outside of the plasma membrane.The transporter then undergoes a conformational change such that the glucose-binding site faces the inside of the cell and glucose is released into the cytosol (B).The transporter then returns to its original conformation (C).
38 Examples of antiportCa2+ and H+ are exported from cells by antiporters, which couple to their export to the energetically favorable import of Na+.
39 Summary Membrane Structure Membrane models have evolved to fit new data: science as a prossesA membrane is a fluid mosaic of lipids, protein, and carbohydratesOsmosis in the passive transport of waterCell survival depends on balancing water uptake and lossSpecific protein facilitate the passive transport of selective solutes
40 Summary Traffic Across Membranes Active transport is the pumping of solute against their gradiensSome of ion pumps generate voltage across membranesIn cotransport, a membrane protein couples the transport of one solute to anotherExocytosis and endocytosis transport large molecules
42 Overview of lipids and proteins. ■ The cell membrane is mainly composedof lipids and proteins.■ Its frame work consists of a double layer ofphospholipids.■ There are two major types of proteins : tightly coiled, rod –shaped, fibrous proteins and the more compact, globular – shaped integral proteins and peripheral proteins.
43 These are the different types of molecules of the cell membrane. Fibrous proteinPhospholipidExamples of globular – shaped proteinsH2O MoleculeNa+GlycoproteinPore proteinChannel proteinGlycoprotein Pore protein Channel protein
44 ■ Two layer of phospholipids molecules self – assemble so that their water soluble (hydrophilic) heads formthe surface and interior of the membrane, and thewater insoluble (hydrophobic) tails face each other.Hydrophobic tailsHydrophilic heads
45 ■ The fibrous proteins may span the entire membrane and serve as receptors for the cell
46 ■ One type of globular protein form “pores” to allow lipid insoluble water molecules to pass through.H2O Molecule
47 ■ Other integral proteins serve as channel proteins and selectively transport ions for the cell.H2O MoleculeNa+
48 ■ Globular proteins, which are peripheral (associated with the surface of the cell), may be enzymes or glycoproteins (proteinswith carbohydrate associations that identify the cell.H2O MoleculeNa+
49 ■ Cholesterol molecules are embedded in animal cell. Membranes but not in plant cell membranes, they help make themembrane (along with the phospholipids) impermeable to water-soluble substances. Cholesterol also stabilized themembrane.H2O MoleculeNa+
50 ● EXOCYTOSIS ● FILTRATION ● OSMOSIS ● ENDOCYTOSIS SPECIAL CATEGORIES OF TRANSPORT● ENDOCYTOSIS● EXOCYTOSIS● FILTRATION● OSMOSIS
54 to a dilute solution through a cell membrane. Osmosisis the movement of water from a concentrated solutionto a dilute solution through a cell membrane.
55 PermeablePermeable is having pores or openings that permit liquids or gases to pass through, or that something is capable of being permeated.
56 VacuoleA vacuole is found in both plant and animal cells, but in the plant cells there are fewer of them yet they are larger and in the animal cells the are small. They have fluid filled sacs and store food, water and waste (plants need to store large amounts of food). Vacuoles have membrane-bound sacs for storage, digestion and waste removal. They also contain water solutions.