1 Membranes Chapter 1

2 Phospholipid Bilayer Phospholipid 2 fatty-acid chains Glycerol + Phosphate + nitrogenous compound One end strongly non-polar Other end strongly polar Polar head Hydrophilic Nonpolar tails Hydrophobic

3 Cell Membrane Structure Davson-Danielli Model (1935)— phopholipid bilayer sandwiched between 2 protein layers. Singer-Nicolson, Fluid Mosaic Model (1972)—Membrane proteins embedded in phospholipid bilayer. Proteins free to move in the lipid bilayer. Cell membrane is selectively permeable

4 Components of Cell Membrane Eukaryotic cells have many membranes. All share similar structure 4 components: Phospholipid bilayer— All other components embedded in bilayer. Barrier to water- soluble molecules Transmembrane proteins— Span width of bilayer. Involved in transport. Can move within bilayer Interior protein network— Membranes supported by intracellular proteins. Other proteins allow for movement of transmembrane proteins within bilayer. Cell surface markers— Sections of cell membrane have different types of glycolipids and glycoproteins. Act as cell identity markers.

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6 Types of Membrane Proteins Transporters- Involved in the movement of substances. Enzymes- Allow chemical reactions on the interior of membrane Cell surface receptors- Detect chemical messages Cell surface identity markers- different cell types have unique markers Cell adhesion proteins- cause cells to stick to one another Attachments to cytoskeleton- proteins attach to cytoskeleton

7 Membrane Protein Structure Anchoring proteins to the bilayer- Modified lipids link to membrane phospholipid and bond directly to protein. Protein tethered to cell membrane Transmembrane proteins- nonpolar region of protein in bilayer polar regions extend outward Different types – Single-pass anchors- pass through bilayer only once  Ex hormone receptors – Multiple-pass channels and carriers- multiple alpha helix sections pass through membrane (move ions and water soluble molecules) – Pores- beta sheet sections of protein form large opening that allow water and other material to move through membrane

8 Movement of materials across cell membrane Passive Transport —Does NOT require energy Diffusion Facilitated Diffusion Osmosis Active Transport —Requires the expenditure of energy Sodium-Potassium Pump Coupled Transport Other means Endocytosis—Phagocytosis and Pinocytosis Receptor-mediated endocytosis Exocytosis

9 Molecules and Ions move about constantly and randomly Diffusion – Net movement from areas of high concentration to areas of low concentration. Equilibrium Passive Transport

10 Cell Membrane Is Selectively Permeable Many molecules needed by cells are polar Polar molecules cannot cross non-polar Phospholipid barrier Polar molecules diffuse through channel proteins Different types of channels assist specific molecules Ions diffuse through Ion Channels Cations and Anions cannot move through phospholipid layer Interior of channel proteins is polar

11 Facilitated Diffusion Carrier Proteins transport ions and other solutes (ex. glucose and amino acids) across membrane down concentration gradient Facilitate movement by physically binding molecules on one side of membrane then releasing them on the other (configuration change) Characteristics of Facilitated diffusion Specific- each carrier type transports specific molecules Saturates- if all carriers in use, Increase in gradient does not Increase rate of transport

12 Osmosis Diffusion of water across a selectively permeable membrane Cytoplasm of a cell is an Aqueous Solution lots of substances (solute) dissolved in water (solvent).

13 Osmosis—Cont. Osmotic concentration - concentration of all solutes in an Aqueous solution Isosmotic – solute concentrations are equal Hyperosmotic – solution with the higher solute concentration Hyposmotic – solution with the lower solute concentration

14 Active Transport Active transport requires energy (ATP’s) to move a substance against its concentration gradient. Involves highly selective protein carriers within the membrane Allows cells to maintain specific ions or molecules at cytoplasmic concentration that are higher or lower than in the extra-cellular fluid. Example of an active transport mechanism Sodium-potassium pump 1/3 of all ATP’s used by a cell fuels this pump

15 Endocytosis - enveloping food – phagocytosis - material taken in is in particulate form – pinocytosis - material taken in is in liquid form Exocytosis - discharge of material from vesicles at the cell surface

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17 1.Apa perbedaan plasmolisis, krenasi dan lisis?

18 a.Lisis : hancurnya sel karena rusaknya atau robeknya membran plasma. b.Krenasi : sel berkeriput karena kekurangan air c.Plasmolisis : peristiwa lepasnya membran plasma dari dinding sel d. Osmosis adalah perpindahan ion atau molekul air (pelarut) dari kerapatan tinggi ke kerapatan rendah dengan melewati suatu membran (disebut juga difusi lewat membran)

19 2. Mengapa peristiwa pompa Na+ dan K+ termasuk transpor aktif? Jelaskan!

20 Mekanisme pompa Na+ - K+ 1.ATPase mengikat Na+ pada permukaan sitoplasmik ® mengakibatkan ATPase menghidrolisa ATP ® ADP + P + E. 2.ATPase mengalami fosforilasi. 3.Terjadi perubahan konfigurasi dari ATPase ® Na+ ditranspor keluar sel. 4.ATPase mengikat K+ pada permukaan ekstra seluler. 5.ATPase mengalami defosforilasi. 6. ATPase kembali pada posisi semula. K+ ditranspor ke dalam sel. 2. Pompa Na+ dan K+ termasuk transpor aktif sebab: -terjadi perpindahan zat dari konsentrasi rendah ke konsentrasi tinggi -perpindahan zat melawan gradien konsentrasi membuthkan energi

21 EXPERIMENTAL

22 Diffusion, Osmosis, Plasmolisis, Crenation Materials Sum Allium cepa 2 (bawang merah) Solanum tuberosum 2 (kentang) Pheretima sp. 2 (cacing tanah) Rhoe discolor 1 (adam hawa) Ink (tinta) 1 bottle Bottle2 Sugar insufficient Silet