Biomembran PDF

Biomembran Yanti Ivana Suryanto 1 Tujuan Pembelajaran Menjelaskan fungsi membran sel Menjelaskan susunan & komposisi membran sel Mengetahui klasifikasi membran sel 2 Why Membran? 3  General fun...

Biomembran Yanti Ivana Suryanto 1 Tujuan Pembelajaran Menjelaskan fungsi membran sel Menjelaskan susunan & komposisi membran sel Mengetahui klasifikasi membran sel 2 Why Membran? 3  General functions Physical barrier → separates ICF - ECF Physical isolation Control: Entry of ions & nutrient into cell Regulation of exchange Elimination cellular waste with the environment Release cell products Contain proteins → cell recognize & respond to molecules Communication between / changes in its external environment cells & its environment Alteration in cell membrane → affect cell’s activities Cytoskeleton → maintain cell shape Structural support Also create specialized junction between cell-cell and cell-extracellular matrix Supported by cell membrane structure 4 Membranes composition Early 20’th C → composition: lipids + proteins + carbohydrate ??? → highly variable properties of membrane in different types of cells → molecular arrangement / ratio protein : lipid More metabolic active a membrane, more proteins 5  1920s → enough lipid → double layer (bilayer) 1930s → presence of protein in bilayer 1960s → butter sandwich (introduction of electron microscopy) – lipids sandwiched between 2 dark layers of protein 1970s → freeze-fracture electron micrographs → three-dimensional arrangement of lipids & proteins within cell membranes → S.J. Singer & G.L Nicolson (1972) → fluid mosaic model of the membrane 6 7 8 Types of lipids Phospholipids Lipid terutama bertanggung jawab: high permeability thd lipid-soluble Sphingolipids substances (CO2, O2, asam lemak, hormone steroid); low permeability thd water-soluble Cholesterol substances (ion, glukosa, asam amino) 9  Komponen fosfolipid membran plasma Phospholipids 1 Glycerol + 2 fatty acid chains + phosphate 10 Phospholipids In aqueous solution 11  Phospholipid bilayer Lodish H, Berk A, Zipursky SL, et al. New York: W. H. Freeman; 2000. 12  Sphingolipids Tail : Fatty acid Head: phospholipids / glycolipids Sphingolipids slightly longer than phospholipids 13  Cholesterol Hydrophobic Insert themselves between hydrophilic head of phospholipids Helps membrane impermeable to small water-soluble molecules Keep membranes flexible over a wide range of temperature 14 Membrane Proteins 15 Classification protein based on function Structural proteins Enzymes Receptors Transport proteins 16 Structural PROTEIN Transmembrane proteins Integral protein Membrane Lipid anchored Proteins proteins Peripheral proteins 17  Integral proteins - transmembrane Transmembrane proteins / membrane-spanning proteins Extend all the way across cell membrane Carbohydrates attach to extracellular loops Phosphate attach to intracellular loop To alter protein function → phosphorylation of proteins Cross the membrane once – 12 times 18 Integral proteins – lipid anchoring proteins Some bound to lipid tail Some on external surface of the cell (held by GPI {anchor [consist of membrane lipid + sugar-phosphate chain]) Found in association with membrane sphingolipids → lipid rafts Polarity → different faces of the cell have different protein → different properties 19  Functions of protein as Structural They help create cell junctions that hold tissues together, such as tight junctions and gap junctions They connect the membrane to the cytoskeleton to maintain the shape of the cell. The microvilli of transporting epithelia are one example of membrane shaping by the cytoskeleton They attach cells to the extracellular matrix by linking cytoskeleton fibers to extracellular collagen and other protein fibers [p. 96] 20 Protein as enzyme Membrane enzymes catalyze chemical reactions that take place either on the cell’s external surface or just inside the cell. Example: Enzymes on the external surface of cells lining the small intestine are responsible for digesting peptides and carbohydrates. Enzymes attached to the intracellular surface of many cell membranes play an important role in transferring signals from the extracellular environment to the cytoplasm 21  Protein as Receptor Membrane receptor proteins are part of the body’s chemical signaling system. The binding of a receptor with its ligand usually triggers another event at the membrane Sometimes the ligand remains on the cell surface, and the receptor-ligand complex triggers an intracellular response. In other instances, the receptor-ligand complex is brought into the cell in a vesicle Membrane receptors also play an important role in some forms of vesicular transport 22 Transport protein Transport proteins—moves lipophobic molecules across membranes Classification 1 the ATP-binding cassette (ABC) superfamily → use ATP’s energy to transport small molecules or ions across membranes the solute carrier (SLC) superfamily → include most facilitated diffusion transporters as well as some active transporters 23 Transport protein Classification II Channel proteins create water-filled passageways that directly link the intracellular and extracellular compartments. Carrier proteins, also just called transporters, bind to the substrates that they carry but never form a direct connection between the intracellular fluid and extracellular fluid. 24 25 26 27 Membrane carbohydrates Sugar attached to membrane protein → Glycoprotein → body immune response [ABO blood groups] Sugar attached to membrane lipids → Glycolipids Form protective layer → Glycocalyx 28 Concept map of cell membrane components 29 Structural support Cell – cell adhesions → Cell junctions Cell junctions hold cells together to form tissue Cell adhesion molecules (CAM) → membrane-spanning proteins responsible for cell junctions & transient cell adhesions 30 31 Cell junctions can be grouped into three categories: (b) Gap junctions which allow direct cell to cell communication, (c) tight junctions that block movement of material between cells, and (d) anchoring junctions that hold cells to one another and to the extracellular matrix 32  Property of membrane Membrane cell classification Property of substance: size & lipid solubility Permeable Allow substance pass through Semi-permeable Impermeable Not allow substance pass through 33 34 35 36 37 38 39 Homeostasis Homeostasis ≠ equilibrium. The intracellular and extracellular compartments of the body are in osmotic equilibrium, but in chemical and electrical disequilibrium. Furthermore, osmotic equilibrium and the two disequilibria are dynamic steady states. The goal of homeostasis is to maintain the dynamic steady states of the body’s compartments 40  Silverthorn, D.E. 2016, Human Physiology: An Integrated Approach, 7th ed, Pearson (https://slideplayer.com/slide/7287379/) 41