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The document summarizes key concepts about membrane structure and function from Chapter 7. It describes the fluid mosaic model of membranes, which proposes that membranes are made of a phospholipid bilayer with various proteins embedded within. Membranes exhibit selective permeability and fluidity. Integral membrane proteins carry out important functions like transport, signaling, and cell recognition. Membranes are synthesized in the ER and Golgi apparatus, giving them distinct inner and outer compositions.Read less

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Cấu trúc màng tế bào english

• 1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 7 Membrane Structure and Function
• 2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Life at the Edge • The plasma membrane is the boundary that separates the living cell from its nonliving surroundings • The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others
• 3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteins • Phospholipids are the most abundant lipid in the plasma membrane • Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions • The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it
• 5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Models: Scientific Inquiry • Membranes have been chemically analyzed and found to be made of proteins and lipids • Scientists studying the plasma membrane reasoned that it must be a phospholipid bilayer • In 1972, Singer and Nicolson proposed that the membrane is a mosaic of proteins dispersed and individually inserted into the phospholipid bilayer
• 6. LE 7-2 Hydrophilic head Hydrophobic tail WATER WATER
• 7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In 1935, H. Davson and J. Danielli proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins • Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions • In 1972, Singer and Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water
• 8. LE 7-3 Hydrophilic region of protein Hydrophobic region of protein Phospholipid bilayer
• 9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Freeze-fracture studies of the plasma membrane supported the fluid mosaic model • Freeze-facture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer
• 10. LE 7-4 Knife Cytoplasmic layerExtracellular layer Cytoplasmic layer Plasma membrane Extracellular layer Proteins
• 11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Fluidity of Membranes • Phospholipids in the plasma membrane can move within the bilayer • Most of the lipids, and some proteins, drift laterally • Rarely does a molecule flip-flop transversely across the membrane
• 12. LE 7-5a Lateral movement (~107 times per second) Flip-flop (~ once per month) Movement of phospholipids
• 13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • As temperatures cool, membranes switch from a fluid state to a solid state • The temperature at which a membrane solidifies depends on the types of lipids • Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids • Membranes must be fluid to work properly; they are usually about as fluid as salad oil
• 14. LE 7-5b ViscousFluid Unsaturated hydrocarbon tails with kinks Membrane fluidity Saturated hydro- carbon tails
• 15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The steroid cholesterol has different effects on membrane fluidity at different temperatures • At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids • At cool temperatures, it maintains fluidity by preventing tight packing
• 16. LE 7-5c Cholesterol Cholesterol within the animal cell membrane
• 17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some proteins in the plasma membrane can drift within the bilayer • Proteins are much larger than lipids and move more slowly • To investigate whether membrane proteins move, researchers fused a mouse cell and a human cell
• 18. LE 7-6 Membrane proteins Mixed proteins after 1 hourHybrid cell Human cell Mouse cell
• 19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Proteins and Their Functions • A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer • Proteins determine most of the membrane’s specific functions • Peripheral proteins are not embedded • Integral proteins penetrate the hydrophobic core and often span the membrane
• 20. LE 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Microfilaments of cytoskeleton Cholesterol Integral protein Peripheral proteins CYTOPLASMIC SIDE OF MEMBRANE EXTRACELLULAR SIDE OF MEMBRANE Glycolipid
• 21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Integral proteins that span the membrane are called transmembrane proteins • The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into alpha helices
• 22. LE 7-8 EXTRACELLULAR SIDE N-terminus C-terminus CYTOPLASMIC SIDE α Helix
• 23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Six major functions of membrane proteins: – Transport – Enzymatic activity – Signal transduction – Cell-cell recognition – Intercellular joining – Attachment to the cytoskeleton and extracellular matrix (ECM)
• 24. LE 7-9a Enzymes Signal Receptor ATP Transport Enzymatic activity Signal transduction
• 25. LE 7-9b Glyco- protein Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extra- cellular matrix (ECM)
• 26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Role of Membrane Carbohydrates in Cell-Cell Recognition • Cells recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane • Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins) • Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual
• 27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Synthesis and Sidedness of Membranes • Membranes have distinct inside and outside faces • The asymmetrical distribution of proteins, lipids and associated carbohydrates in the plasma membrane is determined when the membrane is built by the ER and Golgi apparatus
• 28. LE 7-10 Plasma membrane: Cytoplasmic face Extracellular face Transmembrane glycoprotein Plasma membrane: Secreted protein Vesicle Golgi apparatus Glycolipid Secretory protein Transmembrane glycoproteins ER

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