AS Biology cell membranes

AS Biology cell membranes - AS Biology FOUNDATION Chapter 4...

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Unformatted text preview: AS Biology FOUNDATION Chapter 4 CELL MEMBRANES and TRANSPORT AS Biology. Foundation. Cell membranes and Transport 1 The Cell AS Biology. Foundation. Cell membranes and Transport 2 Learning Objectives 1. Describe the fluid mosaic model of membrane structure and explain the underlying reasons for this structure. 2. Outline the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes. 3. Outline the roles of the plasma membrane, and the roles of membranes within cells. 4. Describe and explain how molecules can get in and out of cells (cross cell membranes) by the processes of diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis. 5. Describe the effects on animal and plant cells of immersion in solutions of different water potential. 6. Describe the features of the gaseous exchange surface of mammalian lung. 7. Describe the features of root hairs that enable the uptake of ions by active transport. AS Biology. Foundation. Cell membranes and Transport 3 Key words you should know Phospholipids Solution Polar Solute Hydrophilic Solvent Hydrophobic Partially permeable Micelles Water potential Phospholipid bilayer Solute Potential Fluid mosaic model Pressure Potential Glycoproteins Turgid Glycolipids Plasmolysis Cholesterol Plasmolysed Proteins Incipient plasmolysis Transport proteins Active transport Enzymes Carrier protein Receptor molecules Bulk transport Diffusion Endocytosis Concentration gradient Phagocytosis Facilitated diffusion Phagocytes Osmosis Phagocytic vacuoles Root hair Surface area Pinocytosis Micropinocytosis Exocytosis Gaseous exchange Alveoli Epidermis Passive transport AS Biology. Foundation. Cell membranes and Transport 4 Cell membrane All living things are surrounded by a membrane. A cell membrane is also known as plasma membrane. Controls exchange of materials such as nutrients and waste between cells and their environment. Has other important functions for example to enable cells to receive hormones. To understand the function of anything in biology, you must study the structure first! AS Biology. Foundation. Cell membranes and Transport 5 Cell Membranes from Opposing Neurons (TEM x436,740). Nerve cell Gap between cells cell membrane Cell membrane { } 7nm wide Nerve cell AS Biology. Foundation. Cell membranes and Transport 6 Cell membranes are made of Cell PHOSPHOLIPIDs PHOSPHOLIPIDs HYDROPHILIC heads HYDROPHILIC (water liking) (water -Attracted to the water -Attracted called POLAR HYDROPHOBIC tails HYDROPHOBIC (water fearing) (water -Not attracted to the -Not water water called NON-POLAR A Phospholipid AS Biology. Foundation. Cell membranes and Transport 7 Phospholipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO4­) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two nonpolar "tails". AS Biology. Foundation. Cell membranes and Transport 8 A phospholipid HYDROPHILIC HEAD At the other end of the phospholipid is a phosphate group and several double bonded oxygens. The atoms at this end of the molecule are not shared equally. This end of the molecule has a charge and is attracted to water. It is POLAR HYDROPHOBIC TAILS The two long chains coming off of the bottom of this molecule are made up of carbon and hydrogen. Because both of these elements share their electrons evenly these chains have no charge. They are NON POLAR. Molecules with no charge are not attracted to water; as a result water molecules tend to push them out of the way as they are attracted to each other. This causes molecules with no charge not to dissolve in water. 3D model of a Phospholipid AS Biology. Foundation. Cell membranes and Transport 9 A Phospholipid Bilayer Phospholipids can form: Phospholipids BILAYERS BILAYERS -2 layers of phospholipids -2 with with hydrophobic tails protected inside by the hydrophilic heads. hydrophilic The PHOSPHOLIPID BILAYER is the basic structure of membranes. AS Biology. Foundation. Cell membranes and Transport 10 AS Biology. Foundation. Cell membranes and Transport 11 Structure of the cell membrane Phospholipids Cell membranes are made mainly of Cell phospholipids. They have: phospholipids. HYDROPHILIC heads (water liking) -Attracted to the water POLAR HYDROPHOBIC tails (water fearing) -Not attracted to the water NON-POLAR Phospholipids can form BILAYERS -2 layers of phospholipids with hydrophobic tails protected hydrophobic inside by the hydrophilic inside heads. heads. The PHOSPHOLIPID BILAYER is the basic structure of membranes. the AS Biology. Foundation. Cell membranes and Transport 12 Diagram representing the cell membrane Remember the membrane is 7nm wide AS Biology. Foundation. Cell membranes and Transport 13 Fluid mosaic model Cell membranes also contain proteins within the phospholipid bilayer. This ‘model’ for the structure of the membrane is called the: FLUID MOSAIC MODEL FLUID­ because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC­ because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. AS Biology. Foundation. Cell membranes and Transport 14 Diagram of a cell membrane AS Biology. Foundation. Cell membranes and Transport 15 TEM of freeze­fractured cell membrane. The fracture occurs between the two phospholipid layers. You can clearly see the exposed proteins sticking out of the two layers. Individual phospholipids are too small to see. AS Biology. Foundation. Cell membranes and Transport 16 Cell Membranes from Opposing Neurons (TEM x436,740). } Phospholipid Bilayer 7nm wide AS Biology. Foundation. Cell membranes and Transport 17 Features of the fluid mosaic model Double layer – BILAYER of phospholipids which can move about by ………………………… in their own ………………………. Phospholipid tails point inwards forming a ……. ………. ………………………… interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane. Some phospholipids fatty acid tails are ……………………….. – straight so fit together tightly. Some are ………………………… – bent so fit together ……………………. The more unsaturated tails there are the more ……………… the membrane becomes. The lower the temp, the ……………….fluid. Most protein molecules …………………. like icebergs in the layers, some are fixed to ………………………. inside the cell and don’t float. Some proteins are embedded in the outer layer, some in the inner layer and some ………………… the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the …………………………… and ………………………….. portions of the ……………………………… of the membrane. This ensures the proteins stay in the membrane. The membrane is ……nm thick on average. Some phospholipids have carbohydrates attached to them called­ …………………….. Some of the proteins have carbohydrates attached to them called– …………………… The membrane also contains molecules of ……………………………….. AS Biology. Foundation. Cell membranes and Transport 18 18 Features of the fluid mosaic model Double layer – BILAYER of phospholipids which can move about by DIFFUSION in their own MONOLAYER Phospholipid tails point inwards forming a NON­POLAR HYDROPHOBIC interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane. Some phospholipids fatty acid tails are SATURATED – straight so fit together tightly. Some are UNSATURATED – bent so fit together loosely. The more unsaturated tails there are the more ‘fluid’ the membrane becomes. The lower the temp, the less fluid. Most protein molecules float like icebergs in the layers, some are fixed to structures inside the cell and don’t float. Some proteins are embedded in the outer layer, some in the inner layer and some span the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the Hydrophobic and Hydrophilic portions of the phospholids of the membrane. This ensures the proteins stay in the membrane. The membrane is 7nm thick on average. Some phospholipids have carbohydrates attached to them – GLYCOLIPIDS Some of the proteins have carbohydrates attached to them – GLYCOPROTEINS The membrane also contains molecules of CHOLESTEROL AS Biology. Foundation. Cell membranes and Transport 19 19 Roles of components of cell membranes Using the following headings produce a table on A4 to summarise roles of t he different types of molecules found in the cell membrane. Try not to copy, pick different out the relevant information and write it in note form You may want to use out bullet points, different coloured pens etc basically whatever helps you to remember them. remember There will be a short test on this next lesson! Use pages 53-54. Component Function 1. 1. Phospholipids 2. Cholesterol 3. Proteins 4. Glycolipids and Glycoproteins AS Biology. Foundation. Cell membranes and Transport 20 20 Summary Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER. Phospholipds have HYDROPHOBIC (non­polar) tails and HYDROPHILIC (polar) heads. The best model of the cell membrane is called the FLUID MOSAIC MODEL The average thickness of the membrane is 7nm. The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent) Proteins can float or be fixed and also have hydrophobic and hydrophilic portions. Some proteins and phospholipids have carbohydrates attached to them to form GLYCOPROTEINS AND GLYCOLIPIDS. Phospholipids form the bilayer, act as barrier to most water soluble substances Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane. Proteins act as transport proteins to act as channels for substances to move into or out of the cell. Some act as membrane enzymes and some have important roles in membranes of organelles. Glycolipids and Glycoproteins help to stabilise membrane structure, some act as receptor molecules eg for hormones and neurotransmitters or as antigens for other cells to recognise them. AS Biology. Foundation. Cell membranes and Transport 21 Movement of selected molecules across the cell membrane AS Biology. Foundation. Cell membranes and Transport 22 Moving amoeba AS Biology. Foundation. Cell membranes and Transport 23 This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching. AS Biology. Foundation. Cell membranes and Transport 24 ...
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This note was uploaded on 11/07/2011 for the course BIOLOGY 100 taught by Professor Staff during the Winter '08 term at BYU.

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