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Transcript
Sci 10. Ch 8 Cell Membranes CELL MEMBRANES ARE PHOSPHOLIPID BILAYERS MADE OF A DOUBLE LAYER OF PHOSPHOLIPIDS WHICH HAVE A HYDROPHOBIC FATTY ACID TAIL AND A HYDROPHILIC HEAD They also contain a) carbohydrate chains for cell to cell communication. These chains are attached to both lipids and proteins of the cell membrane. b) peripheral (surface) and integral proteins (spans the membrane). These proteins are crucial for transport of substances into and out of the cell. c) cholesterol maintains proper membrane flexibility, and also is crucial for cell signaling and nerve conduction. 3 jobs of the cell membrane 1. THE CELL MEMBRANE PROTECTS THE CELL ORGANELLES It’s a barrier: it keeps _____________________________________ out, keeps __________________ in. 2. THE CELL MEMBRANE HELPS WITH CELL ORGANIZATION. Organizes by surrounding and packaging materials into vesicles (i.e. lysosomes, endoplasmic reticulum, golgi apparatus). Organizes complex cellular chemical reactions like photosynthesis in the chloroplasts and cellular respiration in the mitochondria. 3. THE CELL MEMBRANE REGULATES WHAT GOES IN AND OUT OF THE CELL. a. Cell membrane is semipermeable: it is a selective filter that only lets certain substances in and out of cell. b. Regulates by particle size –molecules like oxygen and water are so small they can diffuse across the cell by slipping between the phospholipid molecules. c. Large or charged molecules can only be transported across the cell membrane by the membrane proteins. d. The cell is an OPEN SYSTEM (substances can enter and leave the cell). CELL MEMBRANE : FLUID MOSAIC MODEL The fluid mosaic model is used to describe cell membranes. All of the different molecules in the membrane = mosaic. The mosaic pieces are continually moving. This fluidity allows lipids, proteins, and carbohydrates to move within the membrane to where they are needed and it gives the membrane flexibility. cell membrane is a fluid mosaic http://www.youtube.com/watch?v=Rl5EmUQdkuI&feature=fvwrel : basic membrane stucturehttp://www.youtube.com/watch?v=GW0lqf4Fqpg&feature=related : shows membrane proteins receiving communications from hormones and sending this information inside the cell so it can carry out the instructions from the hormones. Identify by number in the diagram be the following structures (see pg. 293 in text) phospholipid bilayer filaments of cytoskeleton (draw in) peripheral protein integral protein cholesterol Exterior of the cell Interior of the cell Hydrophobic tails (lipids) Hydrophilic heads (phosphate) Layer 1 Layer 2 glycolipid (carbohydrate chain attached to membrane lipid) (draw in and label) glycoprotein (carbohydrate chain attached to cell membrane protein). (draw in and label) Learning Check! Test yourself! http://www.biology4kids.com/extras/quiz_cellmemb/index.html ASSIGNMENT: Answer the following questions: 1) Which of the following are open systems? a) a school cafeteria b) a sealed glass jar c) a cell d) a plant vacuole e) a closed metal box 2) Beet root cells can be used to study the effects of different solvents on membrane permeability. As each solvent dissolves the cell membrane, coloured pigments inside the cells leak out, tinting the solution. Slices of beet root were placed in three different solutions for 10 min. A special device was then used to measure the absorbance (measure of pigment concentration) in each solution, as shown below. Alcohol Absorbance for each alcohol concentration (%) Methanol Ethanol Propanol 0 250 250 250 20 300 270 262 40 500 350 299 60 625 453 366 80 625 630 500 100 625 628 600 a) Identify the manipulated, responding and control variables in this experiment. b) At lower concentrations, which alcohol was most damaging to beet cell membranes? c) Which alcohol appears to affect beet cell membranes the most? Explain how you arrived at your conclusion. 3) List 3 common household items that contain or have features of a semi-permeable membrane. Explain how the semi-permeability of each item relates to its function. 4) What would happen to a cell if its cell membrane were permeable rather than semipermeable?