BSC2010 Exam 2 Study Guide Chapter 7 Vocabulary Selective permeability a property of biological membranes that allows them to regulate the passage of substances across them Fluid mosaic model the currently accepted model for cell membrane structure which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids Diffusion the spontaneous movement of a substance down its concentration or electrochemical gradient from a region where it is more concentrated to a region where it is less concentrated Concentration gradient a region along which the density of a chemical substance increases or decreases Osmosis the diffusion of free water across a selectively permeable membrane Facilitated diffusion the passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific trans membrane transport protein requiring no energy expenditure Ion channel a trans membrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient o particular stimulus Gated channel a trans membrane protein channel that opens or closes in response to a Active transport the movement of a substance across a cell membrane against its concentration or electrochemical gradient mediated by specific transport proteins and requiring an expenditure of energy Sodium potassium pump a transport protein in the plasma membrane of animal cells that actively transport sodium out of the cell and potassium into the cell Membrane potential the difference in electrical charge voltage across a cells plasma membrane due to the differential distribution of ions Membrane potential affects the activity of excitable cells and the trans membrane movement of all charged substances Electrochemical gradient the diffusion gradient of an ion which is affected by both the concentration difference of an ion across a membrane a chemical force and the ion s tendency to move relative to the membrane potential an electrical force Proton pump an active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient generating a membrane potential in the process Co transport the coupling of the downhill diffusion of one substance to the uphill transport of another against its own concentration gradient Exocytosis the cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane Endocytosis cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane Ligand a molecule that binds specifically to another molecule usually a larger one Phospholipid A lipid made up of glycerol joined to two fatty acids and a phosphate group The hydrocarbon chains of the fatty acids act as nonpolar hydrophobic tails while the rest of the molecule acts as a polar hydrophilic head Phospholipids form bilayers that function as biological membranes Understanding homework 1 What is true of a typical plasma membrane a The two sides of the plasma membrane have different lipid and protein composition i Because the membrane serves different functions on the cytoplasmic and exterior surfaces the structure and composition of the surfaces must be different 2 Singer and Nicolson s fluid mosaic model of the membrane proposed that a Membranes consist of protein molecules embedded in a fluid bilayer of phospholipids 3 What are major structural components of the cell membrane a Phospholipids and proteins 4 The presence of cholesterol in the plasma membranes of some animals a Enables the membrane to stay fluid more easily when cell temperature drops 5 What is a way in which the membrane of winter wheat is able to remain fluid even when it is extremely cold a By increasing the percentage of unsaturated phospholipids in the membrane 6 What is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures packing tightly a The double bonds form kinks in the fatty acid tails preventing adjacent lipids from 7 What is something that is true of integral membrane proteins a They are usually trans membrane proteins 8 What are some examples of things that can be found in hydrophobic portion of the lipid bilayer a Trans membrane proteins integral proteins glycoproteins integrin i NOT found in the bilayer peripheral proteins 9 Why are lipids and proteins free to move laterally in membranes a There are only weak hydrophobic interactions in the interior of the membrane 10 What is a common characteristic of a carrier protein in a plasma membrane a It exhibits a specificity for a particular type of molecule 11 If starch CO2 glucose an amino acid and potassium are present within a molecule which of these would move through the lipid bilayer of the plasmas membrane most rapidly a CO2 12 What is true about osmosis a The presence of aporin s proteins that form water channels in the membrane should speed up the process of osmosis i Aquaporin s facilitate water movement across membranes and thus speed up the process of osmosis 13 Water passes quickly through cell membranes because a It moves through aquaporin s in the membrane Aquaporins A channel protein in the plasma membrane of a plant animal or microorganism cell that specifically facilitates osmosis the diffusion of free water across the membrane 14 Mammalian blood contains the equivalent of 0 15 M NaCl Seawater contains the equivalence of 0 45 M NaCl What will happen if red blood cells are transferred to seawater a Water will leave the cells causing them to shrivel and collapse i They are entering an area of a higher concentration which causes them to shrivel ii 15 The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which process a Co transport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis i Movement of solutes against their concentration gradient couples the movement of one solute down its concentration gradient to the movement of another glucose in this case against its concentration gradient 16 How to active and passive transports of solutes across a membrane typically differ a Active transport always involves the utilization of cellular energy whereas passive transport does not require cellular energy i Active and passive transport can be
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