Review 6 Membrane Structure Answers will not be provided Fill in the blanks in the following statements 1 are compounds that are insoluble in water and but soluble in nonpolar organic solvents 2 Classified according to their chemical nature lipids fall into two main groups One group which consist of open chain compounds with polar head groups and long nonpolar tails includes fatty acids phospholids The second major group consists of fused ring compounds the steroids an important representative of this group is cholesterol 3 Lipid molecules in biological membranes are arranged as a continuous double layer called the which is about 5 nm thick 4 All the lipids found in membranes are said to be because they have one hydrophilic end and one hydrophobic end 5 When amphipathic molecules are placed in an aqueous environment they tend to aggregate so as to bury their hydrophobic ends and expose their hydrophilic ends to water giving rise to two different kinds of structures either spherical or planar with the hydrophobic tails sandwiched between the hydrophilic head groups 6 Cell membranes consist mainly of and also contain that are linked to lipids and proteins 7 Unsaturated fatty acids usually have double bonds 8 Eukaryotic plasma membranes contain especially large amounts of which enhances the mechanical stability of the lipid bilayer 9 The most useful agents for disrupting hydrophobic associations and destroying the bilayer are which are small amphipathic molecules that tend to form micelles in water 10 Sugar containing lipids called are found only in the outer half of the bilayer and their sugar groups are exposed at the cell surface 11 The association of membrane proteins with lipids in the membrane bilayer always involves a electrostatic interactions b hydrophobic interactions c covalent linkages d all of the above 12 Biosynthetic enzymes bound to the cytosolic monolayer of the ER membrane produce new phospholipids from free fatty acids and insert them into the cytosolic monlayer Enzymes called scramblases then randomly transfer phospholipid molecules from one monolayer to the other allowing the membrane to grow as a bilayer When membranes leave the ER and are incorporated in the Golgi they encounter enzymes called flippases which selectively remove phosphatidylserine and phosphatidylethanolamine from the noncytosolic monolayer and flip them to the cytosolic side This transfer leaves phosphatidylcholine and sphingomyelin concentrated in the noncytosolic monolayer 13 We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest bleaching the label in one small area and then measuring the speed of signal recovery as molecules migrate back into the bleached area What is this method called What does the abbreviation stand for a SDS b SPT c GFP d FRAP 14 Cell membranes are fluid and thus proteins can diffuse laterally within the lipid bilayer However sometimes the cell needs to localize proteins to a particular membrane domain Name three mechanisms that a cell can use to restrict a protein to a particular place in the cell membrane 15 There are several ways that membrane proteins can associate with the cell membrane Membrane proteins that extend through the lipid bilayer are called proteins and have regions that are exposed to the interior of the bilayer On the other hand membrane associated proteins do not span the bilayer and instead associate with the membrane through an helix that is Other proteins are attached to lipid molecules that are inserted in the membrane membrane proteins are linked to the membrane through noncovalent interactions with other membrane bound proteins 16 Please understand Common Features of Biological Membranes 17 Plant membranes have a higher percentage of unsaturated fatty acids than animal membranes Animal membranes are less or more fluid than plant membranes 18 Membrane Fluidity is controlled by fatty acid composition and cholesterol content The membranes of prokaryotes which contain no appreciable amounts of steroids are the most fluid True or false 19 Glycolipids on the surface of cells are especially important as cell markers True or false 20 Membranes are transported by a process of vesicle budding and fusing Here a vesicle is shown budding from the Golgi apparatus and fusing with the plasma membrane Note that the orientations of both the membrane lipids and proteins are preserved during the process the original cytosolic surface of the lipid bilayer green remains facing the cytosol and the noncytosolic surface red continues to face away from the cytosol toward the lumen of the Golgi or transport vesicle or toward the extracellular compartment Similarly the glycoprotein shown here remains in the same orientation with its attached sugar facing the noncytosolic side
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