Week 5 Review Sheet answers

Week 5 Review Sheet answers - Final Review Sheet Week 5...

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Final Review Sheet – Week 5 Lecture 11 Main Points: The book describes a number of roles that membranes play. I included most of them on my cartoon. A major point to note, though, is that these roles generally apply to all membranes of the cell, internal or external (except cell-cell communication). Phosphoglycerides make up the bulk of the lipids in the membrane. It is their amphipathic structure that forms the bilayer. You should be familiar with the basic structure of these molecules. Other lipids include sphingolipids, including those with attached carbohydrates – the glycolipids – and cholesterol. The basic structure of the bilayer is a function of the amphipathic nature of the phospholipids, since the polar head groups on the outside can interact with water and the hydrophobic tails in the center are away from the water. Solutions of phospholipids (in organic solvents) squirted into water will spontaneously form phospholipid bilayer spheres, liposomes. These form again because of the action of the amphipathic phospholipids in water. They have been suggested as vehicles for drug delivery. Lipids above the transition temperature are fluid in a membrane. Increasing the unsaturations of the fatty acids in the phospholipids is an adaptation to allow organisms to maintain fluidity under colder body temperatures. The fluidity of the lipids is lateral only. Flip-flop, or the movement of a phospholipid from one face of the bilayer to the other essentially does not occur. Carbohydrates may be attached to proteins, making glycoproteins. Attachments are either at asparagines (N-linked) or at either serine or threonine (O-linked). These glycoproteins are always oriented with the sugar component facing outward. Note that the different ABO blood group antigens differ in the sugars found on a glycolipid ( the different alleles code for different enzymes that add N acetyl glucosamine – A group- or galactose– B. Type O has no enzyme so that there are no additions onto the basic oligosaccharide structure shared by all three.) There are three basic ways proteins can associate with the phospholipids bilayer. Integral proteins actually span the bilayer, which requires that they be structured differently from most proteins. They have regions of hydrophobic amino acids formed in a helix that spans the bilayer, with the hydrophobic groups pointed into the hydrophobic regions of the phospholipids. Peripheral proteins associate only through protein-protein interactions. They always reside within the water soluble sides of the membrane. They can be dissociated by disrupting their interactions with integral proteins (by using salt to disrupt ionic associations, for example). Lipid linked proteins are also seen. Here, the protein is covalently attached to a
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Week 5 Review Sheet answers - Final Review Sheet Week 5...

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