23 - Wednesday, October 20, 2010 Lecture 23 Announcements:...

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Wednesday, October 20, 2010 Lecture 23 Announcements: 1. Reminder: the midterm exam will take place tomorrow night starting at 7:30PM. Room assignments: in Baker 200, last names A – T in Baker 219, last names U - Z 2. Re answer key to 2009 midterm exam on Blackboard: Windows users have not been able to see the correctly formatted answer key graph for problem #13, the Lineweaver-Burk question. A new pdf version of the answer key solves this problem, and is now up on Blackboard. Monday's lecture: Carbohydrate basics Carbohydrate roles in energy storage polymers and in structure Today's lecture: Page 165 c. Glycosaminoglycans - The "proteoglycans" of the extracellular matrix are made of proteins (the minor component) and heteropolysaccharide glycosaminoglycans (major component). The latter are polymers of repeating disaccharides. Notice on page 165 that glycosaminoglycans (left side of page) are very negatively charged. Thus, these molecules repel each other. Being highly polar and also charged, they bind lots of water. They form a loose mesh. Located immediately outside cells, this loose mesh allows all small molecules and even many big molecules (proteins, hormones, for example) to penetrate to the cell surface and bind to receptor proteins in the membrane. In addition, glycosaminoglycans are “slippery,” since they bind a lot of water and repel both each other and negatively-charged surfaces, and thus serve as lubricating fluid in joints, and as mucous on other body surfaces. Note : Polysaccharides are not made from a template. They are always linked together by enzymes, with a different enzyme required for each different linkage. Thus, size of polysaccharides is not strictly fixed. Also, a given polysaccharide does not have a complex sequence, like proteins, RNA, or DNA, since only a few enzymes are involved in their synthesis. We do not know the 3-d structure of polysaccharides very well. Our methods for characterizing the 3-d structure of polysaccharides, or even just the sequence, are not as advanced as they are for proteins or nucleic acids.
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A proteoglycan is a structure of protein-linked glycosaminoglycans . It is mostly carbohydrate, but is also has some protein. (See drawing and pictures, right side of page 164). As to the structural role of proteoglycans, they are important in the extracellular matrix, p. 166. Their strong negative charge and extensive hydration create a porous matrix that allows both small molecules and proteins to diffuse to the cell surface. Unexpectedly, it happens that a chondroitin sulfate proteoglycan that proliferates in damaged tissue is a major block to nerve axon regeneration. Here is a case wherein detailed understanding of underlying carbohydrate structure can be of importance to human health. 3.
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This note was uploaded on 12/10/2011 for the course BCHEM 3350 taught by Professor Feig during the Fall '09 term at Cornell University (Engineering School).

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23 - Wednesday, October 20, 2010 Lecture 23 Announcements:...

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