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Unformatted text preview: Intro Bio I (BIO 311C), Fall 2009, Dr. Bushart Homework #4 1. Why would you not expect to find dUTP in cells? Uracil containing bases are used in RNA but not DNA. The d prefix indicates that the nucleotide has a deoxyribose, which are the subunits of DNA and not RNA. (By similar comparison, TTP would be unlikely as well, it should only be found as dTTP. dUTP does have artificial applications in research though.) 2. Amylose and cellulose are both made of glucose so why are amylose fibers helical while cellulose fibers are straight? Explain more than just the names of the bonds. Amylose uses -1,4-glycosidic bonds while cellulose uses -1,4-glycosidic bonds. Part of what the naming refers to is the location of the hydroxyl group on carbon 1. Notice that the bond formed in amylase has the sugar units oriented in the same direction while in cellulose each monomer is upside-down in relation to the next one in line. By having the bonds and sugars all lined up in the same orientation as in amylose, the fiber becomes helical due to the total sum of small angles in each glycosidic bond. In cellulose, however, the angles cancel out since each one points in the opposite direction from its neighbor. The end result is that cellulose fibers then appear to be essentially straight while amylose curves. 3. Cell membranes are self healing, meaning if a membrane was torn, it would automatically re-seal to form a closed compartment. Explain why this is so. This has to do with the very same forces that lead to the formation of sealed compartments to begin with. A tear in the membrane will expose the hydrophobic core of the bilayer to water, an interaction that is not favorable. The lowest energy state is for the bilayer to water, an interaction that is not favorable....
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