Homework_4_01-14-09_C&A

Homework_4_01-14-09_C&A - Biology 5A Homework 4...

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Biology 5A Homework 4 January 14-16, 2009 1. Much of the strength of the hard white enamel of teeth is due to hydroxyapatite, an aggregated form of calcium phosphate. This calcium phosphate is held together by ionic bonds between the calcium cation, Ca +2 , and the phosphate anion, R-O-PO 3 -2 . To thoroughly clean the surface of a tooth in preparation for gluing on a bracket, orthodontists briefly apply an etching solution that dissolves away a thin surface layer of enamel. The etching solution works by adjusting the pH to a value where the phosphate groups are electrically neutral and thus unable to participate in ionic bonding with calcium. To be most effective as an etching solution, the pH of the solution should be: A. pH < (1 to 2). B. (1 to 2) < pH < (2 to 4). C. (2 to 4) < pH < (6 to7). D. (6 to 7) < pH < (9 to 10). E. pH > (9 to 10) (Ans. A) 2. The molecule shown in the figure is called cystine and is formed by joining together two identical molecules called cysteine.
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Homework_4_01-14-09_C&amp;amp;A - Biology 5A Homework 4...

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