CH339L.09.Test1.Key - CH339L.09.Test.1 Name l4 l(1 10...

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Unformatted text preview: CH339L.09.Test.1 Name l4 l: (1; 10 points) Based on the numbering of the purine ring system, what order were the atoms added during de novo purine biosynthesis? The answer should be in the following form: 1 --> 2 --> 3 --> [4,5,7] —-> 6 --> 8 --> 9 (incidentally, this is a wrong answer) 9901!»le '“> 8 ~> are t. ——> ("7" L (2; 10 points) In some Martian organisms, thymidine is made in a manner similar to uridine, but starting from an aspartate derivative. Draw the structure of the aspartate derivative. HCJC‘ C HgN Ct,le (3; 10 points) In some real Earth organisms, thymidine is made via a different version of thymidylate synthase, known as ThyX, which has a flavin cofactor. The products of the ThyX reaction are: (a) Dihydrofolate, thymidine, and FADH2 (E) Tetrahydrofolate, thymidine, and FAD (c) Tetrahydrofolate, thymidine, and FADH2 (d) Dihydrofolate, thymidine, and FAD (4; 15 points) The regulation of nucleoside biosynthesis is even more complex than you've so far seen. For example, a 2005 paper (Som et al.) suggested that: "Experiments from the Daignan-Fornier laboratory showed that intermediates in the de novo purine nucleoside biosynthetic pathway, SAlCAR and AlCAR, are likely to be the intracellular signals needed for @/ inactivation] of the ADE genes (involved in purine and adenine biosynthesis). The levels of these biosynthetic intermediates were proposed to reflect levels of the nucleotide pools indirectly through regulating the activity of the first enzyme of the pathway, glutamine-5-phosphoribosyI-1—pyrophosphate amidotransferase, by ATP. Feedback [activation / i@] by ATP [increases / @951 pathway flux . d leads to [high /@ levels of SAlCAR and AlCAR. When feedback [activation / in] is reversed, flux through the pathway [is/ decreases] and the SAlCAR /AlCAR signal is generated, leading to an [@e/ decrease] in the transcription of the ADE genes." Circle the correct words. Keep in mind that SAlCAR and AlCAR are intermediates in the pathway. (5; 20 points) During the biosynthesis of several cofactors. guanosine is ring opened with the loss of its 8 carbon. Draw the missing intermediate; push arrows to show how it was made. O O H\N N N N O OH OH O l H t (f NH ’ \N 2 N \ HO KN + HCOOH K H0 £in H20 (6; 10 points) 5—hydroxymethyl cytidine is a modified base that is frequently found in nature. Which folate derivative is used to make 5-methoxy cytidine from cytidine? (a) N10-formyl THF NH; (b) N5-methyl THF N I OH @3 N5, N10 methylene THF OH 2\ i O N 0 (d) N5, N10 methenyl THF ' HO'if—O 0 if Q HO (7; 30 points) it has been suggested that since the adenine phosphoribosyl transferase activity in patients suffering from Lesch-Nyhan syndrome is normal or even elevated, an alternate reclamation route for guanine may exist, ameliorating the effects of the disease. A reaction pathway that would lead guanosine into salvage via adenine phosphoribosyl transferase is shown below. Draw the intermediates Z and Y, and name the cofactors, substrates, and products A, B, and C. In your drawings you can just label the ribose as R5P, rather than drawing it, but you must draw the nucleobases. A B A,C Aspartate, GTP Pi Guanosine 3:» Z g YLs—> Adenosine —\-b-—> Adergne+ \' Rl,5 iP Fumarate, GDP + Pi NH3 P: E v i N l (8; 15 points) Draw the structure of the phosphorylated intermediate in the two—step reaction catalyzed by GAR sythetase. ‘ ' / .2 ' "3 ~— .7} N Ha L \ll b P r ...
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This note was uploaded on 10/21/2009 for the course CH biochemist taught by Professor Kaplan during the Spring '09 term at University of Texas.

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CH339L.09.Test1.Key - CH339L.09.Test.1 Name l4 l(1 10...

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