20. All nucleotides are synthesized as mononucleotides. Which amino acid is not
ID: 49850 • Letter: 2
Question
20. All nucleotides are synthesized as mononucleotides. Which amino acid is not used for the synthesis of purine bases?
A. glycine B. asparagine C. glutamine D. aspartate E. All of the above.
22. The enzymes involved in the synthesis of pyrimidine nucleoside monophosphates are under multiple regulations. Which is not involved in the regulation?
A. UTP B. ATP C. GTP D. CTP E. None of the above.
50. Which is not related to regulation of gene activity?
A. Transcription factor binding close to the promoter regions.
B. SAM binding to mRNA.
C. Alterations in mRNA conformations by Trp availability.
D. All of these.
E. None of these.
Please explain your answers.
Explanation / Answer
B. asparagine . it is not involved in the purine synthesis.
Both adenine and guanine are derived from the nucleotide inosine monophosphate (IMP), which is the first compound in the pathway to have a completely formed purine ring system.
Inosine monophosphate is synthesized on a pre-existing ribose-phosphate through a complex pathway . The source of the carbon and nitrogen atoms of the purine ring, 5 and 4 respectively, come from multiple sources. The amino acid glycine contributes all its carbon (2) and nitrogen (1) atoms, with additional nitrogen atoms from glutamine (2) and aspartic acid (1), and additional carbon atoms from formyl groups (2), which are transferred from the coenzyme tetrahydrofolate as 10-formyltetrahydrofolate, and a carbon atom from bicarbonate (1). Formyl groups build carbon-2 and carbon-8 in the purine ring system, which are the ones acting as bridges between two nitrogen atoms.
2. E. None of the above. every NTP is under regulation. if not so the synthesis would have become unregulated.
3. E. None of these. , all of these activities are involved in regulation of gene activity.
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