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Chapter 26: Problem 1

Draw the purine and pyrimidine ring structures, indicating the metabolic source of each atom in the rings.

Short Answer

Expert verified
The purine ring comprises of a pyrimidine and an imidazole ring, with the atoms sourced from the amino acids glycine, aspartate, glutamine, from folic acid and carbon dioxide. The pyrimidine ring is a 6-membered ring primarily sourced from the amino acids aspartate and glutamine, and carbon dioxide.

Step by step solution

01

Drawing of Purine Ring

Begin by drawing the purine ring structure. It is comprised of a 6-membered pyrimidine ring fused to a 5-membered imidazole ring. Number the atoms in the rings starting from the Nitrogen of the pyrimidine ring, moving around the structure and then into the imidazole ring.
02

Indication of Metabolic Sources for Purine

Label the metabolic source of each atom in the purine structure. The atoms in the purine ring primarily come from the amino acids glycine (atoms 4, 5, 7), aspartate (atoms 1, 3, 9) and glutamine (atoms 3, 9), folic acid (atoms 2, 8), and carbon dioxide (atom 6).
03

Drawing of Pyrimidine Ring

Draw the pyrimidine ring structure next. This is a 6-membered ring with Nitrogen atoms at positions 1 and 3, and the remaining positions filled by Carbon atoms.
04

Indication of Metabolic Sources for Pyrimidine

Indicate the metabolic source of each atom in the pyrimidine ring. The atoms in the pyrimidine ring come mainly from the amino acids aspartate (atoms 2, 3, 4, 6) and glutamine (atom 1), and carbon dioxide (atom 5).

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Most popular questions from this chapter

The crystal structure of \(E\). coli dihydrofolate reductase (DFR) with NADP \(^{+}\) and folate bound can be found in the Protein Data Bank (www.rcsb.org/pdb) as file 7 DFR. Go to this website, enter "7DFR" in the search line, and click on "KiNG" under "Display options" when the 7 DFR page comes up. Explore the KiNG graphic of the DFR structure to visualize how its substrates are bound. (If you hold down the left button on your mouse and move the cursor over the image, you can rotate the structure to view it from different perspectives.) Note in particular the spatial relationship between the nicotinamide ring of \(\mathrm{NADP}^{+}\) and the pterin ring of folate. Do you now have a better appreciation for how this enzyme works? Note also the location of polar groups on the two substrates in relation to the DFR structure.

Write a balanced equation for the synthesis of dTMP from UMP and \(N^{5}, N^{10}\) -methylene-THF. Thymidylate synthase has four active-site arginine residues \(\left(\mathrm{Arg}^{23}, \mathrm{Arg}^{17 \mathrm{s}}, \mathrm{Arg}^{139}, \text { and } \mathrm{Arg}^{218}\right)\) involved in substrate binding. Postulate a role for the side chains of these Arg residues.

Describe the underlying rationale for the regulatory effects exerted on ribonucleotide reductase by ATP, dATP, dTTP, and dGTP.

(Integrates with Chapter \(15 .\) ) Unlike its allosteric counterpart glycogen phosphorylase (an \(\alpha_{2}\) enzyme), \(E\) coli ATCase has a heteromeric \(\left(\alpha_{6} \beta_{6}\right)\) organization. The \(\alpha\) -subunits bind aspartate and are considered catalytic subunits, whereas the \(\beta\) -subunits bind CTP or ATP and are considered regulatory subunits. How would you describe the subunit organization of ATCase from a functional point of view?

Write a balanced equation for the conversion of aspartate to fumarate by the purine nucleoside cycle in skeletal muscle.
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