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Nucleotide Metabolism: Delving into the Synthesis and Breakdown of Nucleotides

Description: Welcome to the quiz on Nucleotide Metabolism: Delving into the Synthesis and Breakdown of Nucleotides. Test your understanding of the fundamental processes involved in nucleotide synthesis and breakdown, including the key enzymes, pathways, and their regulation.
Number of Questions: 15
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Tags: biochemistry nucleotides nucleotide metabolism synthesis breakdown
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Which enzyme is responsible for the de novo synthesis of purine nucleotides?

  1. Phosphoribosyl pyrophosphate amidotransferase

  2. Glutamine phosphoribosyl pyrophosphate amidotransferase

  3. Inosine monophosphate dehydrogenase

  4. Ribose-5-phosphate isomerase


Correct Option: B
Explanation:

Glutamine phosphoribosyl pyrophosphate amidotransferase (GPAT) catalyzes the first step in the de novo synthesis of purine nucleotides, where glutamine donates an amino group to phosphoribosyl pyrophosphate (PRPP) to form 5-phosphoribosylamine.

What is the precursor for the synthesis of pyrimidine nucleotides?

  1. Orotic acid

  2. Uracil

  3. Cytosine

  4. Thymine


Correct Option: A
Explanation:

Orotic acid is the precursor for the synthesis of pyrimidine nucleotides. It is formed from carbamoyl phosphate and aspartate in the cytoplasm and then transported into the nucleus for further reactions.

Which enzyme catalyzes the conversion of orotic acid to uridine monophosphate (UMP)?

  1. Orotidine 5'-phosphate decarboxylase

  2. Uridine kinase

  3. Cytidine kinase

  4. Thymidine kinase


Correct Option: A
Explanation:

Orotidine 5'-phosphate decarboxylase catalyzes the decarboxylation of orotic acid 5'-phosphate (OMP) to form UMP, which is the first committed step in the de novo synthesis of pyrimidine nucleotides.

What is the role of ribonucleotide reductase in nucleotide metabolism?

  1. De novo synthesis of nucleotides

  2. Breakdown of nucleotides

  3. Conversion of ribonucleotides to deoxyribonucleotides

  4. Regulation of nucleotide pools


Correct Option: C
Explanation:

Ribonucleotide reductase catalyzes the conversion of ribonucleotides to deoxyribonucleotides, which are essential for DNA synthesis and repair.

Which enzyme is responsible for the salvage pathway of nucleotide synthesis?

  1. Phosphoribosyl pyrophosphate amidotransferase

  2. Glutamine phosphoribosyl pyrophosphate amidotransferase

  3. Hypoxanthine-guanine phosphoribosyltransferase

  4. Thymidine kinase


Correct Option: C
Explanation:

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is a key enzyme in the salvage pathway of nucleotide synthesis, where it catalyzes the transfer of a phosphoribosyl group from PRPP to hypoxanthine or guanine to form IMP or GMP, respectively.

What is the end product of purine catabolism?

  1. Uric acid

  2. Allantoin

  3. Hypoxanthine

  4. Xanthine


Correct Option: A
Explanation:

Purine catabolism ultimately leads to the formation of uric acid, which is the final product of purine degradation in humans and other primates.

Which enzyme catalyzes the conversion of xanthine to uric acid?

  1. Xanthine oxidase

  2. Uricase

  3. Allantoinase

  4. Allantoicase


Correct Option: A
Explanation:

Xanthine oxidase catalyzes the oxidation of xanthine to uric acid, which is the final step in the catabolism of purines.

What is the role of adenosine deaminase in nucleotide metabolism?

  1. De novo synthesis of nucleotides

  2. Breakdown of nucleotides

  3. Conversion of adenosine to inosine

  4. Regulation of nucleotide pools


Correct Option: C
Explanation:

Adenosine deaminase catalyzes the conversion of adenosine to inosine, which is an important step in the breakdown of purine nucleotides.

Which enzyme is responsible for the deamination of cytidine and deoxycytidine?

  1. Cytidine deaminase

  2. Deoxycytidine kinase

  3. Thymidine kinase

  4. Uridine kinase


Correct Option: A
Explanation:

Cytidine deaminase catalyzes the deamination of cytidine and deoxycytidine to form uridine and deoxyuridine, respectively, which are further metabolized in the pyrimidine catabolic pathway.

What is the role of nucleotidases in nucleotide metabolism?

  1. De novo synthesis of nucleotides

  2. Breakdown of nucleotides

  3. Conversion of ribonucleotides to deoxyribonucleotides

  4. Regulation of nucleotide pools


Correct Option: B
Explanation:

Nucleotidases are enzymes that catalyze the hydrolysis of nucleotides into nucleosides and phosphate, thereby playing a crucial role in the breakdown of nucleotides.

Which enzyme is responsible for the hydrolysis of RNA to its constituent nucleotides?

  1. Ribonuclease A

  2. Ribonuclease H

  3. Ribonuclease P

  4. Ribonuclease T


Correct Option: A
Explanation:

Ribonuclease A is an endoribonuclease that catalyzes the hydrolysis of RNA at specific internal phosphodiester bonds, resulting in the release of individual nucleotides.

What is the role of deoxyribonuclease I in nucleotide metabolism?

  1. De novo synthesis of nucleotides

  2. Breakdown of nucleotides

  3. Conversion of ribonucleotides to deoxyribonucleotides

  4. Regulation of nucleotide pools


Correct Option: B
Explanation:

Deoxyribonuclease I is an exonuclease that catalyzes the hydrolysis of DNA from the 3' end, releasing individual nucleotides or small oligonucleotides.

Which enzyme is responsible for the regulation of nucleotide pools?

  1. Phosphoribosyl pyrophosphate amidotransferase

  2. Glutamine phosphoribosyl pyrophosphate amidotransferase

  3. Inosine monophosphate dehydrogenase

  4. Ribose-5-phosphate isomerase


Correct Option: C
Explanation:

Inosine monophosphate dehydrogenase (IMPDH) is a key enzyme in the regulation of nucleotide pools. It catalyzes the conversion of IMP to xanthine monophosphate (XMP), which is a precursor for the synthesis of both purine and pyrimidine nucleotides.

What is the role of feedback inhibition in nucleotide metabolism?

  1. Stimulates the synthesis of nucleotides

  2. Inhibits the synthesis of nucleotides

  3. Converts ribonucleotides to deoxyribonucleotides

  4. Regulates the breakdown of nucleotides


Correct Option: B
Explanation:

Feedback inhibition is a regulatory mechanism in nucleotide metabolism where the end product of a pathway inhibits the activity of an enzyme earlier in the pathway, thereby preventing the overproduction of nucleotides.

Which enzyme is subject to feedback inhibition by GTP and ATP?

  1. Phosphoribosyl pyrophosphate amidotransferase

  2. Glutamine phosphoribosyl pyrophosphate amidotransferase

  3. Inosine monophosphate dehydrogenase

  4. Ribose-5-phosphate isomerase


Correct Option: B
Explanation:

Glutamine phosphoribosyl pyrophosphate amidotransferase (GPAT) is subject to feedback inhibition by GTP and ATP, which are the end products of purine nucleotide synthesis. This feedback mechanism helps to maintain a balance in the nucleotide pools.

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