Question 1

Aspartate contains four carbons. If all are radioactively labeled, how many carbons of UMP will be radioactively labeled?
A) 0
B) 2
C) 3
D) 4

Accepted Answer

Aspartate is one of the precursors of UMP (uridine monophosphate). Aspartate has four carbon atoms, and if all of them are radioactively labeled, then three of those carbons will contribute to the formation of carbons in UMP. The fourth carbon will not be incorporated into UMP because it is used to form fumarate, another molecule in the pyrimidine synthesis pathway. Therefore, the correct answer is choice C) 3.

Question 2

Which of the following is an intermediate in the conversion of AMP to uric acid but NOT an intermediate in the conversion of GMP to uric acid? 
A) A
B) B
C) C
D) D

Accepted Answer

The answer of Which of the following is an intermediate...

Question 3

The possibility of ADA-SCID is indicated by than normal activity of .
A) lower; ribonucleotide reductase
B) higher; adenosine deaminase
C) lower; HGPRT
D) higher; xanthine oxidase

Accepted Answer

The answer of The possibility of ADA-SCID is indicated by...

Question 4

During the biosynthesis of UMP from carbamoyl phosphate and aspartate, dihydroorotate is converted to which of the following compounds? A) carbamoyl aspartate B) orotate C) orotidine-5 ^' -monophosphate D) quinone

Accepted Answer

Dihydroorotate is converted to orotate during the biosynthesis of UMP.

Question 5

A person is carrying out in vitro synthesis of uric acid from GMP. He or she wants to include all substrates and enzymes necessary. All EXCEPT should be included in the reaction mixture.
A) adenosine deaminase
B) purine nucleoside phosphorylase
C) guanine deaminase
D) xanthine oxidase

Accepted Answer

Adenosine deaminase is not necessary for the synthesis of uric acid from GMP. The other enzymes listed (purine nucleoside phosphorylase, guanine deaminase, and xanthine oxidase) are all necessary for the complete conversion of GMP to uric acid.

Question 6

If GMP radiolabeled at the nitrogen atom indicated by the * were metabolized to uric acid, which of the following molecules along the pathway would also be radioactive? A) uric acid B) guanine C) NH₄⁺ D) xanthine

Accepted Answer

The answer of If GMP radiolabeled at the nitrogen atom...

Question 7

Uric acid is processed to allantoic acid, which is then secreted. In which of the following organisms does this occur?
A) insects
B) bony fish
C) marine invertebrates
D) amphibians

Accepted Answer

The answer of Uric acid is processed to allantoic acid,...

Question 8

Samples from a bird, reptile, amphibian, and primate were analyzed by Western blotting for the expression of allantoinase, the enzyme that converts allantoin to allantoic acid. Unfortunately the researcher forgot the order that the samples were loaded into the gel. Luckily, only a single sample indicated allantoinase. Which sample contained allantoinase?
A) bird
B) reptile
C) amphibian
D) primate

Accepted Answer

Amphibians have the enzyme allantoinase, which is involved in the conversion of allantoin to allantoic acid, a step in the uric acid metabolism pathway. Birds, reptiles, and primates typically do not have this enzyme because they either excrete uric acid directly or, in the case of primates, further break down uric acid into allantoin but not beyond that point.

Question 9

How many of the nitrogens in orotidine-5 ^' -monophosphate arise from glutamine? A) 0 B) 1 C) 2 D) 3

Accepted Answer

In the biosynthesis of pyrimidines, the nitrogen in the pyrimidine ring of orotidine monophosphate (OMP) comes from glutamine.

Question 10

Marine invertebrates express enzymes that allow for the conversion of uric acid to NH₄⁺. What is the correct order of the action of enzymes in this pathway? 1. Urate oxidase 2) Allantoicase 3) Urease A) 2; 3; 4; 1 B) 1; 2; 4; 3 C) 3; 4; 2; 1 D) 1; 4; 2; 3

Accepted Answer

The correct order of enzyme action in the conversion of uric acid to ammonia (NH3) and carbon dioxide (CO2) in marine invertebrates is: 1) Urate oxidase, which converts uric acid into allantoin; 4) Allantoinase, which converts allantoin into allantoic acid; 2) Allantoicase, which converts allantoic acid into urea and glyoxylate; and 3) Urease, which converts urea into ammonia and carbon dioxide.

Question 11

The conversion of adenosine to inosine is catalyzed by , which is deficient in .
A) HGPRT; Lesch-Nyhan syndrome
B) adenosine deaminase; ADA-SCID
C) xanthine oxidase; Lesch-Nyhan syndrome
D) purine nucleoside phosphorylase; ADA-SCID

Accepted Answer

The conversion of adenosine to inosine is catalyzed by adenosine deaminase (ADA), which is deficient in ADA-SCID (adenosine deaminase-deficient severe combined immunodeficiency). HGPRT (hypoxanthine-guanine phosphoribosyltransferase) deficiency causes Lesch-Nyhan syndrome, but it does not lead to the conversion of adenosine to inosine. Xanthine oxidase deficiency causes hyperuricemia, but it is not involved in the conversion of adenosine to inosine. Purine nucleoside phosphorylase (PNP) deficiency causes PNP deficiency disease, but it does not lead to the conversion of adenosine to inosine.

Question 12

What enzymatic activity is NOT required during the biosynthesis of UMP from carbamoyl phosphate and aspartate?
A) dehydrogenase
B) decarboxylase
C) phosphoribosyl transferase
D) synthetase

Accepted Answer

The answer of What enzymatic activity is NOT required during...

Question 13

The conversion of hypoxanthine to IMP is catalyzed by , which is deficient in .
A) HGPRT; Lesch-Nyhan syndrome
B) adenosine deaminase; ADA-SCID
C) xanthine oxidase; Lesch-Nyhan syndrome
D) purine nucleoside phosphorylase; ADA-SCID

Accepted Answer

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is the enzyme responsible for the conversion of hypoxanthine to IMP. Deficiency in this enzyme leads to Lesch-Nyhan syndrome, a rare genetic disorder characterized by neurological and behavioral symptoms. Adenosine deaminase (ADA) deficiency leads to ADA-SCID (Severe Combined Immunodeficiency), which is a disorder of the immune system. Xanthine oxidase is involved in a different pathway and is not responsible for the conversion of hypoxanthine to IMP. Purine nucleoside phosphorylase is also involved in a different pathway and its deficiency leads to another type of SCID, not ADA-SCID.

Question 14

An enzyme panel analysis of a patient reveals a lack of , which is an indication of Lesch-Nyhan syndrome.
A) PRPP synthetase
B) adenosine deaminase
C) HGPRT
D) xanthine oxidase

Accepted Answer

The lack of HGPRT (hypoxanthine-guanine phosphoribosyltransferase) is a key feature of Lesch-Nyhan syndrome, an X-linked genetic disorder that results in neurological and behavioral abnormalities, as well as increased levels of uric acid. HGPRT plays a role in the recycling of purines, and its deficiency leads to the accumulation of purine metabolites, including hypoxanthine and guanine, which are converted to uric acid. The other enzymes listed are not directly associated with Lesch-Nyhan syndrome.

Question 15

Which of the following is the precursor of the indicated carbon atom in a pyrimidine ring? 
A) aspartate
B) glycine
C) carbamoyl phosphate
D) orotate

Accepted Answer

The precursor of the indicated carbon atom in a pyrimidine ring is carbamoyl phosphate. Carbamoyl phosphate is synthesized from ammonia and carbon dioxide in the first step of the pyrimidine biosynthetic pathway, and it is ultimately converted into orotic acid, which is the precursor of pyrimidine nucleotides. Aspartate and glycine are involved in the biosynthesis of purine nucleotides, while orotate is derived from carbamoyl phosphate, but it is not the precursor of a specific carbon atom in the pyrimidine ring.

Question 16

Place the steps converting GMP to uric acid in the correct order. 
A. Conversion to guanine
B. Conversion to guanosine
C. Conversion to xanthine
D. Conversion to uric acid
A) A; C; B; D
B) A; B; C; D
C) B; C; A; D
D) B; A; C; D

Accepted Answer

The correct sequence for converting GMP (guanosine monophosphate) to uric acid involves first converting GMP to guanosine, then to guanine, followed by conversion to xanthine, and finally to uric acid. This sequence reflects the enzymatic steps involved in purine metabolism.

Question 17

Which of the following organisms would generate this compound? 
A) nonprimate mammals
B) birds
C) cartilaginous fish
D) primates

Accepted Answer

The answer of Which of the following organisms would generate...

Question 18

If a mutation of the decarboxylase enzyme that functions in the biosynthetic pathway of UMP caused the pathway to halt at that step, which of the following would no longer occur? A) reduction of a quinone B) production of orotidine-5 ^' -monophosphate C) generation of CO₂ D) generation of glutamate

Accepted Answer

The decarboxylase enzyme is responsible for removing a carboxyl group, releasing CO2. If the enzyme is mutated and the pathway halts, CO2 generation would no longer occur.

Question 19

A nitrogen of a pyrimidine ring arises from which amino acid?
A) aspartate
B) asparagine
C) glycine
D) alanine

Accepted Answer

Aspartate contributes to the nitrogen in the pyrimidine ring structure during the biosynthesis of nucleotides.

Question 20

Nonprimate mammals convert uric acid to allantoin. This reaction, catalyzed by urate oxidase, also generates which of the following products? A) H₂O B) H₂O₂ C) O₂ D) NH₄⁺

Accepted Answer

The conversion of uric acid to allantoin by urate oxidase produces hydrogen peroxide (H₂O₂) as a byproduct.

Quiz 18: Nucleotide Metabolism

Aspartate contains four carbons. If all are radioactively labeled, how many carbons of UMP will be radioactively labeled?

Which of the following is an intermediate in the conversion of AMP to uric acid but NOT an intermediate in the conversion of GMP to uric acid?

The possibility of ADA-SCID is indicated by than normal activity of .

During the biosynthesis of UMP from carbamoyl phosphate and aspartate, dihydroorotate is converted to which of the following compounds?

A person is carrying out in vitro synthesis of uric acid from GMP. He or she wants to include all substrates and enzymes necessary. All EXCEPT should be included in the reaction mixture.

If GMP radiolabeled at the nitrogen atom indicated by the * were metabolized to uric acid, which of the following molecules along the pathway would also be radioactive?

Uric acid is processed to allantoic acid, which is then secreted. In which of the following organisms does this occur?

How many of the nitrogens in orotidine-5 ' -monophosphate arise from glutamine?

Marine invertebrates express enzymes that allow for the conversion of uric acid to NH4+. What is the correct order of the action of enzymes in this pathway? 1. Urate oxidase 2) Allantoicase 3) Urease

The conversion of adenosine to inosine is catalyzed by , which is deficient in .

What enzymatic activity is NOT required during the biosynthesis of UMP from carbamoyl phosphate and aspartate?

The conversion of hypoxanthine to IMP is catalyzed by , which is deficient in .

An enzyme panel analysis of a patient reveals a lack of , which is an indication of Lesch-Nyhan syndrome.

Which of the following is the precursor of the indicated carbon atom in a pyrimidine ring?

Place the steps converting GMP to uric acid in the correct order. A. Conversion to guanine B. Conversion to guanosine C. Conversion to xanthine D. Conversion to uric acid

Which of the following organisms would generate this compound?

If a mutation of the decarboxylase enzyme that functions in the biosynthetic pathway of UMP caused the pathway to halt at that step, which of the following would no longer occur?

A nitrogen of a pyrimidine ring arises from which amino acid?

Nonprimate mammals convert uric acid to allantoin. This reaction, catalyzed by urate oxidase, also generates which of the following products?

How many of the nitrogens in orotidine-5 ^' -monophosphate arise from glutamine?

Marine invertebrates express enzymes that allow for the conversion of uric acid to NH₄⁺. What is the correct order of the action of enzymes in this pathway? 1. Urate oxidase 2) Allantoicase 3) Urease