Chapter 25. Chapter 25

Problem-Solving Video Assessment

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Chapter 25 Problem-Solving Video Assessment

Imagine that cells are grown on amino acids that have been labeled with ¹³C within the carboxyl group attached to the α carbon.

1.

Which atom in the uracil base will be labeled with ¹³C? Assume that the nitrogen attached to the ribose sugar is “nitrogen 1” and that numbering moves in a clockwise direction from nitrogen 1.

None of the atoms in the uracil base will be labeled with ¹³C.

carbon 2

carbon 4

carbon 5

carbon 6

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

2.

Which atom(s) in the adenine base will be labeled with ¹³C? Use Figure 25.5 to identify atomic position within the purine ring.

carbon 2

carbon 4

carbon 6

carbon 8

carbons 4 and 6

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

(Questions 3-4) Imagine that you have a system for measuring de novo nucleotide synthesis in vitro. You add all necessary reactants, enzymes, and cofactors to this system. Importantly, you add amino acids that have been uniformly labeled with ¹⁵N.

3.

Which atom(s) in the cytosine base will be labeled with ¹⁵N? Assume that the nitrogen attached to the ribose sugar is “nitrogen 1” and that numbering moves in a clockwise direction from nitrogen 1.

nitrogen 1

nitrogen 3

the nitrogen attached to carbon 4

nitrogen 1 and the nitrogen attached to carbon 4

All of the nitrogen atoms in the cytosine base will be labeled with ¹⁵N.

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

4.

Which atom(s) in the guanine base will be labeled with ¹⁵N? Use Figure 25.5 to identify atomic position within the purine ring.

All nitrogen atoms will be labeled except for the nitrogen attached to carbon 2.

All nitrogen atoms will be labeled except for nitrogen 9.

Only nitrogen 1 will be labeled with ¹⁵N.

Only nitrogen 7 will be labeled with ¹⁵N.

All of the nitrogen atoms in the guanine base will be labeled with ¹⁵N.

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

5.

Which of the following statements comparing the de novo synthesis of pyrimidines to purines is correct?

Only pyrimidine synthesis requires PRPP.

Only purine synthesis requires PRPP.

Amino groups from glutamine can be incorporated into the structure of both pyrimidine and purine bases.

Carbon atoms from aspartate are incorporated into the ring structure of both pyrimidines and purines.

During purine synthesis, free bases are synthesized first and then attached to ribose. In contrast, the pyrimidine ring is built a few atoms at a time, attached to ribose during the entire process.

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

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Chapter 25. Chapter 25

Introduction

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