Nucleic acids Knowledge-Based Practice

Questions

1. 1.

   Which chemical factor explains why ribonucleic acid (RNA) undergoes rapid degradation under alkaline conditions, whereas deoxyribonucleic acid (DNA) is resistant?

   • A) The basic medium deprotonates uracil rings, generating electrostatic repulsions that dissociate the backbone.
   • B) The phosphodiester linkages in RNA possess lower intrinsic resonance stabilization than those in DNA.
   • C) The N-glycosidic bonds linking ribose to the nitrogenous bases undergo base-catalyzed hydrolysis.
   • D) The 2'-hydroxyl group of ribose acts as an intramolecular nucleophile that attacks the adjacent phosphodiester bridge.
2. 2.

   In the chemical structure of a nucleoside or nucleotide, which type of covalent linkage connects the nitrogenous base to the pentose sugar unit?

   • A) A $\beta$-N-glycosidic bond between the C1' carbon of the pentose and a nitrogen atom of the base
   • B) A phosphoester bond between the C5' carbon of the pentose and an exocyclic amino nitrogen of the base
   • C) An $\alpha$-O-glycosidic bond between the C2' carbon of the pentose and an oxygen atom of the base
   • D) An amide linkage between the C3' carbon of the pentose and a ring carbonyl group of the base
3. 3.

   Which of the following nitrogenous bases possesses a bicyclic purine ring system and forms three hydrogen bonds with its complementary base in double-stranded DNA?

   • A) Cytosine
   • B) Thymine
   • C) Guanine
   • D) Uracil
4. 4.

   In nucleic acid chemistry, which structural feature distinguishes the pentose sugar unit of ribonucleic acid (RNA) from that of deoxyribonucleic acid (DNA)?

   • A) The attachment of an extra hydroxyl group at the 1' position
   • B) The absence of the primary alcohol group at the 5' position
   • C) The loss of the secondary hydroxyl group at the 3' position
   • D) The presence of a hydroxyl group at the 2' position instead of a hydrogen atom
5. 5.

   Which of the following describes the repeating covalent linkage that joins individual nucleotide monomers together in the backbone of a nucleic acid chain?

   • A) An amide bond connecting an amino group on one nitrogenous base to a carboxyl group on an adjacent base
   • B) An N-glycosidic bond linking carbon-1 of one pentose sugar directly to carbon-4 of the neighboring pentose ring
   • C) A phosphodiester bond connecting the 3'-carbon of one pentose sugar to the 5'-carbon of the adjacent sugar via a phosphate group
   • D) An ether linkage formed by the condensation of hydroxyl groups at the 2'-positions of adjacent ribonucleotide units

Answers and step-by-step solutions appear after you finish the test.