All flashcards
Flashcard 1: Which bond forms the nucleic acid sugar-phosphate backbone?
Answer: 3′-5′ phosphodiester bond. Phosphodiester bonds link nucleotides, creating the directional backbone of DNA and RNA.
Flashcard 2: Which functional groups are joined to form a 3′-5′ phosphodiester bond?
Answer: 3′-OH of one sugar to 5′ phosphate of the next nucleotide. This linkage ensures the 5' to 3' polarity in nucleic acid strands.
Flashcard 3: Which bases are pyrimidines in nucleic acids?
Answer: Cytosine, thymine, and uracil. Pyrimidines are single-ringed bases that pair with purines in nucleic acid duplexes.
Flashcard 4: What base is found in RNA but not in DNA?
Answer: Uracil. RNA uses uracil instead of thymine to pair with adenine during transcription and translation.
Flashcard 5: How many hydrogen bonds are in a G-C base pair in DNA?
Answer: 3 hydrogen bonds. Three hydrogen bonds between guanine and cytosine provide stronger pairing in DNA.
Flashcard 6: What is the chemical difference between ribose and deoxyribose?
Answer: Deoxyribose has H at 2′; ribose has OH at 2′. The absence of the 2'-OH in deoxyribose enhances DNA stability by preventing hydrolysis.
Flashcard 7: Which atoms are connected by the N-glycosidic bond in nucleotides?
Answer: Sugar 1′ carbon to base N (purine N9, pyrimidine N1). The glycosidic bond connects the anomeric carbon of the sugar to the nitrogen of the base.
Flashcard 8: What is the standard base-pairing rule in DNA?
Answer: A pairs with T; G pairs with C. Complementary base pairing via hydrogen bonds stabilizes the DNA double helix.
Flashcard 9: What is the standard base-pairing rule in RNA?
Answer: A pairs with U; G pairs with C. RNA uses uracil to pair with adenine, enabling specific interactions in RNA structures.
Flashcard 10: How many hydrogen bonds are in an A-T base pair in DNA?
Answer: 2 hydrogen bonds. Two hydrogen bonds form between adenine and thymine, contributing to DNA stability.
Flashcard 11: Which bases are purines in nucleic acids?
Answer: Adenine and guanine. Purines are double-ringed bases essential for DNA and RNA structure and function.
Flashcard 12: What is the structural difference between a nucleoside and a nucleotide?
Answer: Nucleoside lacks phosphate; nucleotide includes phosphate. Nucleosides are precursors to nucleotides, with the phosphate addition enabling polymerization into nucleic acids.
Flashcard 13: What are the three components of a nucleotide?
Answer: Nitrogenous base + pentose sugar + phosphate group. Nucleotides form the building blocks of nucleic acids, combining these components via covalent bonds.
Flashcard 14: Which end of a nucleic acid strand typically has the free hydroxyl group?
Answer: The 3′ end. The 3' end hydroxyl is the site for chain elongation during nucleic acid synthesis.
Flashcard 15: Which end of a nucleic acid strand typically has the free phosphate group?
Answer: The 5′ end. The 5' end phosphate is where synthesis begins and caps or modifications often occur.
Flashcard 16: Which DNA base pair is expected to increase duplex melting temperature (Tm)?
Answer: Higher G-C content. G-C pairs form three hydrogen bonds, increasing stability and thus raising the melting temperature.
Flashcard 17: What is the major chemical reason RNA is less stable than DNA in base?
Answer: RNA has a 2′-OH that promotes backbone hydrolysis. The 2'-OH in RNA enables nucleophilic attack on the phosphodiester bond in alkaline conditions.
Flashcard 18: Which nitrogenous bases are aromatic and therefore absorb UV light near 260nm?
Answer: All nucleobases (purines and pyrimidines) are aromatic. Aromaticity confers planarity and UV absorbance, useful for quantifying nucleic acids.
Flashcard 19: What is the key structural difference between purines and pyrimidines?
Answer: Purines have two rings; pyrimidines have one ring. The ring structure affects base pairing and stacking interactions in nucleic acids.
Flashcard 20: What base is found in DNA but not in RNA?
Answer: Thymine. DNA incorporates thymine for greater stability against cytosine deamination compared to uracil.