In DNA: OC is a purine OC pairs with T OT is a purine A pairs with T OA is a purine OG pairs with A OG pairs with C G is a purine
Check all of the following that are components of a SINGLE nucleotide A repeating sugar phosphate backbone A deoxyribose sugar
A. A double helix A3′ OH
B. A nitrogenous base A ribose sugar A5′ phosphate group
C. Complimentary base-pairing
Check all of the following that apply to the secondary structure of DNA:
A. Complimentary base pair holds strands together
B. Parallel polynucleotide strands
C. Nitrogenous bases make up the backbone or sides of the ladder
D. Nitrogenous bases make up the rungs of the ladder
E. Antiparallel polynucleotide strands
A pairs with G A repeating ribose deoxyribose backbone
A repeating sugar phosphate backbone
The Correct Answer and Explanation is:
Let’s address each part of your question by separating the components:
Part 1: DNA Statements – Identify the correct ones
✅ A pairs with T
✅ A is a purine
✅ G is a purine
❌ OC is a purine → No such base “OC”
❌ OC pairs with T → Invalid pairing
❌ OT is a purine → No such base “OT”
❌ OG pairs with A → G (guanine) pairs with C, not A
✅ OG pairs with C → G pairs with C correctly
Part 2: Components of a Single Nucleotide – Check all that apply
✅ A deoxyribose sugar
✅ A 3′ OH
✅ A nitrogenous base
✅ A 5′ phosphate group
❌ A ribose sugar → Found in RNA, not DNA
❌ A repeating sugar phosphate backbone → This is a feature of the DNA strand, not a single nucleotide
❌ A double helix → Refers to the entire DNA structure
❌ Complimentary base-pairing → Refers to DNA strands, not individual nucleotides
Part 3: Features of DNA’s Secondary Structure – Check all that apply
✅ Complimentary base pair holds strands together
❌ Parallel polynucleotide strands → DNA strands are antiparallel, not parallel
❌ Nitrogenous bases make up the backbone or sides of the ladder → Bases form the rungs, not the sides
✅ Nitrogenous bases make up the rungs of the ladder
✅ Antiparallel polynucleotide strands
❌ A pairs with G → Incorrect, A pairs with T
❌ A repeating ribose deoxyribose backbone → Incorrect phrasing
✅ A repeating sugar phosphate backbone
300-Word Explanation
DNA (deoxyribonucleic acid) is a double-stranded molecule composed of nucleotides, each made of three key parts: a deoxyribose sugar, a phosphate group, and a nitrogenous base. These bases are adenine (A), thymine (T), cytosine (C), and guanine (G). The bases are categorized into two types: purines (A and G) and pyrimidines (T and C). Purines are larger, double-ring structures, whereas pyrimidines are smaller, single-ring structures. In DNA, A pairs with T via two hydrogen bonds, and G pairs with C via three hydrogen bonds. These specific pairings ensure the stability of the DNA double helix.
A single nucleotide contains one base (A, T, C, or G), a deoxyribose sugar, a 5′ phosphate group, and a 3′ hydroxyl (OH) group. These nucleotides link together via phosphodiester bonds to form a sugar-phosphate backbone, which is the structural framework of DNA strands. However, this repeating backbone characterizes the entire DNA strand, not individual nucleotides.
The secondary structure of DNA refers to its famous double-helix shape. Two strands of DNA run in antiparallel directions (one 5′ to 3′, the other 3′ to 5′), and are held together by complementary base pairing: A with T, and G with C. The sugar-phosphate backbone forms the sides of the ladder, while the nitrogenous bases form the rungs. This structure allows DNA to be tightly packed and efficiently replicated.
Understanding the distinctions between nucleotide structure and DNA’s overall structure is essential for grasping how genetic information is stored, replicated, and transcribed.