Q.16 The bases present in DNA are
(A) adenine, cytosine, guanine and thymine
(B) adenine, guanine, thymine and uracil
(C) adenine, cytosine, thymine and uracil
(D) cytosine, guanine, thymine and uracil
The correct answer is (A) adenine, cytosine, guanine and thymine.
DNA contains these four nitrogenous bases, which form the fundamental units of its double-helix structure.
Option Analysis
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(A) Adenine, cytosine, guanine, thymine: This lists the exact four bases in DNA—A (purine), G (purine), C (pyrimidine), T (pyrimidine)—that pair as A-T (two hydrogen bonds) and G-C (three hydrogen bonds).
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(B) Adenine, guanine, thymine, uracil: Incorrect because uracil replaces thymine in RNA, not DNA; thymine provides DNA’s stability via methylation.
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(C) Adenine, cytosine, thymine, uracil: Wrong as it omits guanine (essential for G-C pairing) and includes uracil, which is RNA-specific.
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(D) Cytosine, guanine, thymine, uracil: Invalid since it excludes adenine and adds uracil, disrupting DNA’s base composition.
The bases present in DNA—adenine, cytosine, guanine, and thymine—form the core of genetic information storage. These nitrogenous bases pair specifically to create DNA’s double helix, vital for replication and protein synthesis in life sciences.
DNA Bases Structure
Adenine (A) and guanine (G) are purines with two rings; cytosine (C) and thymine (T) are pyrimidines with one ring. This ensures uniform helix width. Thymine distinguishes DNA from RNA, where uracil (U) substitutes it.
Base Pairing Rules
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A pairs with T via two hydrogen bonds.
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G pairs with C via three hydrogen bonds.
These pairings maintain genetic fidelity during cell division.
Exam Relevance
For CSIR NET Life Sciences, memorize: DNA bases are A, C, G, T; RNA has A, C, G, U. Common traps include mixing uracil into DNA options.
