In Sanger's method of DNA sequencing, dideoxynucleotides terminate the elongation of DNA during replication. This is because the 3` carbon of dideoxynucleotides:
Correct answer: A. Lack a hydroxyl group
- A. Lack a hydroxyl group
- B. Lack a hydrogen group
- C. Have a nitrogenous base
- D. Have a phosphate group
Explanation
The correct answer is that dideoxy nucleotides lack a hydroxyl group at the 3 carbon. In DNA replication, the 3` hydroxyl group of one nucleotide forms a phosphodiester bond with the 5` phosphate group of the next nucleotide, allowing the chain to elongate. Dideoxy nucleotides, missing this 3` hydroxyl group, prevent the formation of this bond, thus terminating DNA synthesis.The other options are incorrect for the following reasons: Lacking a hydrogen group does not impact the termination process; having a nitrogenous base is a common feature of all nucleotides and does not relate to chain termination; having a phosphate group is necessary but is not the feature that causes termination in dideoxy nucleotides.
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DNA structure includes nucleotides made of deoxyribose, phosphate and nitrogenous bases, arranged in two antiparallel polynucleotide strands. Questions cover the double helix, phosphodiester and hydrogen bonds, complementary base pairing between adenine and thymine and between guanine and cytosine, and the significance of major and minor grooves.
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