The two chains of DNA occur side by side in a:
Correct answer: D. Antiparallel and spirally twisted
- A. Straight direction
- B. Parallel but straight
- C. Antiparallel and straight
- D. Antiparallel and spirally twisted
Explanation
DNA is a double helix formed by two strands of nucleotides. These strands run in opposite directions (antiparallel) and are twisted around each other, creating a spiral structure. This configuration allows for the stability and functionality of DNA as it holds genetic information. The correct option highlights these key characteristics: antiparallel orientation and a spiral twist. Other options incorrectly describe DNA as straight or simply parallel, which does not match the known helical structure.
This question appeared on the ETEA MDCAT 2013 paper, which you can sit online with every answer explained.
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About Structure of DNA
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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