Question

DNA is a double stranded structure, where the strands are said to be anti-parallel. Select the statements that suits the above property of DNA. (i) Length of one gyre is 34 cm. (ii) In DNA strands the phosphate group is in 3' position and OH is in 5' position. (iii) The free ends on both the strands have OH group. (iv) Both strands run parallel but opposite in direction. (A) Only (i) (B) Only (ii) (C) (iii) and (iv) (D) (i), (iii) and (iv)​

Answer 1

The statements that accurately reflect the anti-parallel nature of DNA are (ii) and (iv). Statement (i) is incorrect and (iii) is partially incorrect because only the 3' end of a DNA strand has a free hydroxyl group.

Step-by-step explanation:

The statements that correctly depict the anti-parallel nature of DNA are (ii) and (iv). The term 'anti-parallel' in the context of DNA refers to the fact that the two strands run in opposite directions. Statement (ii) correctly identifies that the phosphate group is at the 3' position and OH group at the 5' position on the sugar-phosphate backbone of a DNA strand. Statement (iv) also correctly identifies that the two strands run parallel but opposite in direction, which is the definition of 'anti-parallel'.

Statement (i) is incorrect because the length of one gyre (a full twist in the DNA double helix) is not 34 cm, but 34 angstroms (or 3.4 nanometers). Statement (iii) is partially correct; while it is true that the 3' end of a DNA strand has a free hydroxyl group, it is not the case that both ends have a hydroxyl group. The 5' end actually has a free phosphate group.

In conclusion, option (C) (iii) and (iv) would be the most accurate choice considering the correct understanding of anti-parallelism and the presence of a free hydroxyl group at one end, though it's worth noting that it's not strictly 100% correct due to the incorrect assertion that both ends have a hydroxyl group.

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