Antiparallel strands in DNA is due to

Options

A. Disulphide linkage
B. Hydrogen bond
C. Phosphodiester bond
D. Glycosidic bond

Answer

**Step-by-Step Solution:**

1. **Understanding DNA Structure**: DNA is composed of two strands that form a double helix. Each strand is made up of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base.

2. **Identifying the Ends of DNA Strands**: Each DNA strand has a directionality, which is indicated by the 5' (five-prime) and 3' (three-prime) ends. The 5' end has a phosphate group attached to the fifth carbon of the sugar, while the 3' end has a hydroxyl group attached to the third carbon of the sugar.

3. **Antiparallel Orientation**: In the double helix structure, one strand runs in the 5' to 3' direction, while the other strand runs in the 3' to 5' direction. This orientation is referred to as "antiparallel."

4. **Role of Phosphodiester Bonds**: The strands are held together by phosphodiester bonds, which link the sugar of one nucleotide to the phosphate group of the next nucleotide. This bonding creates the backbone of the DNA strand and establishes the directionality of the strands.

5. **Hydrogen Bonds Between Strands**: The two strands are held together by hydrogen bonds between complementary nitrogenous bases (adenine with thymine, and guanine with cytosine). This bonding occurs between the bases of the two antiparallel strands.

6. **Conclusion**: The antiparallel nature of DNA strands is due to the orientation of the phosphodiester bonds and the inherent directionality of the nucleotides, resulting in one strand running 5' to 3' and the other running 3' to 5'.

**Final Answer**: The antiparallel strands in DNA are due to the orientation of the phosphodiester bonds and the directionality of the nucleotides.

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