Why the distance between two polynucleotide chains in DNA remains constant?

Question

Accepted Answer

Each polynucleotide chain of a double helical DNA structure is attached each other by hydrogen bonding forming specific number of base pairs.

Adenine forms two hydrogen bonds with Thymine from opposite strand and Thymine forms two hydrogen bonds with Adenine.

Similarly, Guanine is bonded with Cytosine with three hydrogen bonds.

As a result of these bonds, the distance between two polynucleotide chains in DNA remains (almost) constant.

Answer

In the DNA double helix,purine always pairs with pyrimidine through H-bond,that lead to uniform width throughout the fragment...

Hope u get it...
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Answer

Due to hydrogen bonding between purine and pyrimidine....

Answer

The Constant Distance Between Two Polynucleotide Chains in DNA

DNA, or deoxyribonucleic acid, is a double-stranded molecule that carries the genetic information in most organisms. The structure of DNA consists of two polynucleotide chains that are arranged in a double helix. The distance between these two chains remains constant due to several factors.

1. Hydrogen Bonding
- The stability of the double helix structure of DNA is primarily maintained by hydrogen bonding between the complementary nitrogenous bases.
- Adenine (A) forms two hydrogen bonds with thymine (T), and guanine (G) forms three hydrogen bonds with cytosine (C).
- These hydrogen bonds occur between the bases on opposite polynucleotide chains, holding them together.

2. Complementary Base Pairing
- The base pairing between the two polynucleotide chains follows a specific pattern: A always pairs with T, and G always pairs with C.
- The complementary base pairing ensures that the distance between the two chains remains constant, as the specific base pairs have a consistent shape and size.

3. Phosphodiester Backbone
- The polynucleotide chains of DNA are composed of nucleotides linked together by phosphodiester bonds.
- The phosphodiester backbone of DNA provides structural stability to the molecule.
- The phosphate groups in the backbone are negatively charged, causing the DNA molecule to have a uniform negative charge along its length.
- This uniform charge distribution helps to repel the negatively charged strands of DNA, maintaining a constant distance between them.

4. Antiparallel Arrangement
- The two polynucleotide chains in DNA are arranged in an antiparallel manner, meaning they run in opposite directions.
- One chain has a 5' end (with a phosphate group) and a 3' end (with a hydroxyl group), while the other chain has a complementary orientation.
- The antiparallel arrangement ensures that the hydrogen bonding and base pairing occur in a consistent manner, leading to a constant distance between the two chains.

Conclusion
The distance between the two polynucleotide chains in DNA remains constant due to the hydrogen bonding between the bases, complementary base pairing, the phosphodiester backbone, and the antiparallel arrangement of the chains. These factors work together to maintain the stability and integrity of the DNA molecule, allowing it to serve as a reliable carrier of genetic information.

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