Question

Write down the salient features of double helix structure of DNA (any three points).

Hint:

Always remember the bond counts: 2 H-bonds for A-T, 3 H-bonds for G-C. This makes G-C regions more stable.

Answer 1

Step 1: Understanding the Concept:
The DNA double helix has specific geometric and chemical properties that allow it to store and replicate genetic information.
Step 2: Detailed Explanation:
Any three of the following salient features can be noted:
1. Anti-parallel Polarity: DNA is made of two polynucleotide chains. If one chain has the polarity \(5' \rightarrow 3'\), the other has \(3' \rightarrow 5'\).
2. Base Pairing: The bases in two strands are paired through hydrogen bonds. Adenine forms two hydrogen bonds with Thymine (\(A=T\)), and Guanine forms three hydrogen bonds with Cytosine (\(G\equiv C\)).
3. Helical Geometry: The two chains are coiled in a right-handed fashion. The pitch of the helix is \(3.4\,\text{nm}\) and there are roughly \(10\,\text{bp}\) in each turn. The distance between base pairs is \(0.34\,\text{nm}\).
4. Backbone: The backbone is constituted by sugar-phosphate, and the bases project inside.
Step 3: Final Answer:
Key features include anti-parallel strands, complementary base pairing via hydrogen bonds, and a right-handed helical structure.