I/GCSE Biology Question Analysis Topic: Biology - DNA
Exam Question:
List the salient features of double helix structure of DNA.
Answer:
For I/GCSE Biology, you should know:
The following are the key characteristics of DNA's double helix structure:
1) A double stranded DNA molecule consists of two polynucleotide chains.
2) The substance that makes up the backbone is called the sugar phosphate.
In other words, one chain has polarity 5'-3' and the other 3'-5', indicating that the two strands have anti-parallel polarity.
3) Purines and pyrimidines form hydrogen bonds that bind the two DNA strands together.
4) Guanine and cytosine are paired with adenine and thymine by three and two pairs of hydrogen bonds respectively.
5) The distance between two base pairs is 3.4 A° and the pitch of the helix is 3.4 nm in the two chains, same like in B-DNA.
6) The sugars and phosphates that make up the DNA double helix's backbone are located where bases are pointing inward.
Work hard for your I/GCSE Biology examination!
End of analysis. Great!
