Question

The polynucleotide chains in DNA are –
A. Semiconservative
B. Parallel
C. Discontinuous
D. Antiparallel

Answer 1

Hint:DNA strands run opposite in direction to each other. The DNA is made up of deoxyribonucleotides linked to each other by phosphodiester linkages. One strand runs from 3' to 5' and the other runs from 5' to 3'.

Complete answer: DNA stands for Deoxy – ribonucleic acid. This is the genetic material in the majority of the organisms. It is present as a chain of consecutively attached molecules of deoxy – NTPs which are attached to each other via phosphodiester bonds. One strand of DNA is linked to the other strand via hydrogen bonds. These hydrogen bonds hold the two strands close to each other. The number of hydrogen bonds between Adenine and Thymine is 2 while that between Guanine and Cytosine is 3.
The two strands of DNA are called Template strand and Coding Strand. They both run anti-parallel to each other. This means that one strand runs from the 5’ to 3’ direction while the other strand runs from the 3’ to 5’ direction.

So, the answer is option D, i.e., they are anti-parallel to each other.

Additional information:
The replication of DNA is called semi-conservative and semi discontinuous replication.
Semi conservative means that at each step of replication, the new DNA molecule has one parent strand and one new strand.
Semi discontinuous means that one strand of DNA is synthesized without a break while the other strand is synthesized in fragments and then the fragments are stitched together.

Note: The DNA strands run in opposite directions and are parallel to each other. So, they are called anti-parallel. This knowledge also helps in studying DNA replication.