Looking for classes? Ksquare Career Institute, Bengaluru →
Antiparallel strands of a DNA molecule means that -
A
One strand turns anti-clockwise
B
The phosphate groups of two DNA strands, at their ends, share the same position
C
The phosphate groups at the start of two DNA strands are in opposite position (pole)
D
One strand turns clockwise
Detailed Solution
Each polynucleotide strand of DNA has a polarity: one end has a free phosphate group on the $5'$ carbon of the sugar ($5'$ end) and the other end has a free hydroxyl group on the $3'$ carbon ($3'$ end).
In the double helix the two strands run in opposite directions: one runs $5' \rightarrow 3'$ and the other runs $3' \rightarrow 5'$.
So at any one end of the molecule, one strand has its $5'$ phosphate end and the other has its $3'$ hydroxyl end.
In other words, the phosphate groups at the start of the two strands lie at opposite poles of the molecule. This is what antiparallel means.
Both strands are coiled in the same right-handed direction, so it has nothing to do with one strand turning clockwise or anti-clockwise.
So antiparallel means that the phosphate groups at the start of the two DNA strands are in opposite positions (poles).
In the double helix the two strands run in opposite directions: one runs $5' \rightarrow 3'$ and the other runs $3' \rightarrow 5'$.
So at any one end of the molecule, one strand has its $5'$ phosphate end and the other has its $3'$ hydroxyl end.
In other words, the phosphate groups at the start of the two strands lie at opposite poles of the molecule. This is what antiparallel means.
Both strands are coiled in the same right-handed direction, so it has nothing to do with one strand turning clockwise or anti-clockwise.
So antiparallel means that the phosphate groups at the start of the two DNA strands are in opposite positions (poles).