crossorigin="anonymous">Why are DNA strands antiparallel - Questions House

Why are DNA strands antiparallel

DNA full form

Full form of DNA is Deoxyribonucleic acid and Full form of RNA is Ribonucleic acid. Both DNA and RNA are nucleic acids present in cells. Now, lets come to our question why are DNA strands antiparallel ?

What are antiparallel strands?

Anti-parallel DNA strands means strands run in opposite directions. DNA strands run parallel to each other but they have opposite alignments.

A single DNA strand has two ends. One end has 5’-P group, where a free phosphate group is attached to deoxyribose sugar. Another end has 3’-OH group, where a free hydroxyl group is attached to a deoxyribose sugar.

The arrangement in DNA chains never has two 5’ (five prime) or 3’ (three prime) at one end. This arrangement is called the antiparallel arrangement. These strands run in opposite directions to each other where the head of one strand is laid against the tail of the other strand of DNA.

DNA strands are antiparallel because of H-bonds

Two of the bases are purines, which are adenine and guanine. Pyrimidines bases are thymine and cytosine. These bases are held together by hydrogen bonds. They are formed by complementary pairs of nitrogen bases — Adenine pair with thymine by two hydrogen bonds. Guanine pair with Cytosine by three hydrogen bonds. This is known as the “Base-Pair Rule“. In a double stranded DNA, because of this base pairing , an adenine always pair with thymine and a guanine always pair with cytosine. This is called complementarity of DNA.

DNA strands antiparallel

Nucleotide Strands:

Each DNA molecule has two nucleotide strands that have a sugar-phosphate backbone, but sugar molecule orientation is opposite in both strands. DNA double helix is in opposite directions because of the opposite orientation of the sugar molecule in them.

This antiparallel arrangement allows base pairs to complement one another. Therefore, antiparallel DNA is structurally more stable than parallel DNA. Anti-parallel stands allow the formation of hydrogen bonds. The antiparallel arrangement of DNA plays an important in DNA replication as it replicates the leading strand one way and the lagging strand the other.


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