DNA is constructed in an antiparallel manner. This means if you number each of the 5 carbons in the sugar deoxyribose the 3rd carbon will be connected to one phosphate group and the 5th carbon will be attached to another phosphate group of another nucleotide. One strand will go from the 5th carbon atom to the 3rd carbon atom in one direction(5’ -3’). and the complementary strand will go in the direction of the 3rd carbon to the 5th carbon in the same direction(3’-5’). Essentially they are made in opposite directions. If I tell you the nucleotide base sequence of one strand is ACGGACTA.

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    $\begingroup$ I'm not clear what you are asking. If you are asking about convention, convention is to write sequences 5' to 3' (biology.stackexchange.com/questions/71530/…). If you are asking "which strand is the 5'-3' strand" the answer is both and neither: it would be like asking which side of a street is the forward side, they are both forward sides and reverse sides, it depends which direction you are traveling. Can you clarify your question? $\endgroup$
    – Bryan Krause
    Mar 6 '19 at 23:10
  • $\begingroup$ Are you asking whether there is a convention for writing polynucleotide sequences? If so, the answer is yes, 5’ to 3’. But you might have researched that yourself. $\endgroup$
    – David
    Mar 6 '19 at 23:39
  • $\begingroup$ Good analogy, @Bryan. $\endgroup$ Mar 7 '19 at 2:26

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