CONCEPT OF DIRECTIONALITY
The concept of directionality used in biological systems is useful in describing the conventions to be adopted by the Database Institutions. The rules are:
a) The sequences are always listed in the direction 5' to 3' regardless of the published order.
b) Bases are numbered sequentially beginning with 1 at the 5’ end of the sequence.
c) The complementary sequence is described with a 'c' indicated next to the given strand.
d) Only one strand of the DNA sequence is given in a database entry. The complementary strand will have to be inferred using programs available from websites.
e) Complementary sequence also runs 5'-3' but in the opposite directions to the given strand.
f) In case of proteins, they are synthesized in the cell from N-terminus to the C-terminus.