# What is palindromic DNA?

What is palindromic DNA and why isn't every complementary strand palindromic?

I know AGCT is palindromic, but what is an example of a strand that isn't?

• I'm voting to close this question as off-topic because it seems to be more about biology than pure chemistry. Better move to Biology.SE
– Jori
Apr 1 '15 at 19:06
• It came from a biochem course. I was eavesdropping in some friends when they were studying. Apr 1 '15 at 19:23
• This is a chemistry question, not a biology question. DNA is a complex heteropolymer and whether or not comething is a palindrome can affect the polymer's reactivity and behavior. Also, since when have questions needed to be about "pure" chemistry to be on topic around here? :-) Apr 1 '15 at 22:31

A palindromic stretch of DNA is a strand whose reverse complement is itself. So 5'-AAAT-3' is not palindromic. It's reverse complement is 5'-ATTT-3'. Those two pieces of DNA are not identical. However, 5'-GGATCC-3' is palindromic, because the reverse complement is identical.

It has nothing to do with the complementarity (of the other strand).

Try this to figure out whether some sequences are palindromic:

#!/usr/bin/env python3
def is_palindromic(seq):
translation_table = str.maketrans('ACGT', 'TGCA')
translation = seq.translate(translation_table)
#print(seq, translation[::-1])
return seq == translation[::-1]

is_palindromic('GATTACA')