A palindrome is a sequence of letters and/or words, that reads the same forwards and backwards.
"able was I ere I saw elba" is a palindrome.
Palindromes also occur in DNA.
There are two types.
5' GGCC 3'
3' CCGG 5'
This type of palindrome serves as the target for most restriction enzymes.
The graphic shows the palindromic sequences "seen" by five restriction enzymes (named in blue) commonly used in recombinant DNA work. [Discussion]
In these cases, two different segments of the double helix read the same but in opposite directions.5' AGAACAnnnTGTTCT 3'
Inverted repeats are commonly found in
This graphic shows the "recognition helix" to which the CAP protein (a homodimer) binds in the lac operon of E. coli. [Discussion]
The human Y chromosome contains 7 sets of genes — each set containing from 2 to 6 nearly-identical genes — oriented back-to-back or head-to-head; that is, they are inverted repeats like the portion shown here. (The dashes represent the thousands of base pairs that separate adjacent palindromes.)
5' ...CACAATTCCCATGGGTTGTGGGAG 3' ----------- 5' CTCCCACAACCCATGGGATTTGTG... 3'
3' ...GTGTTAAGGGTACCCAACACCCTC 5' ----------- 3' GAGGGTGTTGGGTACCCTAAACAC... 5'
This orientation and redundancy may help ensure that a deleterious mutation in one copy of the set can be repaired using the information in another copy of that set. All that is needed is to form a loop so that the two sequences line up side-by-side. Repairs can then be made (probably by the mechanism of homologous recombination). Here, for example, the single difference in the sequences can be eliminated (red for blue or vice versa). [More on the Y chromosome]