Sticky end/blunt end

Sticky end and blunt end are biological jargon describing the two possible configurations that may result from the breaking of double stranded DNA. DNA exhibits a stabilizing interaction between complementary base pairs, providing specificity to the pairing of two strands of DNA. If two complementary strands of DNA are of equal length, then they will terminate in a blunt end, as in the following example:

5'-CpTpGpApTpCpTpGpApCpTpGpApTpGpCpGpTpApTpGpCpTpApGpT-3'
3'-GpApCpTpApGpApCpTpGpApCpTpApCpGpCpApTpApCpGpApTpCpA-5'

However, if one strand extends beyond the complementary region, then the DNA is said to possess an overhang:

5'-ApTpCpTpGpApCpT-3'
3'-TpApGpApCpTpGpApCpTpApCpG-5'

If another DNA fragment exists with a complementary overhang, then these two overhangs will tend to associate with each other and each strand is said to possess a sticky end:

5'-ApTpCpTpGpApCpT        GpApTpGpCpGpTpApTpGpCpT-3'
3'-TpApGpApCpTpGpApCpTpApCpG        CpApTpApCpGpA-5'
becomes
5'-ApTpCpTpGpApCpT GpApTpGpCpGpTpApTpGpCpT-3'
3'-TpApGpApCpTpGpApCpTpApCpG CpApTpApCpGpA-5'

The two fragments may then be covalently bonded by DNA ligase. Blunt ends may be ligated together, but the reaction is significantly slower. These terms are most commonly used to describe the product of a restriction enzyme digestion of DNA.