There is {TAIL ~ no limitation} on the type of other chemical group that can be incorporated on {HEAD ~ the individual nucleotides} 
There is { TAIL ~ no limitation } on the type of other chemical group that can be incorporated on { HEAD ~ the individual nucleotides }
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD