As described earlier, {TAIL ~ the nucleotides} can be modified in any number of ways, including modifications of {HEAD ~ the ribose and phosphate and base positions} 
As described earlier , { TAIL ~ the nucleotides } can be modified in any number of ways , including modifications of { HEAD ~ the ribose and phosphate and base positions }
OTH OTH 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 HEAD HEAD HEAD HEAD