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