One bond is not enough 7.3 tRNA contains modified bases that H influence its pairing properties Sugar H Thiouracil h N N Guanine Sugar Figure 7. 8 2-thiouracil pairs only w ith A Modification to 2 CH3 thiouridine restricts pairing to a alone because only one H- ond can form with g Sugar H Thiouracil H Adenine 消当 SugarFigure 7.8 Modification to 2- thiouridine restricts pairing to A alone because only one H￾bond can form with G. 7.3 tRNA contains modified bases that influence its pairing properties