上游充通大兽 1 A Nucleic Acid Consists of 4 Kinds of Bases SHANGHAI JIAO TONG UNIVERSITY Linked to a Sugar-Phosphate Backbone 核酸链的方向：5-向3’- 核酸的碱基序列是核酸的一级结构：5'ACGCTGTA3' base base base OH OH OH 3 OH 5 Figure 4.7 Structure of a DNA chain.The chain has a 5'end,which is usually attached to a phosphate group,and a 3'end,which is usually a free hydroxyl group.Figure 4.7 Structure of a DNA chain. The chain has a 5' end, which is usually attached to a phosphate group, and a 3' end, which is usually a free hydroxyl group. 1 A Nucleic Acid Consists of 4 Kinds of Bases Linked to a Sugar-Phosphate Backbone 核酸链的方向：5’- 向 3’- 核酸的碱基序列是核酸的一级结构：5’ ACGCTGTA 3’