1.5.1 Nucleotides are the building materials of nucleic acids

Deoxyribonucleic acid (DNA)

Ribonucleic acid (RNA)

Nucleic acids → polymers called polynucleotides → made of monomers called nucleotides

Nucleotide = nucleoside + phosphate group

Nucleoside(核苷) = nitrogen base + sugar

Pyrimidines 嘧啶: Cytosine胞嘧啶 Thymine胸腺嘧啶 Uracil尿嘧啶

Purines嘌呤: Adenine腺嘌呤 Guanine鸟嘌呤

（注：嘌呤>嘧啶）

1.5.2 Phosphodiester bonds join nucleotides to form nucleic acids

Phosphodiester 磷酸(二)酯键

5’ - phosphate group （5撇端）

3’ - hydroxyl group （3撇端）

double helix 双螺旋

antiparallel 反向平行

1.5.3 Cellular DNA takes the form of a double helix

A-T → 2 bonds between