The building block of all lifeforms on earth is the deoxyribonucleic acid . it has the shape of a double helix in which two polynucleotide chains are coiled about each other in a spiral 而组成地球上所有生命的基本单位去氧核糖核酸dna的双螺旋结构也是非对称地存在的，原来自然界中的去氧核糖核酸绝大部分都是右旋的。
4.
The building block of all lifeforms on earth is the deoxyribonucleic acid ( dna ) . it has the shape of a double helix in which two polynucleotide chains are coiled about each other in a spiral 而组成地球上所有生命的基本单位去氧核糖核酸( dna )的双螺旋结构也是非对称地存在的，原来自然界中的去氧核糖核酸绝大部分都是右旋的。
