関連ワード:
what is a strand of dna double helix what are the two strands of dna double helix held together by what forms the backbone strands of dna double helix what is responsible for holding the two strands of dna double helix together what two strands of dna form a double helix what is dna double helix how many strands make up a dna double helix why is dna a double helix and rna a single strand
