When the DNA molecule is inactive, the bases are linked by these hydrogen bonds and the molecule is in its spiral-shaped state.
Nucleic Acid Structure
Nucleotides can be linked together by covalent bonds between the phosphate of one nucleotide and the sugar of next. These linked monomers become the phosphate-sugar backbone of nucleic acids. The nitrogenous bases extend out from this phosphate-sugar backbone like teeth of a comb.
When bases pair up between the two DNA strands, a purine always pairs with a pyrimidine. Specifically adenine (A) and thymine (T) pair up, and cytosine (C) and guanine (G) pair up. These bases are attracted to each other through hydrogen bonding.
When DNA is being used—either being copied (a process called
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