Nucleotides are joined together by covalent bonds between the phosphate group of one nucleotide and the third carbon atom of the pentose sugar in the next nucleotide. This produces an alternating backbone of sugar – phosphate – sugar – phosphate all along the polynucleotide chain.

Genetic information is carried in the linear sequence of nucleotides in DNA. Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds between G-C and A-T base pairs.

Nucleic acids consist of chains of small molecules called nucleotides, which are held together by covalent bonds.

The nucleotides forming each DNA strand are connected by noncovalent bonds, called hydrogen bonds. This selective binding is called complementary base pairing, and creates consistency in the nucleotide sequences of the two DNA polymers that join together to make a chromosome.

The two strands of DNA in a double helix are held together by pairing between the nitrogenous bases in the nucleotides of each strand. In this way, the two DNA strands are stuck together by hydrogen bonds all along their length, forming the “steps” of the spiral staircase that is the double helix.

A molecule of DNA has two strands, composed of nucleotides, that form a double helix shape.

Restriction enzymes (originally isolated from bacteria) cut double-stranded DNA at particular nucleotide sequences into fragments, usually four, five, or six nucleotides long. A restriction enzyme will cleave the DNA wherever the particular recognition sequence (or restriction site) of the enzyme occurs.

Scientists use restriction enzymes to cut DNA into smaller pieces so they can analyze and manipulate DNA more easily. The enzymes that make staggered cuts leave small pieces of single-stranded DNA at the ends of the fragments they cut.