DNA structure and replication

Nucleotides

Made up of three components: phosphate group, pentose suga and a nitrogenous base.
There are four possible bases: adenine, guanine, cytosine and thymine.
Cytosine and thymine are pyrimadines
Adenime and guanine are purines.
There is a phosphodiester bond between the phosphate group and the pentose sugar.

Polynucleotide

The polynucleotide has a phosphate and sugar back bone.
The nucleotides join in a condensation reaction where a phosphodiester bond forms between the sugar on the first nucleotide and the phosphate group on the next nucleotide.

Double helix formation

DNA has a double helix structure. DNA stands for deoxyribose nucleic acid. A polynucleotide forms in a condensation reaction by the pentode sugar and the next phosphate group joining with a phosphodiester bond. Another polynucleotide runs in the opposite direction (antiparallel). The complementary bases line up and two hydrogen bonds form between A and T, and three hydrogen bonds form between G and C. Because the chains are antiparallel and the bases are different sizes, the chains twist, forming a helix. Thymine and cytosine are pyrimidines, and adenine and guanine are purines.

Replication of DNA

It is a semi conservative process.
DNA polymerase brings bases together and hydrogen bonds form.
DNA ligament sticks the back bone together.
DNA helicase unzips the strand.