Biological Molecules - Structure of DNA

$DNA$ (Deoxyribonucleic acid) is the molecule that contains the genetic instructions for the development, functioning, growth, and reproduction of all known organisms.

The basic unit of $DNA$ is a nucleotide, which consists of three parts: a phosphate group, a pentose sugar (deoxyribose), and a nitrogenous base.

There are four types of nitrogenous bases in $DNA$: Adenine ($A$), Thymine ($T$), Cytosine ($C$), and Guanine ($G$).

The $DNA$ molecule consists of two strands coiled together to form a double helix.

The two strands are held together by hydrogen bonds between complementary base pairs: $A$ always pairs with $T$, and $C$ always pairs with $G$.

The 'backbone' of the $DNA$ strand is formed by alternating sugar and phosphate groups, linked by strong covalent bonds.

The sequence of bases along a $DNA$ molecule forms the genetic code, which determines the specific proteins synthesized by the cell.