Summary
Highlights
DNA is a double helix, made of two strands wrapped around each other. Each strand is a polymer composed of smaller units called monomers, which in DNA are called nucleotides.
Each nucleotide consists of three parts: a phosphate, a sugar, and a base. While the phosphate and sugar are identical in all nucleotides, there are four different types of bases: adenine (A), thymine (T), cytosine (C), and guanine (G). This means there are four different types of nucleotides.
Nucleotides link together when the phosphate of one bonds to the sugar of the next, forming a long chain known as the sugar-phosphate backbone. This backbone acts as a protective outer casing for the bases.
The bases extend inwards from the sugar-phosphate backbone and are responsible for holding the two DNA strands together. Complementary base pairing dictates that A always pairs with T, and C always pairs with G. This rule allows us to determine the sequence of a complementary DNA strand.
The genetic code refers to the sequence of bases in DNA. A gene is a specific sequence of bases that codes for a particular protein. Each group of three bases, called a triplet, codes for a specific amino acid.
Cells read the DNA base sequence as a series of triplet codes. The amino acids corresponding to these triplets are then joined together in order, forming a long chain. This chain of amino acids then folds into a unique three-dimensional shape, creating a protein.
The unique sequence and shape of each protein determine its specific function. Proteins perform various vital roles, including acting as enzymes (biological catalysts), hormones (chemical messengers), and structural components that provide strength to cells and tissues.