DNA

DNA size, smallest to biggest:
Nucleotide, DNA, Gene, Chromosome, Genome

Nucleotide
adenine, thymine, guanine, cytosine

DNA
one long molecules spiraling around in a double helix. The helix is made of four smaller molecule by the letters A, T, C, G.

Gene
special sequence of DNA

Genome
defining set of chromosomes that contain all of its genetic information, e.g. human genome, for example, is the set of genetic information encoded in 46 chromosomes found in the nucleus of each cell.