DNA is made up of four chemical bases: adenine, guanine, cytosine and thymine. These four bases are primarily made up of nitrogen, hydrogen, carbon and oxygen, which are the four most common elements in living things. When forming a DNA molecule, adenine binds with thymine and guanine binds with cytosine. Each individual base is also bound to a sugar molecule or a phosphatase molecule. All the bases and bounded molecules together form a nucleotide.
DNA has the ability to self-replicate; thus, DNA molecules are the builders for new DNA molecules. The process of self-replication is called mitosis, and there are five phases to mitosis. The first phase is interphase, which is when the DNA is coiled up inside a structure called chromosomes; during interphase, DNA copies itself. The second phase is prophase, which involves the chromosomes becoming undone. The third phase is metaphase, in which the duplicate DNA molecules line up next to one another. The fourth phase is anaphase, in which the molecules go to the opposite end of the cell. In the fifth phase, telophase, the cell cleaves and splits in half, with each cell having the exact same DNA.
Prokaryotes are simple, single-celled organisms that are classified in Kingdom Monera (which is most known bacteria) and Kingdom Archaea (which are bacteria that live in extreme circumstances, such as on the bottom of sea vents). The DNA of prokaryotes are nearly identical in function of more complex organisms: it contains the same bases and it replicates through mitosis (though, for a prokaryotes, mitosis is effectively its reproduction since it is a single-celled organism and mitosis makes a new cell). There are no chromosomes in a prokaryote's DNA; instead, a prokaryote's DNA is in a circular shape, as opposed to coils.
Eukaryotes are multi-celled organisms and a handful of single-celled organisms (called protists) that have a more complex cell than prokaryotes; importantly, eukaroytes have a special cell organelle called a nucleus, which is where most of their DNA is stored (though some of it is in an organelle called the mitochondria). Importantly, despite the fact that the individual cells may have different functions in a multi-cellular organism, each cell has the same DNA; certain parts of the DNA are simply non-functioning depending on what the cells needs to do.