Every living organism contains DNA and thus also nucleotides. When we eat plants or animal's we get nucleotides from them. Our body makes nucleotides and we also re-use nucleotides from dying cells and tissue. The latter is called the salvage pathway. 

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Nucleotides are the smallest units that make up our genetic material - also called DNA and RNA. 

From 3 to 6 billion nucleotides per cell. 

There are 5 nucleotides in total. A for adenine, adenine, cytosine (C), guanine (G), thymine (T), and uracil (U). They function as the basic building blocks of the genetic code, with the bases A, G, C, and T being found in DNA while A, G, C, and U are found in RNA.