Humans--and all other living organisms--need nucleic acids. The nucleic acids, which include deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA, encode genetic information and allow humans and other organisms to follow their genetic instructions. Nucleic acids also allow you to pass along your genetic information to your offspring.
DNA is the nucleic acid with which most people are familiar. Your cells contain DNA in their nuclei, and the DNA encodes genetic information that your cells use to make the structural and functional proteins that allow them to operate. When you produce new cells, old cells duplicate their genetic information, producing two identical sets of DNA. The cell then splits into two, each daughter cell getting a complete set of the genetic code, explains Dr. Lauralee Sherwood in her book "Human Physiology."
DNA isn't the only nucleic acid; you also depend upon RNA. RNA helps the cell make proteins from DNA, because DNA is sequestered in a cell's nucleus, and the protein-making machinery in a cell is outside the nucleus. RNA transfers genetic information from inside the nucleus to outside, and also helps to read the genetic information and generate protein from it, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Yet another reason you need nucleic acid is so you can reproduce, passing your genetic information on to your children. Your eggs or sperm each contain half of your DNA. When you conceive a child, you combine half your DNA with half of your partner's DNA, producing a fertilized egg with a full set of DNA. This fertilized egg contains all the genetic information necessary to produce a fully functional human.
While you need nucleic acids in your body, you don't need them in your diet. Humans have a very limited ability to take up the building blocks of nucleic acids, called nucleotides, from the digestive tract. Instead, we tend to make our own nucleotides, using amino acids as precursors. Amino acids are the building blocks of proteins. As such, when you consume protein and digest it into amino acids, you're obtaining the building blocks for both proteins and, eventually, nucleic acids.