What is Nucleic Acid?

Nucleic acid is essential for all forms of life, and it is found in all cells. Nucleic acid comes in two natural forms called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

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Nucleic acids are made of biopolymers, which are naturally-occurring, repeated sets of monomers (making polymers) that then create nucleotides, which form nucleic acids.

To understand the structure of nucleic acid, it is important to understand the structure of the nucleotides that make up nucleic acid.

The Structure of Nucleic Acid

A nucleotide is made up of three parts that are attached by bonds. The three parts are a phosphate group, a 5-carbon sugar, and a nitrogen base.

Phosphate group

The phosphate group is made up of a phosphorus atom with four negatively charged oxygen atoms attached to it.

5-carbon sugar

The 5-carbon sugar (known as a pentose) includes ribose and deoxyribose, which are present in nucleic acid. Both ribose and deoxyribose have five carbon atoms and one oxygen atom. Attached to the carbon atoms are hydrogen atoms and hydroxyl groups.

In ribose sugar, there are hydroxyl groups attached to the second and third carbon atoms. In deoxyribose sugar, there is a hydroxyl group attached to the third carbon atom, but only a hydrogen atom is attached to the second carbon atom.

Nitrogen base

The nitrogen molecule acts as a base in nucleic acid because it can give electrons to other molecules and create new molecules through this process. It can bind to carbon, hydrogen, and oxygen molecules to create ring structures.

Ring structures come in single rings (pyrimidines) and double rings (purines). Pyrimidines include thymine, cytosine, and uracil. Purines include adenine and guanine. Purines are larger than pyrimidines, and their size differences help to determine their pairings in DNA strands.

Nucleic acid bonds

The bonds that hold together the phosphorus, sugar, and nitrogen molecules are called glycosidic bonds and ester bonds.

Glycosidic bonds are made between the first carbon atom in a 5-carbon sugar and the ninth nitrogen atom in a nitrogenous base.

Ester bonds are made between the fifth carbon atom in a 5-carbon sugar and the phosphate group.

These bonds not only hold together a single nucleotide, but they also hold together chains of nucleotides that create polynucleotides that form deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

To create these chains, the phosphate group that is bound to the fifth carbon atom in a 5-carbon sugar will bind to the third carbon atom in the next 5-carbon sugar. This will repeat to create a chain held together by a sugar-phosphate backbone.

If the sugar in this chain is a ribose sugar, a strand of RNA will be created.

To create DNA, the RNA strand bonds to a polynucleotide that has a similar but anti-parallel structure with bonds called hydrogen bonds. These hydrogen bonds link the pyrimidines and purines in the nitrogen bases together. In a process called complementary base pairing, guanine bonds to cytosine, and adenine bonds to thymine. This enhances the energy efficiency of the base pairings, and they will always be found in this pattern.

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The Function of Nucleic Acid

Each type of nucleic acid carries out a different function in the cells of all living things.


DNA is responsible for storing and coding genetic information in the body. The structure of DNA allows for genetic information to be inherited by children from their parents.

As the nucleotides adenine, thymine, guanine, and cytosine in DNA will only pair in a certain sequence (adenine with thymine, and guanine with cytosine), every time a cell duplicates the strand of DNA can specify the sequence in which the nucleotides should be copied. As such, accurate copies of DNA can be made and passed down from generation to generation.

Inside DNA, instructions for all the proteins an organism will make are stored.


RNA plays an important role in protein synthesis and regulates the expression of the information stored in DNA to make these proteins. It is also how genetic information is carried in certain viruses.

  • The various functions of RNA include:
  • Creating new cells in the body
  • Translating DNA into proteins
  • Acting as a messenger between DNA and ribosomes
  • Helps ribosomes choose the correct amino acids to create new proteins in the body.

These functions are carried out by RNA with different names. These names include:

  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)
  • Messenger RNA (mRNA).


However, not all nucleic acids are involved in processing the information stored in cells. The nucleic acid adenosine triphosphate (ATP), made up of an adenine nitrogenous base, a 5-carbon ribose sugar, and three phosphate groups, is involved in generating energy for cellular processes.

The bonds between the three phosphate groups are high energy bonds, and supply the cell with energy. All living cells use ATP for energy to allow them to carry out their functions.

To supply energy, the last phosphate group in the chain is removed, which releases energy. This process changes ATP to adenosine diphosphate (ADP). Removing two phosphate groups from ATP generates the energy needed to create adenosine monophosphate (AMP).

ATP can be created again through a recycling process in mitochondria that recharges the phosphate groups and adds them back onto the chain.

ATP is involved in the transportation of proteins and lipids in and out of cells, known as endocytosis and exocytosis respectively. ATP is also important in maintaining the overall structure of a cell as it helps to build the cytoskeletal properties of the cell.

In terms of specific bodily functions, ATP is important in muscle contraction. This includes the contractions made by the heart as it beats, as well as movements made by larger muscle groups.


Nucleic acid is an essential part of all living things and is the building block for both DNA and RNA. It is found in all cells and also in some viruses. Nucleic acids have a very diverse set of functions, such as cell creation, the storage and processing of genetic information, protein building, and the generation of energy cells.

Although their functions may differ, the structures of DNA and RNA are very similar, with only a few fundamental differences in their molecular make-up differentiating them.


  • Alberts, B. et al. Molecular biology of the cell. (2002). https://www.ncbi.nlm.nih.gov/books/NBK26821/
  • Bergman, J. ATP: the perfect energy currency for the cell. (2002). https://www.trueorigin.org/atp.php
  • BYJU (n.d.). https://byjus.com/biology/structure-of-rna/
  • MEDSimplified. (2017). https://www.youtube.com/watch?v=0lZRAShqft0

Last Updated: Jul 17, 2020

Written by

Lois Zoppi

Lois is a freelance copywriter based in the UK. She graduated from the University of Sussex with a BA in Media Practice, having specialized in screenwriting. She maintains a focus on anxiety disorders and depression and aims to explore other areas of mental health including dissociative disorders such as maladaptive daydreaming.

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