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Nucleic Acid – Definition, Function, Structure, and Types

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  • Last Updated : 04 Jul, 2022
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According to what we have learned, nucleic acids are one of the most significant types of macromolecules that are found in humans. They are the keepers of all the information about our genes that we transmit on to subsequent generations. Let us learn more about the strange structure of nucleic acids, shall we? Repetitive monomers are the building blocks of nucleic acids, precisely as they are in all other types of biomolecules. These repeating units, also known as monomers, are referred to by their technical term, nucleotides. These are the components that go into making up nucleic acids. Nucleotides When we’re in the midst of discussing the structure of nucleic acids, let’s take a look at nucleotides. Nucleic acids are composed of smaller building blocks called nucleotides. A nucleotide may be broken down into component parts, referred to as the “three essential building blocks.” Those three aspects are as follows:


Typically, this is sugar with five carbons. i.e a pentose. these sugars, together with the phosphate groups found in nucleotides, combine to create a bond. The carbohydrate that is found in the biomolecule of DNA is deoxyribose, while the carbohydrate in the biomolecule of RNA is ribose.

The Group of Phosphates

In other words, they are the phosphates that are derived from the inorganic substance known as phosphoric acid. H3PO4. They establish an ester bond by combining forces with the sugars present in the nucleotides. Phosphate groups might show up in nucleic acids in a variety of different combinations.

Nitrogenous Base

In all, there are five bases that include nitrogen. On the other hand, in the molecule that makes up a nucleic acid, there are never more than four.Adenine, Cytosine, Guanine, The mineral thymine (only present in DNA), Uracil (only present in RNA) 


Purines and pyrimidines are the common nucleotides found in genetic material of human beings. Both classes have molecules that are nonpolar and flat, like pyridine. Each pyrimidine is made up of a 1 heterocyclic organic ring, just like pyridine. A pyrimidine ring and an imidazole ring are combined to form the purines. These two rings are brought together to form the purines.Base of nitrogen in nucleic acids
Pyrimidines and Purines it is crucial to know that there are two base classes of nitrogenous bases. Nitrogenous bases all have one thing in common: a ring with 6 faces that has four carbon atoms and two nitrogen atoms. A purine has one more carbon atom and two more nitrogen atoms, which together make an extra five-sided ring. A nitrogenous base of pyrimidine has only one ring with six sides. Each nitrogenous base has a different set of bonds, which means that it works in a different way in DNA or RNA.

Nitrogenous Base

While there are many nitrogen – containing bases, the 5 most essential ones are the ones that are present in DNA and RNA. These nitrogen-containing bases serve as potential transporters in biological processes in addition to being found in DNA and RNA. Adenine(A), guanine(G), cytosine(C), thymine(T), and uracil(U)  are their respective names. To make DNA and RNA, each base has what is called a “complementary base” that it only binds to. The genetic code is based on how the complementary bases work together.



The purines are adenine and guanine. The chemical symbol for adenine is most often represented by the letter A. In DNA, thymine is the base that goes with it. Adenine is made up of the atoms C5H5N5. In RNA, uracil bonds with adenine.
To make nucleotides, adenine and the other bases link up with phosphate groups and either the sugar ribose or the sugar 2′-deoxyribose. The names of the nucleotides are similar to the names of the bases, but they end in “-osine” for purines (like “adenosine triphosphate” for adenine) and “-idine” for pyrimidines (e.g., cytosine forms cytidine triphosphate). The number of phosphate groups on a nucleotide is shown by its name: monophosphate, diphosphate, or triphosphate. Both DNA and RNA are assembled from nucleotides, which may be thought of as the fundamental components. The double helix shape of DNA is made by hydrogen bonds between purine and its complementary pyrimidine. Hydrogen bonds can also speed up reactions.

Adenine has the following qualities:

Adenine is one of the two purine nucleobases that are used to make nucleotides in nucleic acids. The other one is guanine. Two hydrogen bonds hold adenine to thymine in DNA. This helps keep the nucleic acid structures stable. RNA is used to make proteins. Adenine binds to uracil in RNA. When linked to ribose, adenine makes the nucleoside adenosine. When linked to deoxyribose, adenine makes the nucleoside deoxyadenosine. ATP, also known as a nucleoside triphosphate, is produced from adenosine by the addition of 3 separate phosphate groups. Adenosine triphosphate is used in the metabolism of cells as a basic way to move energy from one chemical reaction to another.


Guanine is a purine, and the capital letter G stands for it. It may be represented chemically as C5H5N5O. In both DNA and RNA, guanine forms a covalent link with cytosine. Guanine makes guanosine, which is a type of nucleotide. Purines are found in large amounts in meat, especially in organs like the liver, brain, and kidneys. Plants like peas, beans, and lentils only have a small amount of purines.

Guanine has the following qualities:

Guanine, adenine, and cytosine are all found in both DNA and RNA. Thymine, on the other hand, is usually only found in DNA, and uracil is usually only found in RNA. Guanine has two tautomeric forms: the keto form, which is the most common one (see figures), and the rare enol form. Three hydrogen bonds hold it to cytosine. The amine group in cytosine is the one that contributes to the formation of the H- bond. On the other hand, the C-2 carbonyl functional group and the N-3 amine functional group are the ones that accept the H- bond. The carbonyl group at C-6 in guanine is the hydrogen bond acceptor. The hydrogen bond donors are a group at N-1 and an amino group at C-2.


5-methyl uracil is another name for thymine. Thymine is a pyrimidine that binds to adenine in DNA. Thymine is written with a capital letter T. The formula for this is C5H6N2O2. 

Features of thymine

It  is a pyrimidine nitrogen base. It is made from uracil with a methyl group in place of the hydrogen at the fifth position. In humans, E.coli, and rodents, it serves as a metabolite and plays a function in the metabolic process. It is a nucleobase made of pyrimidine and a pyrimidone.


The capital letter C stands for cytosine. It covalently bonds to the guanine found in DNA and RNA. In the Watson-Crick base pairing process, cytosine and guanine make three hydrogen bonds with each other. This is how DNA is made. Cytosine is made up of the atoms C4H4N2O2. Cytidine is the nucleotide that is made out of cytosine.

Characteristics of cytosine

Cytosine is a type of pyrimidine base that pairs with guanine. It may be present in the RNA as well as the DNA. Cytosine is an aminopyrimidine, which is pyrimidine-2-one with an amino group at position-4. It functions as a metabolites in human cells, as well as in E.coli cells, Saccharomyces cerevisiae cells, and mouse cells. 


Uracil is like thymine that has been stripped of its methyl group. Uracil is shown by the letter U with a capital letter. The formula for this is C4H4N2O2. In nucleic acids, it is linked to adenine in RNA. The nucleotide uridine is made up of uracil.
In nature, there are many other nitrogenous bases, and the molecules can also be found in other compounds. For example, pyrimidine rings can be found in nucleotides, thiamine (vitamin B1), and barbituates. Some meteorites also have pyrimidines, but no one knows where they came from. Nature also has xanthine, theobromine, and caffeine, which are all purines.

Uracil has the following qualities

By forming bonds with ribose and phosphates, it helps make many enzymes that are needed for a cell to work. Uracil is a coenzyme and an allosteric regulator that is used in both animal and plant reactions. uracil has these traits:

Composition of DNA and RNA

In DNA, the bases pair up like this: (A-T), (G-C). Because uracil is utilised in place of thymine in RNA, the base-pairing consists of the following: (A-U), (G-C) The nitrogenous bases are in the middle of the double helix of DNA, and the backbone of the molecule is made up of the sugars and phosphates in each nucleotide. When a DNA helix splits, such as when DNA is copied, complementary bases attach to each half so that two copies can be made that are the same. For translation, when RNA is used as a pattern to make DNA, complementary bases are used to build the DNA molecule from the base sequence.
Because purines and pyrimidines work well with each other, cells need about the same amount of each. In a cell, the production of both purines and pyrimidines is self-inhibiting. This keeps the balance of the cell. When one is made, it stops more of the same thing from being made and starts making its opposite.

The Function of DNA

DNA is the genetic substance that stores all of the information about an individual’s ancestry. The tiny sections of DNA known as genes typically have between 250 and two million base pairs in their sequence. A gene contains the instructions for making a polypeptide molecule; the sequence of three nitrogenous bases stands in for 1 amino acid.
In order to generate various proteins, polypeptide chains must first undergo further folding into secondary, tertiary, and ultimately quaternary structures. Because the DNA of every creature has a diverse collection of genes, a wide variety of proteins may be produced. In the majority of living things, proteins serve as the primary morphological and anatomical molecules.
DNA, in addition to storing information about a person’s genetic make-up, is involved in the following processes: 

  • The process of replication includes the transmission of genetic information from one generation to the subsequent generation.
  • Transcription
  • Cell metabolism
  • Deoyribosenucleicacid fingerprinting
  • Genetic manipulation 
  • Gene expression

The basic roles of RNA are as follows

• Assist in the process by which DNA is translated into proteins
• Participates in the production of proteins in the role of an adapter molecule
• Functions inside the cell as a messenger between the ribosomes and the DNA in the nucleus of the cell.
• They are responsible for transporting genetic information in all of the body’s cells.
• Motivates the ribosomes to choose the correct amino acid, which is essential for the creation of unique biomolecules in the human body.

Conceptual Question

Question 1: What are the three distinct forms of DNA? 


  • A-DNA 
  • B-DNA 
  • Z-DNA

Question 2: What makes Z-DNA unique in comparison to other types of DNA?


The Z-DNA molecule has a left-handed double helix structure. The helix has a jagged pattern that goes to the left as it spirals. In contrast, both A-DNA and B-DNA are examples of right-handed DNA.

Question 3: What kind of DNA is discovered in human beings?


B-DNA may be discovered in human beings. The construction has a right-handed dual helical orientation.

Question 4: What kinds of molecules are DNA and RNA made up of?


Except for the base pairs, the polymers of nucleotides that make up DNA and RNA are almost similar to one another. In RNA, the nucleotide thymine is switched out for the base uracil, but in DNA, the thymine base is preserved.

Question 5: Where is it possible to get both DNA and RNA?


Both the nucleus and the mitochondria of a cell contain DNA. Deoxyribosenucleicacid would be detected in the cytoplasm as well. In the meanwhile, RNA may be located in the cytoplasm, the nucleus, and in ribosomes as well.

Question 6: How does the process of propagation take place in RNA and DNA?


DNA has the ability to duplicate itself, but RNA does not; instead, it must be transcribed from DNA in order to be produced when it is needed. DNA can replicate itself.

Question 7: Why is DNA considered to be superior to RNA as genetic material?


The sugar known as deoxyribose that is found in DNA has one less hydroxyl group that carries oxygen. DNA is a nucleic acid that is more persistent than any of the other nucleic acids. On the other hand, DNA is less reactive than RNA, which is due to DNA’s presence of the sugar ribose. As a consequence of this, DNA is a superior genetic material over RNA.

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