DNA Structure

Nucleic acids are the organic materials present in all organisms in the form of DNA and RNA. These nucleic acids are formed by the combination of nitrogenous bases, sugar molecules and the phosphate groups that are linked by different bonds in a series of sequences. The DNA structure defines the basic genetic makeup of our body. Some virus may have RNA as their genetic material, but RNA has different functions in most of the organisms.

What is DNA?

DNA (abbreviated as Deoxyribonucleic acid) is a molecule that is responsible for carrying the hereditary materials or the genetic instructions that are required for the development and growth of all life on earth. This is also true for viruses as most of these entities have either RNA or DNA as their genetic material.

DNA – deoxyribonucleic acid, is an organic compound of complex molecular structure found in all prokaryotic and eukaryotic cells and in many viruses. DNA is found in all living organisms and is mainly responsible for the inheritance of human beings. The cells of the human body possess the same DNA which is located in the nucleus of cells. Hence, it is described as nuclear DNA. The DNA present in the mitochondria of the cell is termed as mitochondrial DNA which is inherited from the mother to the child. In humans, there are approximately 16,000 base pairs of mitochondrial DNA.

Who Discovered DNA?

The DNA was first recognized and identified by the Swiss biologist, Johannes Friedrich Miescher in 1869 during his research on white blood cells. The DNA double helix structure of a DNA molecule was later discovered through the experimental data by James Watson and Francis Crick. Finally, it was proved that it is responsible for storing the genetic information of a human being.

Structure of DNA

Structure of DNA

DNA is a long, double helix structure that resembles a ladder which is twisted at both the ends as shown in the above figure.

The DNA molecule is composed of basic materials called nucleotides and each nucleotide is composed of three different components such as sugar, phosphate groups, and nitrogen bases. The basic building blocks of DNA are nucleotides, which composed of a carbon -sugar group, a phosphate group, and a nitrogen base. The sugars and phosphates groups link the nucleotides together to form each strand of DNA. Adenine (A), Thymine (T), Guanine (G)  and Cytosine (C) are four types of nitrogen bases.

These 4 Nitrogenous bases pair together in the following way:  A – T and C – G . These base pairs are essential for the DNA’s double helix structure, which resembles a twisted ladder. The order of the nitrogenous bases determines the genetic code or the DNA’s instructions.

Structure of DNA

Among the 3 components of DNA, the sugar is the one which forms the backbone of the DNA molecule. It is also called as deoxyribose. The nitrogenous bases of the opposite strands form hydrogen bonds, forming a ladder-like structure.

Structure of DNA

The DNA molecule consists of 4 nitrogen bases namely adenine (A), thymine (T), cytosine (C) and Guanine (G) which completely forms the structure of a nucleotide. The A and G from a pair of purines and the C and T from pyrimidines. Both purines and pyrimidines differ as they have the carbon rings either single or double.

The two strands of DNA run in opposite directions. The two strands are held together by the hydrogen bond that is present between the two. The strands are helically twisted, where each strand forms a right-handed coil and 10 nucleotides make up a single turn.

The pitch of each helix is 3.4 nm. Hence, the distance between two consecutive base pairs (i.e., hydrogen-bonded bases of the opposite strands) is 0.34 nm.

Structure of DNA


DNA’s are coiled up forming chromosomes and each chromosome has a single molecule of DNA in it. Overall, human beings have around twenty-three pairs of chromosomes in them. These chromosomes are found in the cells of the nucleus. DNA’s play an important role in the process of cell division.

Functions of DNA

DNA is the genetic material which car­ries all the hereditary information which are coded in the arrangement of its nitrogen bases. Genes are the small segments of DNA, consisting mostly of 250 – 2 million base pairs, depending on the gene. A gene code for a polypeptide molecule, where 3 nitrogenous bases stand for one amino acid.

Thus, the sequence of a gene can be used to make a polypeptide, which then forms a protein. As every organism contains many genes in their DNA, different types of proteins can be formed. Proteins are the main functional and structural molecules in most of the organisms. Apart from storing hereditary information, DNA is also involved in:

  • Replication process: Transferring the genetic information from one cell to its daughters and from one generation to the next
  • Equal distribution of DNA during the cell division
  • Mutations: The changes which occur during the DNA sequences
  • Transcription
  • Cellular Metabolism
  • DNA Fingerprinting
  • Gene Therapy.

Stay tuned with BYJU’S to learn more in detail about the DNA, its structure, functions and its properties.

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DNA model was proposed by