Nucleic acids are the organic materials present in an organism including 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.
Let us understand the basics of DNA structure, and its discovery.
What is DNA?
DNA – Deoxyribonucleic acid is a molecule which carries the genetic instructions or the hereditary materials which are used in the growth and development of all living organisms including the virus.
DNA is found in all living organisms and is mainly responsible for the inheritance of the human beings. The cells of the human body possess same DNA which is located in the nucleus of cells hence it is described as nuclear DNA and 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.
DNA was first recognized and identified by the Swiss biologist named Johannes Friedrich Miescher in the year 1869. The 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 the DNA is responsible for storing the genetic information of a human being.
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 as nucleotides and each nucleotide is comprised of three different components such as sugar, phosphate groups, and nitrogen bases.
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, thus forming a ladder-like structure.
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 hydrogen bonds present in between are responsible for holding the two strands together. 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.
DNA’s are coiled up forming chromosomes and each of 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. The 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 the 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.
- Cellular Metabolism.
- DNA Finger Printing.
- Gene Therapy.
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