What is DNA?

Nucleic Acid is one of the organic materials which is present in all organisms in the form of RNA or DNA.

DNA is generally a double helical structure formed by nitrogen bases, sugar molecules and the phosphate groups which are linked by various bonds in a series of sequences.

This molecule is very important in determining the genetic trait of an organism.

DNA is generally defined as the group of molecules which are responsible for carrying and transmitting hereditary materials and genetic instructions from present to future generations.

It also consists of unique molecular structure and it is present in all prokaryotic and eukaryotic organisms. This type of genetic materials is also found in viruses, but it is found in the form of RNA where all other organisms contain DNA.

On exceptional Human Immunodeficiency Virus has RNA but when it enters into a host cell it transforms into a DNA.

DNA also plays an important role in synthesizing the proteins apart from inheriting the characters. Where the nucleus of the cell is made up of Nuclear DNA in all living organisms. Which helps in coding the vast variety of genomes when mitochondria and plastid DNAs are busy with performing other functions.

The DNA that is present in mitochondria is termed as Mitochondrial DNA which is inherited from mother to the offspring.

In human beings, there are about 16,000 base pairs of mitochondrial DNAs however the other cell organelles like plastids and also have their own DNA which an important role in plants during the process of photosynthesis.

Types of DNA

I. A-DNA

It is generally a double helix right-handed DNA. Which is found similar to that of B-form. It is generally in a dehydrated form which helps in protecting the DNA from desiccation and other extreme conditions. Whereas protein binding removes the solvent from this DNA and the DNA obtains its A-form.

II. B-DNA

It is one of the right-handed helixes which a majority of DNA contains as it is the most common type of configuration. Mostly this type of DNA is found in majority of cases during normal physiologic conditions.

III. Z-DNA

This type of DNA is one of the left-handed double helixes where the double strand winds up in a left in a zig-zag pattern. This was first observed by Alexander Rich, after his discovery only the other scientists came to a conclusion that DNA play an important role in genetics.

Discovery of DNA

DNA was first Observed and discovered by Swiss biologist, Johannes Friedrich Miescher in the year 1869 while undergoing his research in white blood cells.

Later the double helical structure was discovered by James Watson and Franchis Crick through his experimental data and later on, it was concluded that DNA is responsible for storing all the genetic information.

Structure of DNA

The DNA structure was generally considered as a twisted ladder. Which is often described as double helix. It is a nucleic acid which are made up of nucleotides which are considered as the basic unit of DNA.

Each nucleotide is composed of three different types of components such as sugar, phosphate groups and nitrogen bases.

Hence the nucleotide is the basic unit of DNA, it is made up of sugar groups, phosphate group and a nitrogenous base. Where the sugar and phosphate groups are linked together by a nucleotide from the either strand of DNA.

It also consists of four nitrogen bases namely Adenine (A), Guanine(G), Thymine (T) and cytosis(C). Where in these nitrogenous bases, adenine combines only with Thymine (T) and Guanine pairs up only with Cytosine.

The order of these nitrogenous bases helps in determining the genetic information of the DNA.

Considering all these components of DNA, sugar is one of the most important components which forms a back bone of the molecule.

It is also called as Deoxyribose, where the opposite strands form a hydrogen bond and results in a formation of a ladder.

The four nucleotides of a DNA which is known as Adenine (A), Thymine(T), Guanine(G), Cytosine(C). which are important in forming the bases of the nucleotides. Where here adenine and thymine are referred to as purines, and guanine and cytosine are referred to as pyrimidines.

Each strands of DNA coil around each other to form a right-handed coil structure resembling a twisted ladder with the presence of base pair in between them.

The pitch of the helix is about 3,4nm and the distance between two strands is about two base pairs where the distance is about 0.34nm.

The DNA coils up to form chromosomes and each chromosome has a single molecule of DNA. In such a way the human beings have about twenty-three pairs of DNAs which is essential for the process of cell division.

Chargaff’s Rule

According to Chargaff’s rule the number of nitrogenous bases in the DNA must be equal, which means that the amount of Adenine should equals the amount of Thymine and amount of Guanine equals to the amount of Cytosine.

It is said that DNA in any cells of an organism should have purine and pyrimidine in the ratio of 1:1.

Function of DNA

DNA is a genetic material which helps in carrying hereditary material from present to the future generations. Where genes are considered as a small segment of DNA which consists of about 2 million base pairs.

Three nitrogenous base pairs make up one amino acid. A gene codes to form a polypeptide molecule.

Polypeptide molecules are further folded to make secondary, tertiary and quaternary structures to form different proteins. As all organism contains gene in their DNA, they form specific proteins depending upon the need of an organism.

DNA also performs in other activities like replication where the genetic information is passed from parent cell to the daughter cells during the process of cell division.

Mutation also occurs at some stages which leads to change in sequence of DNA.

Transcription, follows other cellular metabolism and it also helps in DNA finger printing and also in gene therapy treatments.

DNA: A Polymer?

DNA is refereed to as a polynucleotide molecule because it is made up of several nucleotides such as deoxy adenylate(A), deoxy guanylate(G), deoxycytidylate(C) and deoxy thymidylate(T) which are together involved in forming the polynucleotides.