"Biology is the most powerful technology ever created. DNA is software, proteins are hardware, cells are factories.”- Arvind Gupta.
What Is DNA (Deoxyribonucleic Acid)?
DNA is a complex molecule that contains all of the information required to build and maintain an organism. DNA is found in the cells of all living things. In fact, nearly every cell in a multicellular organism contains the entire set of DNA needed for that organism.
However, DNA does more than just specify the structure and function of living things; it is also the primary unit of heredity in all organisms. To put it another way, when organisms reproduce, a portion of their DNA is passed down to their offspring.
But, exactly, what is DNA? This article provides answers to all of these questions, as well as a basic overview of the DNA discovery process.
All About The Discovery Of DNA
During the 1950s, Francis Crick and John Watson were part of a research project conducted at the University of Cambridge, England. The research focused on determining the structure of DNA. Besides Watson and Crick, Linus Pauling and Maurice Wilkins were also working in the same field.
In Maurice Wilkin's Lab, Rosalind Franklin was working on understanding the structure of DNA using X-ray crystallography. Watson and Crick utilized the data of Franklin and determined the structure of DNA. They also described the structure of DNA using Chargaff's rule which can be written as follows:
No. of purines= No. of pyrimidines.
DNA: the ultimate genetic material
DNA (Deoxyribonucleic acid) is a macromolecular, double-stranded helical structure, composed of a chain of polynucleotides. The polynucleotide chain in turn consists of nucleotides on one strand joined with each other through phosphodiester linkage, and with the nucleotides on the complementary strand via hydrogen bonding.
nucleotides = nucleosides + phosphate.
nucleosides= nitrogenous base + sugar
Location of DNA
DNA is located in the chromosomes present inside the nucleus of a cell. Apart from the nucleus, chloroplast and mitochondria also have their DNA, conserved in the course of evolution.
Structure of DNA
The four types of nitrogenous bases present in the DNA are Adenine (A), Cytosine ©, Guanine (G), and Thymine (T).
Out of these four, adenine and guanine are referred to as purines, whereas cytosine and thymine are pyrimidines. Purine is a double membraned ring nitrogenous compound whereas pyrimidines are single ringed nitrogenous compounds.
Adenine on one strand binds with the thymine on the complementary strand via 2 hydrogen bonds, whereas guanine on one strand pairs with cytosine on the complementary strand via 3 hydrogen bonds.
The two strands of DNA are antiparallel to each other. One end is referred to as 5' prime end because of the presence of a phosphate group attached to it, while the other end of the same strand is referred to as 3' prime end due to the presence of a free hydroxyl group at 3rd carbon atom of the deoxyribose sugar.
The backbone of DNA contains a deoxyribose sugar which is attached to a nitrogenous base via glycosidic linkage at the 2nd carbon position. There is a glycosidic linkage between the phosphate group and carbon at the 5th and 3rd carbon positions. The phosphodiester linkage joins two monomeric units (nucleotides) within a DNA strand.
The two strands of DNA are wounded in a right-handed double helix. There is a turn in the DNA strand after every 10 nucleotides. The helix pitch is 3.4 nm. The two nitrogen bases present on the complementary strands and bonded through hydrogen bonding are separated by the distance of 0.34 nm.
All Types of DNA
- A DNA - A DNA is wounded in a right-handed double helix. DNA on dehydration gets converted into A form. Such conversion protects DNA from harsh conditions like desiccation. In the right-handed helix of this DNA, there are 11 base pairs per turn. The distance between two consecutive base pairs is 2.56AO. The diameter of the helix is about 1.9nm.
- B DNA: B DNA is the most common form of DNA. It is wounded in a double helix. Under normal physiological conditions, the majority of DNA exists in b type conformation. The B DNA is about 1.9 m in diameter. In B DNA, the minor groove is narrower as compared to the major groove. The distance between the two consecutive base pairs is 0.34nm. It takes 10 base pairs to complete 1 turn.
- Z DNA: In Z DNA, a double helix is wounded in a zig-zag form. Moreover, the left-handed helix contains 12 base pairs per turn. The distance between two consecutive base pairs is 3.7AO. The diameter of the double helix is 19Ao.
Functions of DNA
The sole function of DNA is to contain information in the form of nucleotide sequences. This information is used to synthesize other molecular structures like proteins and RNA. With the advancement in technologies, DNA has been used to investigate criminal cases by using DNA fingerprinting. DNA tests are helpful in cases where the paternity of a child is to be determined.
Apart from DNA, RNA is also a type of genetic material in certain viruses. This ribonucleic acid stores information in the sequence of its ribonucleotides. In the course of evolution, several sophisticated enzymes have evolved that harnessed the information provided in the nucleotide sequence of DNA to form products like RNA and proteins.