DNA is an abbreviation for deoxyribonucleic acid. It is made up of monomers called nucleotides. There are thousands of nucleotides in DNA. They can be termed as hereditary molecules as they carry unique codes of information which reveals your biological background. By just examining the sequence of the nucleotides, you can find out the ancestral information of a person.
A nucleotide is a monomer which constitutes a nitrogenous base, a pentose sugar and a phosphate group. This monomer polymerizes and forms a polynucleotide. There combination differentiates them into RNA or DNA. Nucleotides in RNA and DNA play a very vital role in the life process.
What do Nucleotides in DNA Consist of?
Nucleotides behave as the genetic information carrier. You will be surprised to know that a bacterium known as E.coli has 4 million nucleotides in its DNA. Nucleotides present in DNA consists of three molecules - a nitrogenous base, a pentose sugar and a phosphate group.
Nucleotide has a nitrogenous base which is hetrocyclic in structure. Purines and pyrimidines are the two types of bases found in the nucleotides which are further classified into adenine (A) and guanine (G) as purines, and thymine (T) and cytosine (C) as pyrimidines. The pair or bond always forms between A to T and G to C or reverse. The bond between purines and pyrimidines is always a hydrogen bond.
In nucleotide, 5 carbon sugar molecules are present with 3 oxygen. This makes it a pentose sugar. In DNA, it is deoxyribose sugar nucleotide which further becomes deoxyribonucleic acid. Combination of nitrogenous base and pentose sugar is known as nucleosides. But nucleosides are different from nucleotides as they lack phosphate group.
A phosphate group in a nucleotide can be a monophosphate , diphosphate or a triphosphate.
Structure of a Nucleotide
In a nucleotide structure, sugar, base and phosphate form a polynucleotide which is known as deoxyribonucleic acid or DNA. It has a double helical structure and two strands of double helix are always complementary to each other. Both the strands travel in opposite direction hence, the structure can also be called an anti parallel structure. The sugar and phosphate group makes the back bone of the structure and the base in the center makes a bond with the complementary base pair of the opposite strand. The bond is not so strong but when it forms a whole long string, the bond becomes strong enough to hold the structure.
Sequencing of Nucleotides
The genetic or nucleotide sequencing in a DNA depends upon the combination of the phosphate group, nitrogenous base and pentose sugar. The codes are unique as they carry information about one's biological background. DNA has a double helical structure therefore, for every sequence there is a complementary sequence. For example, if the sequence is GTAA then the complementary sequence will be TTAC. Hence, for every strand in DNA sequencing there is a complementary strand.
Cell breakdown or cell division is a common phenomenon and when a cell is divided, it replicates or makes its exact copy. In the same way, the nucleotides present in DNA also divide, and DNA replication take place. The replication should be same as the information should not be changed. It should be passed from the parent cell to the newborn cell with the same set of information. The DNA divides and then the strand is replicated by an enzyme known as DNA polymerase. Polymerase finds a suitable base pair to make a complementary strand. This process is supported by many other mechanisms and a replicated double helical structure of a DNA is formed.
Nucleotides play a very important role in DNA testing, DNA fingerprinting, forensic science and other DNA researches. Hope this information will justify the nucleotide as hereditary molecule and its vital role in carrying the information from one generation to the other.