NUCLEOTIDES (STRUCTURE AND TYPES)
- Nucleic acid which is the essential biomolecule for the life form on earth polymeric macromolecule formed from nucleotide monomer. Nucleotides are phosphate ester of a nucleoside. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver.
- Nucleotides that are found in DNA are four nucleobases guanine, adenine, cytosine and thymine, in RNA, uracil is present on the place of thymine.
- Nucleotides also plays a vital role in metabolism at a fundamental, cellular level. They provide chemical energy—in the form of the nucleoside triphosphates, adenosine triphosphate (ATP), guanosine triphosphate (GTP), cytidine triphosphate (CTP) and uridine triphosphate (UTP)—throughout the cell for the many cellular functions that demand energy, In addition, nucleotides participate in cell signaling (cyclic guanosine monophosphate or cGMP and cyclic adenosine monophosphate or cAMP), and are incorporated into important cofactors of enzymatic reactions (e.g. coenzyme A, FAD, FMN, NAD, and NADP+
- The structure of every protein, and ultimately of every biomolecule and cellular component, is a product of information programmed into the nucleotide sequence of cellular (or viral) nucleic acids. The ability to store and transmit genetic information from one generation to the next is a fundamental condition for life.
STRUCTURE OF NUCLEOTIDE
Nucleotide is composed of three components :-
- Five-carbon sugar molecule
- A base that has nitrogen
- A ion of phosphoric acid
- Sugar in nucleic acid are of two types ribose and deoxyribose sugar. Ribose sugar is having five carbon monosaccharides with a hydroxyl group attach to each carbon.
- Whereas deoxyribose sugar is also five carbon monosaccharide but lacks one oxygen at atom two position. and the hydroxyl group at second position is replaced by hydrogen atom.
NITROGENOUS BASE :-
- Nitrogenous base is covalently linked to C1 of the sugar residue. The nitrogenous bases are planar, aromatic, heterocyclic molecules which, for the most part, are derivatives of either purine or pyrimidine.
- The major purine components of nucleic acids are adenine( 6-aminopurine) and guanine ( 6-0xy-2-aminopurine) residues. Purine are double ring structure. The purines form glycosidic bonds to ribose via their N9 atoms. Adenine has amino group on carbon six position. Guanine has an amino group at carbon two position and carbonyl group at carbon.
- The two major pyrimidine bases found DNA are thymine (5-methyl-2,4-dioxyprimidine) and cytosine (2-oxy-4-aminopyrimidine) and in RNA are uracil (2,4-dioxypyrimidine) and cytosine. Thymine contain methyl group at carbon five position with carbonyl group at carbon 4 and carbon 2 position. Uracil is similar thymine but lacks methyl group at carbon 5 position
TYPES OF NUCLEOTIDES
- The chemical formula of adenine is C5H5N5. Adenine (A).
- Adenine performs various function such as it binds with thymine in DNA and with uracil in RNA.
- Other than that it is present in ATP which is also known as energy currency of cell.
- It is also precursor of 6-amino purine.
- The chemical formula of the pyrimidine thymine is C5H6N2O2.
- Its symbol is T and it is found in DNA but not RNA.
- In DNA thymine attach with adenine with two hydrogen bonds.
- Thymine is also known as 5- methyluracil.
- It is present in both prokaryotic and eukaryotic cells but is absent in RNA viruses.
- The chemical formula of the purine guanine is C5H5N5O.
- Guanine (G) binds only to cytosine (C), by forming triple bond in both DNA and RNA.
- Guanine can be use as energy source as in GTP.
- It can help in vision by acting as second messenger.
- It act as second messenger in other pathway also including in smelling.
- The chemical formula of the pyrimidine cytosine is C4H5N3O.
- Its symbol is C.
- This base is found in both DNA and RNA.
- Cytidine triphosphate (CTP) is an enzyme cofactor that can convert ADP to ATP.
- Cytosine can spontaneously change into uracil.
- If the mutation is not repaired, this can leave a uracil residue in DNA.
- Uracil has the chemical formula C4H4N2O2.
- Uracil (U) is found in RNA, where it binds with adenine (A).
- Uracil is the demethylated form of the base thymine.
- The molecule recycles itself through a set of phosphoribosyltransferase reactions.
- It is a weak acid.
FUNCTION OF NUCLEOTIDES
Nucleotides are basically associated with the function of the formation of polynucleotide i.e, nucleic acid. Nucleic acid carries all sort of information. They store, transmit and translate genetic information. They perform several function to regulate our physiology other functions of nucleotides are as follows :-
- Formation of energy currency like ATP, GTP.
- Act as precursor for several important coenzymes NAD+ and NADP+
- Serving as precursor for secondary messenger like cyclic AMP and cyclic GMP.
- Allosteric regulator of many enzymes through ATP example glycogen phosphorylase activated by ATP and inactivated by ADP.
The amino acid sequence of every protein in a cell, and the nucleotide sequences of every RNA, is specified by a nucleotide sequence in the cell’s DNA. A segment of a DNA molecule that contains the information required for the synthesis of a functional biological product, whether protein or RNA, is referred to as a gene. A cell typically has many thousands of genes, and DNA molecules, not surprisingly, tend to be very large. The storage and transmission of biological information are the only known functions of DNA.
Nucleotides have a variety of roles in cellular metabolism. They are the energy currency in metabolic transactions, the essential chemical links in the response of cells to hormones and other extracellular stimuli, and the structural components of an array of enzyme cofactors and metabolic intermediates. And, last but certainly not least, they are the constituents of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), the molecular repositories of genetic information. The structure of every protein, and ultimately of every biomolecule and cellular component, is a product of information programmed into the nucleotide sequence of cellular (or viral) nucleic acids. The ability to store and transmit genetic information from one generation to the next is a fundamental condition for life.
- Lehninger principles of biochemistry seventh edition By David L. Nelson and Michael M. Cox
- Life sciences fundamental and practices sixth edition, pathfinder publication By Pranav Kumar and Usha Mina