What is Nucleotide?

A nucleotide is the basic building block of nucleic acids (RNA and DNA). A nucleotide consists of a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base.

The bases used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). In RNA, the base uracil (U) takes the place of thymine. DNA and RNA molecules are polymers made up of long chains of nucleotides.

what is Nucleotide

What is Nucleotide?

Nucleotides are organic molecules composed of a nitrogenous base, a pentose sugar,, and a phosphate.

They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules within all life forms on Earth. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver.

Nucleotides are composed of three subunit molecules: a nucleobase, a five-carbon sugar (ribose or deoxyribose), and a phosphate group consisting of one to three phosphates. The four nucleobases in DNA are guanine, adenine, cytosine, and thymine; in RNA, uracil is used in place of thymine.

Nucleotides also play a central role in metabolism at a fundamental, cellular level. They provide chemical energy in the form of 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, including amino acid, protein, and cell membrane synthesis, moving the cell and cell part, cell division, etc.

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+).

In experimental biochemistry, nucleotides can be radiolabeled using radionuclides to yield radionucleotides.

5-nucleotides are also used in flavor enhancers as a food additive to enhance the umami taste, often in the form of a yeast extract.

Characteristics of Nucleotides

A nucleotide is an organic compound made up of three subunits: a nitrogenous base, a five-carbon sugar, and a phosphate group. The sugar component may either be ribose or deoxyribose. Ribose is the sugar component of the nucleotides that make up RNA.

The deoxyribose sugar is the sugar component of DNA. Each phosphate group connects the sugar rings of two adjacent nucleotide monomers. The phosphate groups and the sugar moieties form the backbone of nucleic acid.

In DNA, the orientation of the two strands is in opposite directions. This is to allow complementary base pairing between nucleobase constituents. Apart from the long chain of nucleic acids, nucleotides also occur in cyclic forms.

Cyclic nucleotides form when the phosphate group is linked twice to the sugar moiety, particularly to the two hydroxyl groups of the constituent sugar.

Apart from the role of nucleotides as subunits of nucleic acids, they are also energy carriers. They carry chemical energy that the cell uses to fuel various cell activities. Adenosine triphosphate (ATP) is by far the most widely used.

Nucleosides vs. Nucleotides

Nucleotides should not be confused with nucleosides, which are also 5-carbon sugar with a nitrogenous base. Nucleosides do not have a phosphate group. When a nucleoside is bound to a phosphate group, it yields a nucleotide.

Thus, a nucleotide is also referred to as nucleoside monophosphate (if with only one phosphate group), nucleoside diphosphate (with two phosphate groups), or nucleoside triphosphate (when with three phosphate groups).

Depending on the pentose sugar component, a nucleoside may be a ribonucleoside or a deoxyribonucleoside. A ribonucleoside is a nucleoside with a ribose (sugar component).

Based on the nucleobase component, the ribonucleoside may be adenosine, guanosine, cytidine, uridine, or 5-methyluridine.

A deoxyribonucleoside is a nucleoside with deoxyribose. Similarly, based on the nucleobase component, a deoxyribonucleoside may be deoxyadenosine, deoxyguanosine, deoxycytidine, deoxythymidine, or deoxyuridine.

Also, depending on the nucleobase component, the nucleosides may be grouped into either the “double-ringed” purine or the “single-ringed” pyrimidine.

Classification of Nucleotides

The fundamental nucleotides are divided into purines and pyrimidines based on the structure of the nitrogenous base. The purine bases include adenine and guanine while the pyrimidine bases are thymine and cytosine, and uracil. In RNA uracil replaces thymine (thymine is produced by adding methyl to uracil).

The nucleobases that make up the nucleic acid are used to distinguish DNA from RNA molecules. In DNA, thymine complementary pairs with adenine whereas in RNA, uracil matches with adenine. The pairings of nucleobases C-G and A-T (or A-U in RNA) are referred to as base complements.

Types of Nucleotides

Examples of nucleotides with only one phosphate group:

  • Adenosine Monophosphate (AMP)
  • Guanosine Monophosphate (GMP)
  • Cytidine Monophosphate (CMP)
  • Uridine Monophosphate (UMP)
  • Cyclic Adenosine Monophosphate (Camp)
  • Cyclic Guanosine Monophosphate (Cgmp)
  • Cyclic Cytidine Monophosphate (Ccmp)
  • Cyclic Uridine Monophosphate (Cump)
  • Deoxyadenosine Monophosphate (Damp)
  • Deoxy Guanosine Monophosphate (Dgmp)
  • Deoxtcytidine Monophosphate (Dcmp)
  • (Deoxy)Thymidine Monophosphate (Dtmp)

Nucleotides with two phosphate groups:

  • Adenosine Diphosphate (ADP)
  • Guanosine Diphosphate (GDP)
  • Cytidine Diphosphate (CDP)
  • Uridine Diphosphate (UDP)
  • Deoxyadenosine Diphosphate (Dadp)
  • Deoxyguanosine Diphosphate (Dgdp)
  • Deoxycytidine Diphosphate (Dcdp)
  • (Deoxy)Thymidine Diphosphate (Dtdp)

Nucleotides with three phosphate groups:

  • Adenosine Triphosphate (ATP)
  • Guanosine Triphosphate (GTP)
  • Cytidine Triphosphate (CTP)
  • Uridine Triphosphate (UTP)
  • Deoxyadenosine Triphosphate (Datp)
  • Deoxyguanosine Triphosphate (Dgtp)
  • Deoxycytidine Triphosphate (Dctp)
  • (Deoxy)Thymidine Triphosphate (Dttp)