Difference Between Nucleotide and Nucleic Acid

Main Difference – Nucleotide vs Nucleic Acid

Nucleotide and nucleic acid are involved in the storage of genetic information in the nucleus of the cell. Nucleic acid is composed of a phosphate group and a nitrogenous base, which are attached to a pentose sugar. Nitrogenous bases found in nucleotides are adenine, guanine, cytosine, thymine and uracil. Polymerization of these nucleotides in different orders produces nucleic acids. The nucleic acid can be either RNA or DNA depending on the pentose sugar present in the monomer units. DNA and RNA are involved in the gene expression as well as the storage of genetic information in the cell. The main difference between nucleotide and nucleic acid is that nucleotide is the monomer of nucleic acid whereas nucleic acid is a chain of nucleotides, which is capable of storing genetic information in the cell.

This article looks at,

1. What is a Nucleic Acid
      – Definition, Structure and Composition, Function, Examples
2. What is a Nucleotide
      – Definition, Structure and Composition, Function, Examples
3. What is the difference between Nucleotide and Nucleic Acid

What is a Nucleic Acid

A nucleic acid can be either a DNA or RNA, which is a polymer of nucleotides. A phosphodiester bond is formed between 5′ phosphate group of the first nucleotide and the 3′ OH group of the second nucleotide by removing diphosphate in order to obtain the energy to form the bond. When ribose is the sugar in the nucleotide, the resultant polynucleotide is called RNA. On the contrary, when the pentose sugar is deoxyribose, the resultant polynucleotide is called DNA. The nitrogenous bases in RNA are adenine, guanine, cytosine and uracil. Nevertheless, in DNA, uracil is replaced by thymine.

DNA is a double-stranded molecule, where the two strands of the DNA are held together by hydrogen bonds forming between complementary nucleotides. Adenine is complementary to thymine and uracil whereas cytosine is complementary to guanine. DNA consists of a directionality in each of the two chains. One chain in the double-stranded structure bears a 3′ to 5′ directionality, while the other chain bears a 5′ to 3′ directionality. DNA is found inside the nucleus, storing the genetic information of the cell. RNA is a shorter molecule than DNA. RNA is formed during transcription of genes in the genome by RNA polymerase. Several types of RNA are found within the nucleus like mRNAs, tRNAs, rRNAs and microRNAs. Most of the RNA types are involved in the protein synthesis. The structure of DNA and RNA are shown in figure 2.

Figure 2: Structure of DNA and RNA

What is a Nucleotide

A nucleotide is a compound containing a nitrogenous base and a phosphate group attached with a pentose sugar, which can be either a ribose or a deoxyribose. Two types of nitrogenous bases can be attached to nucleotides: purine and pyrimidine. Purine bases are adenine and guanine, and pyrimidine bases are cytosine, uracil and thymine. Either one, two or three phosphate groups can be attached to the 5’ carbon of the pentose sugar. The dGMP and GMP nucleotides are shown in figure 1. 

Figure 1: dGMP and GMP Structure

Nucleotides are the monomers of nucleic acids. Polymerization of nucleotides, which contain ribose as the sugar, forms RNA and the polymerization of nucleotides, which contain deoxyribose as the sugar, forms DNA. Nucleotides also serve as an energy source. As an example, ATP is the widely using chemical energy source in many biochemical processes. The GTP also serves as the energy source for protein synthesis. On the other hand, cyclic AMP is involved in the signal transduction pathways of both nervous system and endocrine system. Other than that, dideoxynucleotides are used in sequencing for the chain termination. 

Difference Between Nucleotide and Nucleic Acid

Relationship

Nucleotide: Nucleotide is the monomer of nucleic acids.

Nucleic Acid: Nucleic acid is the polymer of nucleotides.

Composition

Nucleotide: Nucleotide is composed of a phosphate group and a nitrogenous base, which are attached to a pentose sugar.

Nucleic Acid: Nucleic acid is composed of a chain of nucleotides, which are linked by phosphodiester bonds.

Number of Phosphate Groups

Nucleotide: One to three phosphate groups can be contained in nucleotides.

Nucleic Acid: A single phosphate group is found in nucleic acids.

Function

Nucleotide: Nucleotides are polymerized to form DNA or RNA. They serve as an energy source and signal transducer. 

Nucleic Acid: Nucleic acids are involved in gene expression as well as the storage of genetic information.

Examples

Nucleotide: ATP, ADP, CMP, dGTP, ddATP are the examples of nucleotides.

Nucleic Acid: DNA and RNA are the examples of nucleic acids.

Conclusion

Nucleotides are the monomers of nucleic acids. Nucleotides consist of a nitrogenous base and a phosphate group attached to a pentose sugar. Two types of nucleic acids can be found depending on the type of the pentose sugar in the nucleic acid backbone. When the pentose sugar is ribose, the forming nucleic acid is RNA. On the other hand, when the pentose sugar is deoxyribose, the resultant nucleic acid is DNA. DNA is the most widely used nucleic acid in storing of genetic information in the cell. According to the nucleotide sequence on the DNA molecule, the genetic information can be stored in written form. RNA is involved in the process of gene expression. Therefore, the main difference between nucleotide and nucleic acid is in their relationship between monomers and polymers of each other.

Reference:
1. Lodish, Harvey. “Structure of Nucleic Acids.” Molecular Cell Biology. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 26 Mar. 2017.

Image Courtesy:
1.”Nucleotides”By Calibuon at English Wikibooks – Transferred from en.wikibooks to Commons by Adrignola using CommonsHelper. (Public Domain) via Commons Wikimedia
2.“RNA-comparedto-DNA thymineAndUracilCorrected” By Users Antilived, Fabiolib, Turnstep, Westcairo on en.wikipedia –  (CC BY-SA 3.0) via Commons Wikimedia