Main Difference – DNA vs RNA Nucleotides
DNA and RNA nucleotides are the monomers of DNA and RNA, respectively. DNA nucleotides are adenine, guanine, cytosine and thymine. RNA contains uracil instead of thymine. DNA is widely used as the genetic material by organisms. RNA is used in the gene expression. The main difference between DNA and RNA nucleotides is that DNA nucleotides contain deoxyribose as their pentose sugar whereas RNA nucleotides contain ribose sugar as their pentose sugar in the molecule.
This article looks at,
1. What are DNA Nucleotides
– Definition, Characteristics, Function
2. What are RNA Nucleotides
– Definition, Characteristics, Function
3. What is the difference between DNA and RNA Nucleotides
What is a DNA Nucleotide
A DNA nucleotide is the monomer nucleotide, which can be found in DNA. It contains deoxyribose as the pentose sugar, which is attached to a nitrogenous base at its 1′ carbon and a phosphate group at its 5′ carbon. Deoxyribose is a monosaccharide, which is derived from ribose sugar by losing an oxygen atom on 2′ carbon. Hence, deoxyribose is more precisely called 2-deoxyribose. A labeled deoxyribose, which is derived from ribose sugar is shown in figure 1.
Figure 1: (Deoxy)Ribose
Nitrogenous bases in DNA are adenine, guanine, cytosine and thymine. Adenine and guanine are purine bases whereas cytosine and thymine are pyrimidine bases. In DNA, nucleotides are linked to form a chain and the order of the arrangement of nucleotides stores the genetic information of the cell. The sugar-phosphate backbone is formed by linking each nucleotide to the chain via phosphodiester bonds. Purine bases are base paired with pyrimidine bases in a complementary manner in order to hold the two DNA strands together in the double-helix. Adenine pairs with thymine and guanine pairs with cytosine.
DNA consists of 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. Lack of a hydroxyl group at its 2′ carbon in deoxyribose promotes the mechanical flexibility of DNA by forming the double-helix structure. DNA double-helix is also allowed to coil tightly in order to pack inside the nucleus in eukaryotes.
Figure 2: DNA Structure
What is a RNA Nucleotide
A RNA nucleotide is the monomer nucleotide found in RNA molecules. It contains ribose as the pentose monosaccharide, which is attached to a nitrogenous base at its 1′ carbon and a phosphate group at its 5′ carbon. Ribose contains two enantiomers: D-ribose and L-ribose. D-ribose is found in RNA. The main difference between ribose and deoxyribose is the 2′ hydroxyl group, which is borne by ribose. This 2′ hydroxyl group performs many roles in RNA. Nitrogenous bases in RNA are adenine, guanine, cytosine and uracil. The pyrimidine base, uracil replaces thymine in RNA. Hence, adenine pairs with uracil, rather than with thymine. RNA nucleotides are linked together to form the chain of nucleotides as in DNA. Since RNA is a linear molecule, the nucleotide chain only exists in its 5′ to 3′ direction. Chemical structure of RNA is shown in figure 3.
Figure 3: RNA Strand
RNA is incapable of forming the double-helix structure as in DNA due to the presence of 2′ hydroxyl group. Therefore, RNA is found as a linear molecule, which is only capable of forming double-stranded structures like hairpin loops. However, 2′ hydroxyl group is important in RNA splicing.
RNA is produced by transcription of DNA in the genome by the enzyme, RNA polymerase. Major types of RNA found in the cell are messenger RNA (mRNA), transfer RNA (tRNA) and ribozomal RNA (rRNA). mRNAs are the transcripts of genes. They are translated at ribosomes, which are formed by rRNAs. The relevant amino acids for the synthesis of the polypeptide are brought by tRNAs. Therefore, the main function of RNA is their role in protein synthesis. Some RNAs are also involved in the regulation of gene expression. Other than that, RNA nucleotides like ATP and NADH serve as the main source of chemical energy for biochemical reactions in the cell. cGMP and cAMP also serve as second messengers in signal transduction pathways.
Difference Between DNA and RNA Nucleotides
Pentose Sugar
DNA Nucleotides: Deoxyribose is found as the pentose sugar in DNA nucleotides.
RNA Nucleotides: Ribose is found as the pentose sugar in RNA nucleotides.
2′ Hydroxyl Group
DNA Nucleotides: DNA nucleotides lack a 2′ hydroxyl group in their deoxyriboses.
RNA Nucleotides: RNA nucleotides contains a 2′ hydroxyl group in their riboses.
Role of the 2′ Hydroxyl Group
DNA Nucleotides: The lack of a 2′ hydroxyl group allows the DNA to form a double-helix structure.
RNA Nucleotides: The presence of a 2′ hydroxyl group in ribose keeps the RNA as a linear molecule. This 2′ hydroxyl group also plays a role in RNA splicing.
Nitrogenous Bases
DNA Nucleotides: Nitrogenous bases found in DNA nucleotides are adenine, guanine, cytosine and thymine.
RNA Nucleotides: Nitrogenous bases found in RNA nucleotides are adenine, guanine, cytosine and uracil.
Function
DNA Nucleotides: DNA nucleotides are mainly involved in storage of genetic information.
RNA Nucleotides: RNA nucleotides are mainly involved in protein synthesis. They also have a role as energy sources and second messengers in signal transduction pathways.
Examples
DNA Nucleotides: DNA nucleotides are dATP, dAMP. dCTP, dGMP, etc.
RNA Nucleotides: RNA nucleotides are ATP, ADP, GTP, UTP, UMP, etc.
Conclusion
DNA and RNA nucleotides serve as the monomers of DNA and RNA, respectively. The pentose monosaccharides found in DNA nucleotides are deoxyribose, which allows the double-helix structure of DNA. Ribose is found as the pentose monosaccharide in RNA nucleotides. Due to the presence of 2′ hydroxyl group in ribose, RNA is unable to form the double-helix structure and exists as a linear molecule. Adenine, guanine and cytosine are the commonly sharing nitrogenous bases in both DNA and RNA nucleotides. Thymine in DNA nucleotides is replaced by uracil in RNA nucleotides. Both DNA and RNA are capable of forming the double-stranded structures by complementary base pairing. DNA is mainly involved in the storage of genetic information in the cell. RNA has its function in protein synthesis. However, the main difference between DNA and RNA nucleotides is their pentose sugar and the nitrogenous bases they share.
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.
2.”Ribose and Deoxribose.” Pearson – The Biology Place. N.p., n.d. Web. 26 Mar. 2017.
3.”Structural Biochemistry/Nucleic Acid/Difference between DNA and RNA.” Structural Biochemistry/Nucleic Acid/Difference between DNA and RNA – Wikibooks, open books for an open world. N.p., n.d. Web. 26 Mar. 2017.
Image Courtesy:
1.”DeoxyriboseLabeled” Di Adenosine (English Wikipedia User) – English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2.”DNA chemical structure 2″ By Thomas Shafee – Own work (CC BY 4.0) via Commons Wikimedia
3.”RNA chemical structure adenine”By Narayanese (talk) – Own work (Original text: Self-made.) (Public Domain) via Commons Wikimedia
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