Basic Components of Nucleic Acids – Purines and Pyrimidines

What are the components of nucleic acids? Before going to discuss this, you should know the basics of Nucleic acids and their components. Nucleic acids are organic polymers, composed of monomer units known as nucleotides. Nucleotides are energy-rich compounds that drive metabolic processes in all cells.

They also serve as chemical signals, key links in cellular systems that respond to hormones and other extracellular stimuli, and are structural components of a number of enzyme cofactors and metabolic intermediates.

There are very few different types of nucleotides. The main functions of nucleotides are information storage (DNA), protein synthesis (RNA), and energy transfers (ATP and NAD).

One of the important specialized pathways of amino acids and the synthesis of purine and pyrimidine nucleotides. These nucleotides are important for a number of reasons.

Nucleotides (Backbone unit of Nucleic Acids), shown in Figure 1, consist of a sugar, a nitrogenous base, and a phosphate. The sugars are either ribose or deoxyribose. They differ by the lack of one oxygen in deoxyribose. Both are pentoses usually in a ring form.

Most of them, not just ATP, are the sources of energy that drive most of our reactions.

  • ATP is the most commonly used source but GTP is used in protein synthesis as well as a few other reactions.
  • UTP is the source of energy for activating glucose and galactose.
  • CTP is an energy source in lipid metabolism.
  • AMP is part of the structure of some of the coenzymes like NAD and Coenzyme A. And, of course, the nucleotides are part of nucleic acids.

Neither the bases nor the nucleotides are required dietary components. These are the structural components of nucleic acids.

Basic Components of Nucleic Acids


What are the components of nucleic acids? Nucleic acids consist of Nucleotides. Nucleotides have three characteristic components. Here are 3 components of nucleic acids

Nitrogenous Bases Purines

Adenine (A) – Present in DNA & RNA

Guanine (G) – Present in DNA & RNA

Pyrimidines

Cytosine – Present in DNA & RNA

Thymine – Present in DNA only

Uracil – Present in RNA only

Sugar Moiety Deoxy Ribose Ribose
Phosphoric Acid Phosphoric Acid Phosphoric Acid

The components of nucleic acids are

  1. Nitrogenous Bases
  2. Sugar Moiety
  3. Phosphorus acid

a) Nitrogenous Bases

The nitrogenous bases are the derivatives of two-parent compounds. They are PURINES & PYRIMIDINES

Purines:

What are the purine bases found in nucleic acids? Purine bases found in nucleic acids and are heterocyclic compounds consisting of a pyrimidines ring and an imidazole ring fused together. The two purine bases are-

      • Adenine (6-Amino Purine): (C5H5N5), found in both RNA and DNA, is a white crystalline purine base, with Molecular weight 135.15 daltons and melting point 360 to  365 C.
      • Guanine (2-Amino-6-oxyPurine): (C5H5ON5), also found in both DNA and RNA, is a colorless, insoluble crystalline substance, with MW=151.15 daltons. It was first isolated from guano (bird manure), hence so named.
Purines and Pyrimidines
Basic Components of Nucleic Acids – Purines and Pyrimidines

Pyrimidines:

Pyrimidine bases consist of a six-membered ring with two nitrogen atoms. The pyrimidine bases are –

    • Cytosine (2-Oxy-4-amino pyrimidine): (C5H6O2N5), found in both RNA and DNA, is a white crystalline substance, with MW=111.12 daltons and a melting point 320 to 325 C.
    • Thymine (2, 4-dioxy-5-methyl pyrimidine): (C5H6O2N2), found in DNA molecules only, has MW=126.13 Daltons. It was first isolated from thymus, hence so named. Thymine is present in RNA only.
    • Uracil (2, 4-dioxy pyrimidine) (C4H4O2N2), found in RNA molecules only, is a white, crystalline pyrimidine base with MW=112.10daltons and a melting point 338 C.  Uracil is present in DNA only.
Structures of Pyrimidines
Basic Components of Nucleic Acids – Pyrimidines

b. Sugar moiety

Pentose sugar is present in DNA & RNA. It is present in their “β-furanose” from (close five number ring) and of β-configuration. Two types of pentose sugars present in the nucleic acid.

  • Ribose (present in RNA)
  • 2-Deoxyribose (present in DNA)
Sugar moiety in Nucleic acids
Sugar moiety in Nucleic acids – DeoxyRibose and Ribose

c. Phosphate

This is one of the fundamental components of nucleic acids.   It contains the monovalent hydroxyl groups and one divalent oxygen atom all are linked to the pentavalent phosphorus atom.

resonance of phosphate molecule

The base is joined covalently (at N1 of pyrimidines and N9 of purines) and the phosphate is esterified to the 5’-carbon. The N-glycosyl bond is formed by removal of the elements of water (Hydroxyl groups from pentose and Hydrogen atom from the base).

What are Mutations:

A mutation is any change in the DNA base sequence. Most mutations are harmful, few are neutral, and a very few are beneficial and contribute the organism’s reproductive success. Mutations are the wellspring of variation, variation is central to Darwin and Wallace’s theory of evolution by natural selection.  Check the details on Mutations and its types

Ribonucleic acid (RNA):

RNA was discovered after DNA. DNA, with exceptions in chloroplasts and mitochondria, is restricted to the nucleus (in eukaryotes, the nucleoid region in prokaryotes). RNA occurs in the nucleus as well as in the cytoplasm (also remember that it occurs as part of the ribosomes that line the rough endoplasmic reticulum). There are three types of RNA:

  • Messenger RNA (mRNA) is the blueprint for the construction of a protein.
  • Ribosomal RNA (rRNA) is the construction site where the protein is made.
  • Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time.

Adenosine triphosphate, better known as ATP (Figure 25), the energy currency or coin of the cell, transfers energy from chemical bonds to endergonic (energy absorbing) reactions within the cell. Structurally, ATP consists of the adenine nucleotide (ribose sugar, adenine base, and phosphate group, PO4-2) plus two other phosphate groups.

Energy is stored in the covalent bonds between phosphates, with the greatest amount of energy (approximately 7 kcal/mole) in the bond between the second and third phosphate groups. This covalent bond is known as a pyrophosphate bond.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.