NUCLEIC ACIDS: THE BUILDING BLOCKS OF LIFE

Nucleic acids are chain-like molecules that serve as main information-carrying entities. They issue instructions for the synthesis of protein which leads to every vital functioning of life from breathing to digesting. They are the encoder of code that allows the transmission of genetic information. 

There are two main categories of classification for nucleic acids: deoxyribonucleic acid and ribonucleic acid. These building blocks of life were discovered in 1869 by Friedrich Miescher, a renowned Swiss biochemist. 

In this article, we will explore the structure, properties and chemical composition of nucleic acids and how they make up life as we know it. 

Structure and Composition:

Polynucleotides or long chainlike molecules, which are made up of several almost similar building units called nucleotides, form up the nucleic acids. 

A nitrogenous base that is aromatic in nature is connected to a pentose  (which is a five-carbon chain) sugar, and that in turn is further attached to a phosphate group present in each nucleotide. 

Adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U) are the four bases that contain in themselves nitrogen and are found in each nucleic acid (which can be understood as basic constituent bases of nucleic acid). Bases A and G constitute purines, while bases C, T, and U are collectively termed pyrimidines. The nucleotides A, C, and G are found irrespective of composition in all nucleic acids occurring; T, on the other hand, is only found in the composition of  DNA, while U can be discovered only in the formation of RNA. 

The absence of a hydroxyl group (OH) from the 2′ (carbon attached to two other carbons) carbon of the ring differentiates the pentose sugar in DNA (2′-deoxyribose) from sugar present in RNA (ribose).

A nucleoside is a specialised sugar that is connected to one of the bases in a unique way such that it does not have a phosphate group linked by the side of it. 

If we bridge the 5′-hydroxyl group to one sugar, which is the 3′-hydroxyl group on another sugar in the chain, the phosphate group combines with successive sugars’ leftover ends. Phosphodiester bonds are identical in RNA and DNA  as these nucleoside connections or linkages. 

 Synthesis 

Nucleotides are made in the cell from easily available precursors. The pentose, which is a five-carbon ring phosphate pathway or network, is used to encapsulate the ribose phosphate as a part of both purine (A, G) and pyrimidine (C, T, U) nucleotides. The hex atomic pyrimidine ring is linked to the ribose phosphate only after its formation. Assembly of adenine or guanine, coupled to ribose phosphate, form rings of purine. 

The end product in both circumstances is a nucleotide with a phosphate bonded to the sugar’s 5′ carbon. Eventually, the kinase enzyme helps in the addition of phosphate group to ribonucleoside triphosphate, which is the precursor of RNA, followed by utilisation of ATP as phosphate donor.2′-hydroxyl group is eliminated from ribonucleoside diphosphate for the formation of deoxyribonucleoside diphosphate.

Another kinase then adds another phosphate group from ATP to make deoxyribonucleoside triphosphate, the immediate precursor of DNA. RNA is regularly generated and destroyed during normal cell metabolism. Purine is recovered as the matching nucleotide, whereas pyrimidine is recovered as the nucleoside.

 Properties

Hydrogen bonding interactions between complementary base pairs hold the strands of the DNA double helix together. The hydrogen bonds in DNA in solution are easily broken, causing the two strands to separate—a process known as denaturation or melting. 

The absorption of ultraviolet (UV) light (a form of energy with photons)  with a wavelength of 260 nanometres can be employed to measure the melting of DNA and, specifically, reassociation. Absorption is relatively mild when DNA is double-stranded. Still, when DNA happens to be a single-stranded one, the unstacking of the bases can yield an increased absorption which is termed or known as hyperchromicity.

Nucleases are enzymes that cleave the phosphodiester backbone of DNA hydrolytically. Endonucleases cleave in the midst of chains, whereas exonucleases degrade the chain selectively from the end. Some nucleases act on both single-stranded and double-stranded DNA.

Mutations in the genetic material can occur due to chemical alteration of DNA. Purine residues are lost when cells are exposed to acid, yet particular enzymes exist in cells to repair these injuries.

Circular DNA molecules present in plasmids and bacterial chromosomes can take on a variety of topologies. The first is active supercoiling, which entails cleaving one DNA strand, winding it one or more times around the complementary strand, and then resealing the molecule. 

The winding and relaxing of supercoiled DNA are catalysed by enzymes known as gyrases and topoisomerases. The DNA in eukaryotes’ linear chromosomes usually is tightly bound by proteins at various locations, allowing the intervening lengths to be supercoiled.

Conclusion:

Nucleic acids are the basic building blocks that influence our life characteristics and behaviours. It imparts us with our unique information and a distinctive identity. Studying nucleic acids is of great importance to humanity. The ability to mobilise and transform these bases to our advantage has great potential for humanity, especially in the field of genetic diseases and abnormalities.