Which of the following is nucleic acid ?

Question

Accepted Answer

The correct option is 1:

The correct answer is Option 1, RNA and DNA, because these two macromolecules are the definitive and primary classes of nucleic acids found in all living organisms. Nucleic acids are vast biopolymers made up of repeating monomer units called nucleotides. These molecules are fundamentally responsible for storing, transmitting, and expressing genetic information within a cell. DNA (Deoxyribonucleic Acid) serves as the hereditary material, carrying the entire genetic blueprint for the organism, and it is structured as a double helix. RNA (Ribonucleic Acid) is primarily involved in taking the genetic information encoded in DNA and translating it into proteins, a process that involves different forms like messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Both DNA and RNA are polymers, meaning they are large molecules composed of many repeating subunits, which is the key structural definition of a nucleic acid. Therefore, when asked to identify a nucleic acid from a list of biological molecules, DNA and RNA are the most accurate and fundamental examples.

The incorrect option is 2:

NAD and NADP are not nucleic acids; they are coenzymes that play a vital role in cellular metabolism. NAD stands for Nicotinamide Adenine Dinucleotide, and NADP stands for Nicotinamide Adenine Dinucleotide Phosphate. Their main function is to act as electron carriers, accepting and donating electrons in redox reactions that are central to energy production, such as glycolysis and the Krebs cycle. Although they are structurally derived from nucleotides (specifically incorporating Adenine), their role is transient electron transfer, not the long-term, informational storage or transmission that defines DNA and RNA. They are essential accessories in enzyme-catalyzed reactions, unlike nucleic acids, which are the main informational storage molecules.

The incorrect option is 3:

FMN and FAD are also not classified as nucleic acids but rather as coenzymes, specifically flavoproteins, which are integral to many redox reactions in the cell. FAD (Flavin Adenine Dinucleotide) and FMN (Flavin Mononucleotide) are both derived from Riboflavin, which is Vitamin B2. Like NAD and NADP, they serve as prosthetic groups that are tightly bound to certain enzymes, most famously in the electron transport chain in the mitochondria, where they are critical for cellular respiration. Their function is focused on the transfer of hydrogen atoms and electrons. While FAD does contain an Adenine nucleotide component, its overall structure and function—as a non-polymeric, enzyme-linked electron carrier—clearly place it outside the definition of a nucleic acid.

The incorrect option is 4:

ATP stands for Adenosine Triphosphate, and while its structure is very similar to a single RNA nucleotide (an adenine base, a ribose sugar, and a phosphate group), it is not a nucleic acid. ATP's primary and most crucial biological role is to serve as the energy currency of the cell. It stores and releases energy needed for various cellular activities like muscle contraction, nerve impulse transmission, and active transport. ATP is a monomer, a single molecule, and does not form the vast, continuous polymer chain that is characteristic of nucleic acids like DNA and RNA. Therefore, it is categorized as a high-energy nucleoside triphosphate, an energy molecule, rather than a true nucleic acid.