Antisense technology is :

Question

Accepted Answer

The correct option is 1: When a piece of RNA that is complementary in sequence is used to stop expression of a specific gene

Antisense technology is a fundamental technique in molecular biology and genetic engineering aimed at controlling gene expression with high specificity. The term itself is derived from the core principle of genetic information flow, known as the Central Dogma: DNA is transcribed into messenger RNA (mRNA), and the mRNA is then translated into a protein. The mRNA molecule is referred to as the 'sense' strand because it contains the protein-coding message. Antisense technology involves introducing a synthetic or naturally occurring single-stranded nucleic acid (typically an RNA molecule or a DNA oligonucleotide) that is perfectly *complementary* to a target mRNA sequence. This complementary strand, known as the 'antisense' molecule, binds to the 'sense' mRNA through standard base-pairing (A-U, G-C) to form a double helix. This resulting RNA duplex effectively acts as a physical block that prevents the cellular machinery, the ribosome, from translating the mRNA into its corresponding protein, thereby "silencing" the gene. This mechanism is crucial for research purposes to understand gene function (gene knockdown) and has proven potential as a therapeutic strategy to treat diseases caused by the overexpression of harmful proteins.

The incorrect option is 2: RNA polymerase that produce DNA

This option fundamentally confuses two different classes of enzymes and the direction of nucleic acid synthesis. **RNA polymerase** is the enzyme responsible for **transcription**, the process of synthesizing RNA from a DNA template (DNA $\to$ RNA). Conversely, the synthesis of DNA from an RNA template (RNA $\to$ DNA) is the unique function of an enzyme called **Reverse Transcriptase**. Reverse Transcriptase is characteristic of retroviruses, such as HIV, which must first convert their RNA genome into a DNA copy before integrating it into the host cell's DNA. Therefore, the function described in this option is not related to RNA polymerase, nor does it define the concept of antisense technology.

The incorrect option is 3: A cell displaying a foreign antigen used for synthesis of antigens

This statement describes key steps in an **adaptive immune response** and is entirely unrelated to gene regulation via nucleic acids. A cell "displaying a foreign antigen" is known as an **Antigen-Presenting Cell (APC)**, such as a B-cell or macrophage, or an infected host cell. The purpose of displaying the antigen (a molecular fragment) on the cell surface via MHC molecules is to alert T-lymphocytes (T-cells) to the presence of a threat. This alert initiates an immune cascade, which leads to the eventual production of antibodies (not antigens) by plasma cells, which are specialized B-cells. This whole process is a complex immunological defense mechanism, not an in-vitro or in-vivo genetic engineering technique.

The incorrect option is 4: Presence of somatoclonal variants in tissue culture

This option describes a phenomenon found exclusively in **plant biotechnology**, specifically plant tissue culture. **Somaclonal variation** refers to the genetic variability (mutations or epigenetic changes) observed among plants that have been regenerated from somatic (non-sexual) cells in culture. This variation arises spontaneously due to stress and genetic instability in the culture conditions. It is a sometimes-undesirable side effect of micropropagation or a sometimes-desired source of new traits for plant breeding. It is a random, unintended occurrence in whole-plant propagation and bears no relation to the targeted, regulatory, and designed molecular mechanism of antisense technology.