Problem 24 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which of the following statements is not true about RNA? [Main April 12, 2019 (I)] (a) It controls the synthesis of protein. (b) It has always double stranded helix structure. (c) It usually does not replicate. (d) It is present in the nucleus of the cell.

Step-by-Step Solution

Answer

The incorrect statement is (b): RNA is typically not double-stranded.

Step 1: Analyze Option (a)

Option (a) states that RNA controls the synthesis of protein. This statement is true because messenger RNA (mRNA) is critical in translating genetic information into proteins during the process of translation.

Step 2: Analyze Option (b)

Option (b) claims RNA always has a double-stranded helix structure. This is false because RNA is typically single-stranded. While there are exceptions like certain types of RNA that can form double-stranded structures temporarily or under specific conditions, most RNA, e.g., mRNA, transfer RNA (tRNA), and ribosomal RNA (rRNA), are primarily single-stranded.

Step 3: Analyze Option (c)

Option (c) asserts that RNA usually does not replicate. This is true. While some viruses replicate their RNA, in most cellular processes, RNA does not self-replicate; rather, it is transcribed from DNA.

Step 4: Analyze Option (d)

Option (d) indicates that RNA is present in the nucleus of the cell, which is true. RNA is transcribed from DNA in the cell nucleus before it migrates to the cytoplasm for translation into proteins.

Key Concepts

Protein Synthesis

RNA plays a vital role in protein synthesis, a process essential for cell function and growth. During protein synthesis, RNA acts as a messenger, carrying genetic instructions from DNA to the ribosome, where proteins are formed. There are key types of RNA involved in this process:

• Messenger RNA (mRNA): Transcribes genetic information from DNA and conveys it to ribosomes.
• Transfer RNA (tRNA): Delivers the appropriate amino acids to the ribosome for protein assembly.
• Ribosomal RNA (rRNA): Combines with proteins to form ribosomes, the sites of protein synthesis in cells.

Each type of RNA contributes uniquely to the translation of genetic codes into functional proteins, facilitating cellular processes and maintaining life.

Nucleic Acids

Nucleic acids, such as DNA and RNA, are biomolecules crucial for storing and transmitting genetic information. These acids are polymers made up of nucleotide monomers. Nucleotides consist of three components: a nitrogenous base, a sugar molecule, and a phosphate group.

There are two main types of nucleic acids:

• Deoxyribonucleic Acid (DNA): Contains the genetic blueprint of a cell and remains primarily double-stranded.
• Ribonucleic Acid (RNA): Involved in protein synthesis and is usually single-stranded.

Nucleic acids hold the instructions needed for the growth, development, and reproduction of all living organisms, making them integral to life.

RNA Replication

RNA replication is a process less commonly observed compared to DNA replication. In many organisms, RNA is transcribed from DNA and does not self-replicate. However, exceptions to this rule exist, particularly among some viruses.

For example:

• Certain RNA viruses can replicate their RNA genome independently, without a DNA intermediate. This means the viral RNA acts as a template for generating new RNA molecules.

This unique capability is critical for the propagation of RNA viruses and sets it apart from cellular RNA, which typically follows the transcription from DNA, not replication route.

Single-Stranded Structure

Typically, RNA exists in a single-stranded form, in contrast to the double-helix structure of DNA. This single-stranded characteristic allows RNA to be more flexible and versatile in its functions.

Here are some benefits of this structure:

• Flexibility: The single-stranded nature allows RNA to fold into complex three-dimensional shapes tailored for its specific roles in the cell, such as catalysis and regulation.
• Functional Diversity: Being single-stranded, RNA can engage in interactions with other molecules like proteins and other RNAs, enhancing its regulatory and functional scope.

Though primarily single-stranded, certain RNA molecules can form intricate secondary structures, including loops and bulges, which are essential for their biological functions.