Nissel's granules are madeup of:

Question

Accepted Answer

The correct option is 2: RNA and Ribosomes

Nissl's granules, also known as Nissl bodies or tigroid substance, are unique and prominent basophilic (base-loving) masses found specifically within the perikaryon (cell body) and the dendrites of neurons. They were discovered by Franz Nissl using basic aniline stains, which is why they appear blue-purple under a microscope. Structurally and functionally, Nissl's granules represent large aggregates of the **Rough Endoplasmic Reticulum (RER)** and numerous free **ribosomes**. The RER is a vast network of membranes studded with ribosomes, which are macromolecular complexes made of ribosomal RNA (**rRNA**) and protein. The presence of these components highlights the granule's paramount function: the massive synthesis of proteins, which is essential for maintaining the large volume and high metabolic demand of the neuron, especially for producing neurotransmitters, enzymes, and structural components. Therefore, the granules are rich in both RNA (from the ribosomes and messenger RNA) and the associated proteins, making this the correct and defining combination of their biochemical constituents.

The incorrect option is 1: DNA and Protein

This option is incorrect because the primary genetic material, **DNA**, is housed almost exclusively within the cell nucleus and is therefore physically separated from the Nissl granules. Nissl's granules are cytoplasmic organelles, specifically the rough endoplasmic reticulum and associated ribosomes, not nuclear structures. While proteins are indeed a major component of the granules, serving as structural parts of the RER and ribosomes, the inclusion of DNA fundamentally misrepresents the granules' composition and their location within the cell. The purpose of the granules is protein synthesis based on genetic instructions, not the storage of the genetic code itself.

The incorrect option is 3: DNA and Cholesterol

This option incorrectly pairs the nuclear component **DNA** with a cell membrane lipid, **Cholesterol**. As previously established, DNA is not a structural part of the cytoplasmic Nissl's granules. Furthermore, while cholesterol is an essential lipid component of all eukaryotic cell membranes, including the membranes of the RER, it is not a primary or defining chemical feature that gives the Nissl granules their characteristic staining properties. The granules are defined by their high concentration of the protein-synthesizing machinery. This combination mistakenly includes two molecules that are either in the wrong location (DNA) or not the main substance responsible for the granule's identity (Cholesterol).

The incorrect option is 4: Thymine and DNA

This description is chemically inaccurate and structurally incomplete for describing the organelle. **Thymine** is a nitrogenous base found exclusively in DNA, not RNA, and since DNA is in the nucleus, this component is not found in the cytoplasmic granules. Moreover, the ribosomes within the granules contain **ribosomal RNA (rRNA)**, which uses the base **Uracil** instead of Thymine. The entire granule complex is composed of far more than just a single base and DNA; it is a complex of RER and ribosomes. This option confuses the building blocks of nucleic acids and mislocates DNA, failing to capture the correct composition of the protein-synthesizing machinery.