**Nucleolus Absence in Prokaryotes**

**Introduction to Prokaryotes and Nucleolus**
Prokaryotes are single-celled organisms that lack a nucleus and membrane-bound organelles. They are classified into two domains: Bacteria and Archaea. On the other hand, eukaryotes, including plants, animals, fungi, and protists, have a well-defined nucleus and various membrane-bound organelles. One of the important organelles found in the nucleus of eukaryotic cells is the nucleolus.

**Definition and Function of Nucleolus**
The nucleolus is a distinct substructure located within the nucleus of eukaryotic cells. It is composed of proteins, RNA, and DNA. The primary function of the nucleolus is to synthesize and assemble ribosomes, which are responsible for protein synthesis. It plays a vital role in cell growth, proliferation, and cellular metabolism.

**Comparison of Prokaryotic and Eukaryotic Cells**
Prokaryotic cells lack a true nucleus and other membrane-bound organelles, which are characteristic of eukaryotes. Instead, their DNA is present in a region called the nucleoid, which is not enclosed by a nuclear membrane. Prokaryotes have a simpler internal structure compared to eukaryotes.

**Absence of Nucleolus in Prokaryotes**
The nucleolus is absent in prokaryotes. Here are the reasons why:

1. **Lack of Nuclear Membrane**: Prokaryotes lack a nuclear membrane, so their DNA is not enclosed in a separate compartment within the cell. Instead, the DNA is present as a single circular chromosome in the nucleoid region. This lack of membrane-bound nucleus means that prokaryotes do not have a defined nucleolus.

2. **Different Ribosome Structure**: Prokaryotes have smaller ribosomes compared to eukaryotes. Prokaryotic ribosomes are composed of different types of RNA and proteins. The assembly of prokaryotic ribosomes occurs in the cytoplasm, not within a nucleolus.

3. **Simpler Cellular Structure**: Prokaryotes have a simpler cellular structure overall. They lack many of the membrane-bound organelles found in eukaryotes, including the nucleus and nucleolus. The absence of a nucleolus in prokaryotes is consistent with their more primitive and simpler organization.

In conclusion, the absence of a nucleolus in prokaryotes is primarily due to their lack of a nuclear membrane, different ribosome structure, and simpler cellular organization. These factors contribute to the distinct differences between prokaryotic and eukaryotic cells.

What are prokaryotic cells (also known as prokaryotes)?
Prokaryotes are simple, small (1-10 µ in size) and primitive type of cells. Prokaryotic cells consist of no ‘well defined nucleus’ and the genetic material is found scattered within the cytoplasm of cell, called nucleoid. These cells do not have membrane bound cell organelles such as mitochondria, Golgi bodies, lysosomes, peroxisomes, ER, etc. All bacteria are prokaryotes, Escherichia coli is the best known prokaryote.
Since, prokaryotes do not have nucleus, they don't have nucleolus.