Prokaryotic and Eukaryotic Cells – Introduction, Diagrams and Differences

The Biology Topics of biotechnology involve using living organisms to develop new products or solve problems.

Difference between Prokaryotic and Eukaryotic Cells and Nucleus and Nucleoid

All living organisms present on Earth can be classified into the following two types:

• Non-cellular organisms that do not contain any cell in their body organization, e.g., viruses.
• Viruses lack any membrane and hence do not show characteristics of life until they enter a living body (i.e., prokaryotic cell or eukaryotic cell) to use its cell machinery to reproduce.
• Cellular organisms contain either one or many cells in their bodies, e.g., bacteria, plants, and animals.

Cellular organisms are again divided into the following two main types:
(a) Prokaryotes:
These organisms have primitive and incomplete cells. Thus, they contain prokaryotic cells in their body structure. Prokaryotic cells have all three basic structures of a typical cell but lack nuclear membranes around their genetic substances (DNA).

The nuclear material of a prokaryotic cell consists of a single chromosome that is in direct contact with the cytoplasm. Here the undefined nuclear region in the cytoplasm is called a nucleoid, i.e., there is no nuclear membrane. In a prokaryotic cell other membrane-bound organelles, such as mitochondria, are also absent. Ribosomes, however, are present in prokaryotic cells. The prokaryotes include archaebacteria, bacteria, and cyanobacteria (which were earlier called blue-green algae).

(b) Eukaryotes:
These have advanced and complete cells. These cells contain membrane-bound nuclei and other cellular organelles and are called eukaryotic cells. Such cells are found in unicellular and multicellular plants and animals and contain plasma membranes, nuclei, DNA, and cytoplasm with ribosomes and cellular organelles such as mitochondria. The differences between prokaryotic cells and eukaryotic cells are given in Table.

Differences between Prokaryotic Cells and Eukaryotic Cells

Prokaryotic Cell	Eukaryotic Cell
1. Size of a cell is generally small (1-10 mm).	1. Size of a cell is generally large (5-100 mm).
2. Nucleus is absent (Nuclear region or nucleoid is not surrounded by a nuclear membrane).	2. Nucleus is present (Nuclear material is surrounded by a nuclear membrane).
3. It contains a single chromosome.	3. It contains more than one chromosome.
4. Nucleolus is absent.	4. Nucleolus is present.
5. Membrane-bound cell organelles are absent.	5. Membrane-bound cell organelles such as mitochondria, plastids, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, etc., are present.
6. Cell division takes place by fission or budding (no mitosis).	6. Cell division occurs by mitotic or meiotic cell division.

Differences between Nucleus and Nucleoid

Nucleus	Nucleoid
1. It is larger in size.	1. It is comparatively smaller in size.
2. It has a covering of a double membrane envelope.	2. A covering membrane is absent. It lies free in the cytoplasm.
3. Nucleolus is present in it.	3. Nucleolus is absent in it.
4. Its DNA content is equal to two or several DNA molecules.	4. Its DNA content is equal to a single DNA molecule.
5. Its DNA is associated with histone proteins to form chromatin.	5. In it histones are absent. DNA of a nucleoid is often naked.