Structure of Prokaryotic and Eukaryotic Cells

Did you know that a fish, a rose, and an amoeba are all made of the same essential components despite their discrete appearance? From a single-celled organism to a multicellular organism that makes a complex structure, every living organism is made up of cells. Prokaryotic and eukaryotic cells are the two main categories of cells present in living beings. For millions of years, prokaryotes were the only form of life on Earth. It is believed that Eukaryotic cells evolved from prokaryotes. A prokaryotic cell is typically any organism that lacks a distinct nucleus and other organelles due to an absence of internal membranes. Single-celled organisms of the domains Bacteria and Archaea fall into this cell type. Eukaryotes are cells or organisms that possess a clearly defined nucleus surrounded by a nuclear membrane—for example, animal cells, plant cells, fungi, and protists.

The Prokaryotic Cell

Prokaryotic are simple structures, usually unicellular and lack membrane-bound structures. Moreover, the DNA is found in the form of bundles called nucleoids.

The following structures and organelles can be found in a prokaryotic cell, apart from common structures:

1. Nucleoid: Bundles of DNA found in the central region of the cell.

2. Cell wall: The cell wall serves as a structure and protection from the outside environment. Prokaryotes usually have a rigid cell wall made up of peptidoglycans.

3. Capsule: A layer of carbohydrates surrounding the cell wall that helps attach to surfaces.

4. Pili: They are rod-shaped structures involved in DNA transfer and attachment.

5. Flagella: They are thin, hair-like structures that aid in movement.

Prokaryotes are organised into three domains: Eukarya, Bacteria, and Archaeans. Cyanobacteria, a prokaryote, are capable of performing photosynthesis. 

Prokaryotic cells produce clones of themselves through binary fission and rely more on horizontal genetic transfer for their variation.

Binary fission is a simpler and faster process than mitosis and involves DNA replication, chromosomal segregation, and ultimately cell separation into two daughter cells genetically identical to the parent cell. In contrast, mitosis does not involve the nuclear envelope, centromere, and spindle formation.

The Eukaryotic Cell

Eukaryotes are complex organisms with a nucleus and other organelles enclosed in a plasma membrane.

Here are the primary components of eukaryotic cells.

• Nucleolus: The nucleolus is the part of the nucleus where ribosomal RNA is produced.

• Cell wall: The cell wall, also called the cytoskeleton, provides the structure that enables cell division.

• Mitochondria: They are responsible for energy production; hence, they are known as the cell’s powerhouse.

• Endoplasmic reticulum: It plays a role in protein maturation and transportation.

• Vesicles and vacuoles: They are membrane-bound sacs aid in transportation and storage.

Many eukaryotes also have the Golgi apparatus, chloroplasts, and lysosomes.

Most eukaryotes undergo sexual reproduction resulting in offspring with genetic material, a mixture of the parents’ genome. In this process of sexual recombination, genetic variation is generated.

Mitosis is followed by cytokinesis in eukaryotic cells. This is a multi-stage process in which the nuclear membrane disintegrates, and the chromosomes are sorted and divided so that each daughter cell obtains two sets of chromosomes. Cytokinesis occurs when the cytoplasm divides to produce two genetically identical daughter cells.

Parts of Prokaryotic and Eukaryotic Cells and Venn Diagram

Every cell shares a few common features, whether it is a prokaryote or eukaryote. These components include: 

1. Cytoplasm: Comprises the jelly-like fluid in which cellular structures are suspended.

2. Plasma membrane: This membrane encloses the interior of a cell and protects it from its surrounding environment.

3. Ribosomes: These are the factories that synthesise proteins.

4. DNA: A cell’s genetic material.

Difference between Prokaryotes and Eukaryotes

Several differences exist between prokaryotes and eukaryotes, including differences in structure—whether a nucleus exists or not if membrane-bound organelles are present, and molecular variation—whether the DNA is circular or linear. The differences are listed below.

Conclusion

Prokaryotes have a diameter range between 0.1-5.0 µm, which is significantly smaller than eukaryotes (10-100 µm). The smaller size of prokaryotes facilitates the exchange of ions, organic molecules, and waste products in and out of the cell quickly. Whereas in the case of larger eukaryotic cells, several structural adaptations have been evolved to enhance cellular transportation. Therefore, prokaryotes are the earliest and most primitive form of life that evolved into complex eukaryotic cells approximately 1.8 billion years ago. They can be differentiated based on genetic materials enclosed by a nuclear envelope. Prokaryotes do not possess membrane-bound organelles, while eukaryotes do.