Prokaryotic Cells

Cells were long believed to have a well-defined structure with a nucleus, but in the 1870s, this perspective began to shift. Observations of simpler, nucleus-free cells challenged this traditional view of cells, leading to the classification of these cells in a completely new type — the prokaryotic cells. The discovery of prokaryotic cells—small, primitive, and without membrane-bound organelles—reshaped cell theory and opened the door to the study of microbiology, revealing that life could exist in far simpler forms than once imagined.

1.0What are Cells?

Cells are the building blocks of life—small biological units with the capability to undertake all functions required by living organisms, e.g., reproduction, processing of energy, and reaction to stimuli. All living organisms, ranging from the simplest bacterium to the most intricate plant or animal, consist of cells. 

Based on the presence of a true nucleus and membrane-bound organelles, cells are broadly classified into two types: 

• Prokaryotic Cells
• Eukaryotic Cells

Here, we will predominantly explore prokaryotic cells along with their comparison with their counterparts. 

2.0Introduction to Prokaryotic Cells 

Prokaryotic cells are the most ancient and primitive types of cells that lack a true nucleus and membrane-bound organelles. The word prokaryotic itself comes from the combination of the Greek words pro, which means before, and karyon, meaning nucleus. 

Thus, a prokaryotic cell is defined as a cell that existed before the evolution of the nucleus, which is why we call it the first or the most primitive life form on Earth. The first evidence of these cells dates back over 3.5 billion years. 

Though simpler in structure than their counterpart, “eukaryotic cells”, these cells are highly capable of surviving the most diverse environments. That is, prokaryotic cells can survive high temperatures, deep ocean vents, and even the arctic ice. 

Some of the most famous examples of prokaryotic cells include all the species of bacteria, such as Escherichia coli (E. coli), found in the intestines, and Streptococcus, which can cause a sore throat. 

3.0Prokaryotic Cell Structure

Prokaryotic cell structure is predominantly composed of a structure similar to classical cells, however, without membranes. Which include: 

1. Cell Wall: Like plant cells, prokaryotic cells also have a cell wall, which provides them with their shape and rigidity. The cell wall in these cells is generally composed of peptidoglycan. 
2. Plasma/Cell Membrane: The Cell membrane in a prokaryotic cell, just like classical ones, facilitates the controlled movement of substances into and out of the cells. 
3. Cytoplasm: It is the jelly-like substance where all the organelles, and in this case, non-membranous, are present. Also, all the metabolic reactions occur in this region. 
4. Nucleoid: Nucleus, when not bound with a nuclear membrane like in classical cells, is known as nucleoid. It is the region where the genetic material, the DNA, of a prokaryotic cell is present. 
5. Plasmids: These are the small, circular DNA fragments present in the cytoplasm of prokaryotic cells. Unlike nuclear DNA, these fragments aren’t involved in reproduction. 
6. Ribosomes: These are the site of protein synthesis in any type of cell, including prokaryotic ones. 
7. Optional Components: Apart from these classical components, prokaryotic cells also contain some extra parts for locomotion or protection. These parts may include flagella, pilus/fimbriae, or a capsule. 

Unlike eukaryotic cells, prokaryotic cells do not contain any membrane-bound cell organelles, like endoplasmic reticulum, lysosomes, vacuoles, Golgi apparatus, or mitochondria. 

4.0Characteristics of Prokaryotic Cells

The prokaryotic cells possess some exceptional characteristics, helping them not just exist but thrive in extreme environments. These features include:

• Lack of a True Nucleus: DNA is not bound within a membrane but resides in the nucleoid area.
• No Membrane-Bound Organelles: Mitochondria, endoplasmic reticulum, and Golgi bodies are not present.
• Simple Structure: These cells possess a simple structure but are nevertheless able to perform all functions of life.
• Unicellular: Prokaryotes are typically single cells.
• Binary Fission: Asexual reproduction of prokaryotes occurs by binary fission—a method by which the cell splits into two identical daughter cells.
• Presence of Cell Wall: A majority of prokaryotes possess a robust cell wall for protection and structural support.
• Smaller Ribosomes (70S): Their ribosomes are smaller compared to eukaryotic cells (80S ribosomes).
• Extra DNA Components (Plasmids): Prokaryotes possess plasmids—additional DNA entities that usually confer survival benefits, such as resistance to antibiotics.

5.0Importance of Prokaryotic Cells

Although simple, prokaryotic cells play a vital role in sustaining ecosystems and human life. Here is why they’re important: 

1. Environmental Roles: Bacteria are responsible for breaking down the organic matter of dead organisms and recycling nutrients. These are also useful in nitrogen fixation in soil. 
2. Industrial Use: Bacteria are used on an industrial level for fermentation to make edibles, such as yoghurt, cheese, and vinegar. 
3. Medical Applications: Antibiotics used to fight disorders in the human body are also produced by bacterial species. 
4. Research and Biotechnology: Owing to their simpler structure, prokaryotic cells are also used for cell modelling and genetic studies of modified cells. 

6.0Prokaryotic vs Eukaryotic Cells