Prokaryotic Cell: Definition, Characteristics, Diagram & Structure

Prokaryotic Cell: What is a prokaryotic cell? To know this, first, we should know what a cell is. The cell is the basic unit of life and a cell can be either a prokaryotic cell or eukaryotic cell. We see different types of organisms all around. Can you say which one is made of prokaryotic and which one is of eukaryotic? All organisms which we can see with our naked eyes are eukaryotes whereas the organisms which we cannot be seen with naked eyes but with an aided eye are called prokaryotic. Our body is home to trillions of Prokaryotic Cells. Let’s get into the article to know more about the topic.

Prokaryotic Cell Definition

Prokaryotic cells are single-celled organisms that lacks a true nucleus and other membrane-bound organelles.

What is a Prokaryotic Cell?

1. Prokaryotic cells are microorganisms that are known to be the earliest on earth.
2. Kingdom Monera includes the prokaryotic cells. A teaspoon full of rich soil may contain billions of them.
3. Prokaryotic cell refers to the cell which is unicellular, i.e. made of a single cell.
4. Prokaryotic means “pro” = primitive and “karyos” = nucleus, i.e. prokaryotic cell refers to the cell which has a primitive nucleus.
5. Bacteria and Archaea come under prokaryotes.

Characteristics of Prokaryotic Cell

1. Prokaryotic cells have no organized nucleus, i.e. their genetic material is not surrounded by a nuclear membrane and that type of nucleus is called the nucleoid.
2. The cell is surrounded by a plasma membrane.
3. Surrounding plasma membrane is a cell wall that is usually made of carbohydrates and small proteins.
4. But cell walls of archaea do not have a peptidoglycan layer and have different polysaccharides and proteins. Some of the cell walls are made of polysaccharide pseudomurein.
5. Functions of cell wall-
   • a) Protection
   • b) Maintains the cell shape
   • c) Prevents from dehydration
6. DNA is the genetic material of the cell.
7. Mesosomes are attached to the cell membrane which are responsible for cellular respiration.
8. Plasmids are extrachromosomal (not the part of the main chromosome), double-stranded, circular DNA may be present in the cytoplasm which can self-replicate and is an ideal tool for genetic engineering.
9. Prokaryotic cells are devoid of membrane-bound organelles like mitochondria, endoplasmic reticulum, chloroplasts, and advanced \(9+2\) flagella.
10. These organisms are found everywhere that life can possibly be supported.
11. These cells move by the simple beating of flagella or by gliding.
12. Some of the prokaryotic cells can respire aerobically while some anaerobically.
13. Nutrition can be autotrophic or heterotrophic. Heterotrophic cells can be parasitic, which takes the nutrition from the living host or saprophytic, which takes the nutrition from the dead and decaying matter.
14. Their reproduction is by spore formation or binary fission.

Prokaryotic Cell Diagram

Prokaryotic Cell Structure

All prokaryotic cell shares four common components:-

1. Plasma Membrane– It refers to the outer membrane which separates the inner environment from the external environment. It is a thin lipid bilayer. It is selectively permeable.

2. Cytoplasm– It refers to the fluid found inside the plasma membrane which constitutes a few cell organelles.

3. Genetic Material– Double-stranded and circular DNA is the genetic material that isly suspended in the cytoplasm or attached to the cell membrane at some points without a nuclear covering. The genetic material in the prokaryotic cell can be found as:

a. Nucleoid- It contains all the genes that code for all the proteins of the prokaryotic cell which have structural and functional roles.
b. Plasmid – It may contain genes that code for proteins or enzymes that can protect the cell from toxic substances.

4. Ribosomes– Due to the presence of ribosomes in the cytoplasm, it looks granular. It is involved in protein synthesis. Here ribosomes are of \({\rm{70S}}\) type.

5. Some prokaryotic cells have a slimy layer called capsule outside the cell wall which is made up of polysaccharides (sugar polymers). These capsules help the cell to:

• a) Escape from engulfment by the phagocytic cells
• b) Prevent from drying
• c) Attach to the surfaces
• d) Protect it from injury, high temperature
• e) To protect the cell from our immune response

6. Prokaryotic cells may have flagella used for locomotion and pili for attachment to surfaces or else can be passively transported by wind, water, etc.

7. Pilli can also be used to transfer DNA molecules to other bacteria.

Reproduction in Prokaryotic cell

1. Prokaryotic cell reproduces by both asexual and sexual methods.
2. They reproduce by binary fission, which is an asexual method.

Binary Fission

In this method of reproduction, circular DNA replicates followed by cell expansion. Due to this, the duplicated DNA is pulled apart. Then, there is a constriction in the middle which results in separating the two cells apart from each other, resulting in the formation of two daughter cells.

Prokaryotic cells may reproduce sexually by the conjugation, transformation, and transduction processes.

Conjugation– In this process, genetic material is transferred to the other prokaryotic cell through a sex pilus, formed between two cells as a bridge.

Transformation– In this method, a cell may take genetic material from an outside environment which may get incorporated in its own genetic material or remain as extrachromosomal material called a plasmid.

Transduction– In this method, a bacteriophage inserts DNA (taken from other bacteria) into the bacteria cell.

Prokaryotic Cell Size

Size of a typical prokaryotic cell is \(0.1\) to \(5.0\,{\rm{\mu m}}\) (micrometers). From the given figure we can compare the size of a prokaryotic cell (bacterium in the figure).

Size of an eukaryotic cell ranges from \(10\) to \(100\,{\rm{\mu m}}\). Small size of the prokaryotes help in easy diffusion of ions and organic molecules inside the cell and then to every part of the cell. Small size also helps in easy diffusion of waste materials out of the cell which is not the case of eukaryotic cells in which different intracellular mechanisms have been developed to transport materials inside and outside of the cell.

Prokaryotic Cell Examples

Examples of prokaryotic cells include bacteria, archaea, cyanobacteria (blue-green algae), etc.

1. Bacteria- They belong to Eubacteria (true bacteria). These bacteria are found everywhere.
2. Archaea- They belong to Archaea. These are found in extreme conditions. For example, halophiles which are found in extreme salty environments, thermophiles, found in high temperatures, etc.
3. Cyanobacteria, also named as the blue green algae, because of the presence of chlorophyll in it. Due to which, it can photosynthesize. These are eco-friendly as they are involved in the liberation of oxygen to the environment. A huge amount of oxygen is supplied by them.

Summary

Prokaryotic cells are the unicellular cells that lack a well-defined nucleus, i.e. genetic material is not enclosed by a nuclear membrane. These cells are very minute in size \(0.1\) to \(5.0\,{\rm{\mu m}}\). Common prokaryotic cell is a bacterial cell. Our body has over \(100\) trillion bacterial cells. These simple cells can thrive well everywhere and even in extreme conditions.

Frequently Asked Questions (FAQs) on Prokaryotic Cell

Q.1. What is a prokaryotic cell simple definition?
Ans: Prokaryotic cell refers to the unicellular cell which lacks a well-defined nucleus and other membrane-bound organelles.

Q.2. What is the difference between prokaryotic and eukaryotic cells?
Ans: The difference between prokaryotic and eukaryotic cells are as follows:

Q.3. What are 4 examples of prokaryotic cells?
Ans: Examples of prokaryotic cells are: bacterial cells like Escherichia Coli Bacterium, Streptococcus Bacterium, Cyanobacteria, Archaea, Mycoplasma, etc.

Q.4. Which are prokaryotes?
Ans: Prokaryotes refers to unicellular organisms lacking a well-defined nucleus and other membrane-bound organelles.

Q.5. What are 2 examples of prokaryotic cells?
Ans: Examples of prokaryotic cells are Bacteria and cyanobacteria.

Q.6. What is a prokaryotic cell example?
Ans: An example of a prokaryotic cell is a bacterial cell.

Learn about Prokaryotic Organisms Here

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