Prokaryotic Cells: Discovery, Structure, Functions, and Features

Explore the fascinating world of prokaryotic cells and uncover their discovery, structure, functions, and features.

Prokaryotic Cell Definition

“Prokaryotic cells are the cells that do not have a true nucleus and membrane-bound organelles.”

Read More: Cells the Unit of Life Complete Overview for Competitive Exam

What is a Prokaryotic Cell?

• Prokaryotic cells are tiny living things made up of just one cell.

• They’re the oldest life forms on Earth.

• Prokaryotes include Bacteria and Archaea.

• Some prokaryotes, like cyanobacteria, can do photosynthesis.

• In a prokaryotic cell, everything happens inside a single membrane in the cytoplasm.

• These cells can live on their own or as parasites.

Characteristics of Prokaryotic Cell

Prokaryotic cells have some distinct features. Here’s a breakdown:

• No Nuclear Membrane: They don’t have a protective layer around their genetic material.

• Absence of Key Structures: Mitochondria, Golgi bodies, chloroplasts, and lysosomes are not found in these cells.

• Single Chromosome: The genetic material is all packed into a single chromosome.

• No Histone Proteins: Unlike eukaryotic cells, prokaryotic cells lack histone proteins, which are vital components of chromosomes.

• Carbohydrate and Amino Acid Cell Wall: Their cell walls are composed of carbohydrates and amino acids.

• Mitochondrial Role: The plasma membrane serves a role similar to the mitochondrial membrane by carrying respiratory enzymes.

• Asexual Reproduction: They reproduce by splitting in two through a process called binary fission.

• Conjugation for Sexual Reproduction: When it comes to sexual reproduction, they engage in a process called conjugation.

Prokaryotic Cell Structure

A prokaryotic cell is different from eukaryotic cells because it doesn’t have a nuclear membrane. Instead, its genetic material is in a region called the nucleoid within the cytoplasm. These cells can be round, rod-shaped, or spiral.

The main structure of a prokaryotic cell includes:

• Capsule: This is an outer layer that protects the cell, retains moisture and helps in attachment to surfaces and nutrients.

• Cell Wall: It’s the outermost layer that gives shape to the cell.

• Cytoplasm: This gel-like substance contains enzymes, salts, and cell organelles.

• Cell Membrane: Surrounding the cytoplasm, it controls the entry and exit of substances in the cell.

• Pili: These hair-like structures attach to the surface of other bacterial cells.

• Flagella: Long whip-like structures that aid in the cell’s movement.

• Ribosomes: Essential for protein synthesis.

• Plasmids: These are extra pieces of DNA not involved in reproduction.

• Nucleoid Region: The part of the cytoplasm where genetic material is located.

Prokaryotic cells lack certain organelles like mitochondria, endoplasmic reticulum, and Golgi bodies.

Prokaryotic Cell vs Eukaryotic Cells Diagram

The diagram of a prokaryotic cell shows a bacterial cell. It highlights the key feature of not having a true nucleus, which sets it apart from eukaryotic cells. Additionally, the presence of a flagellum is depicted, aiding in distinguishing it from eukaryotic cells.

Components of Prokaryotic Cells

Prokaryotic cells consist of four main parts:

• Plasma Membrane: This outer layer made of phospholipid molecules acts as a protective cover, separating the cell from its surroundings.

• Cytoplasm: A jelly-like substance inside the cell where all the cell’s organelles are suspended.

• DNA: The genetic material of the cell, often in a circular form. It guides the production of proteins and regulates the cell’s activities.

• Ribosomes: These are where protein synthesis takes place.

Read More: Structure and Function of Nucleus: Biology Notes for Competitive Exam

Reproduction in Prokaryotes

Prokaryotes reproduce in two ways:

Asexual Reproduction – Binary Fission

• The organism’s DNA duplicates, and the copies attach to the cell membrane.
• The cell wall expands and moves inward.
• A new cell wall forms between each DNA, splitting the cell into two daughter cells.

Sexual Reproduction – Recombination

This involves the transfer of genes between bacteria and occurs in three ways: conjugation, transformation, and transduction.

• Conjugation: Genes move between two bacteria through a protein tube called a pilus.

• Transformation: The bacterial cell takes DNA from its surroundings and incorporates it into its own DNA.

• Transduction: Genetic material is transferred into the bacterial cell with the help of viruses, particularly bacteriophages.

Examples of Prokaryotic Cells

Bacterial Cells

• Found everywhere on Earth, from soil to the human body.
• Come in various shapes and structures.
• The cell wall, made of peptidoglycan, gives them structure.
• Unique structures include pili, flagella, and a capsule.
• Possess extrachromosomal DNA called plasmids.
• Can form tough, dormant structures known as endospores, helping them survive tough conditions and becoming active again when conditions improve.

Archaeal Cells

• Similar to bacteria in being unicellular and found in diverse environments.
• Common in extreme places like hot springs, as well as in soil, marshes, and even inside humans.
• Have a cell wall and flagella, but their cell wall lacks peptidoglycan.
• Membranes have different lipids with unique stereochemistry.
• Like bacteria, archaea have a single circular chromosome and possess plasmids.

Frequently Asked Questions

Q1. What are the structural features of prokaryotic cells?

The prokaryotic cell is composed of:

• Cell wall
• Cell membrane
• Capsule
• Pili
• Flagella
• Ribosomes
• Plasmids

Q2. How is the prokaryotic cell structure different from that of the eukaryotic cell?

Differences Between Prokaryotic and Eukaryotic Cells:

Prokaryotic Cells:

• Lack of a true nucleus; the nucleus is without a membrane.
• Do not have mitochondria or chloroplasts.

Eukaryotic Cells:

• Have a true nucleus enclosed by a nuclear membrane.
• Possess mitochondria and chloroplasts.

Q3. How does a prokaryotic cell divide?

Asexual Reproduction in Prokaryotic Cells:

• Prokaryotic cells reproduce asexually.
• The most common method is binary fission.
• In binary fission, the cell splits into two, forming two daughter cells.

This simple process is a key aspect of prokaryotic cell reproduction.

Q4. Why is the process of cell division in prokaryotic cells different from that in eukaryotes?

The following differences highlight the simplicity of prokaryotic cells in comparison to eukaryotic cells.

• Prokaryotic cells are simpler than eukaryotic cells.
• They lack a nuclear membrane around their DNA.
• Consequently, cell division in prokaryotic cells is different from that in eukaryotic cells.

Q5. When did the prokaryotic cells evolve?

Evolution of Cells:

• The first prokaryotic cells emerged approximately 3.5 billion years ago.
• Eukaryotic cells, considered to have evolved from prokaryotic cells, appeared later in the evolutionary timeline.

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