Prokaryotic and Eukaryotic Cells: Structure, Features and Differences
What is a Prokaryotic Cell?
Prokaryotic cells are small, simple and primitive cells that were among the earliest forms of life on Earth.
They are commonly found in bacteria such as Mycoplasma and Cyanobacteria.
Unlike eukaryotic cells, prokaryotes lack a true nucleus and membrane-bound organelles.
General Features of Prokaryotic Cells
- Small and simple structure.
- No true nucleus.
- No membrane-bound organelles.
- Single circular DNA molecule.
- Rapid reproduction by binary fission.
- 70S ribosomes present.
Capsule (Glycocalyx)
Many bacteria possess an outer protective covering called the capsule or glycocalyx.
- Made mainly of polysaccharides.
- Protects against desiccation.
- Provides defense against host immunity.
- Helps bacterial attachment.
Cell Wall
The bacterial cell wall surrounds the plasma membrane and provides shape and rigidity.
It is composed mainly of peptidoglycan along with other substances depending on the bacterial type.
Gram Positive vs Gram Negative Bacteria
| Feature | Gram Positive | Gram Negative |
|---|---|---|
| Cell Wall | Thick | Thin |
| Staining Color | Violet/Purple | Red/Pink |
| Examples | Lactobacillus, Clostridium | E. coli, Rhizobium |
Plasma Membrane
The plasma membrane is the innermost phospholipid bilayer enclosing the cytoplasm.
Functions
- DNA replication support.
- Septum formation during binary fission.
- Cellular respiration.
- Transport of substances.
DNA (Nucleoid)
The genetic material of bacteria consists of double-stranded DNA arranged in a nucleoid region.
Unlike eukaryotes, the DNA is not enclosed within a nuclear membrane.
Polysomes
Polysomes are clusters of ribosomes attached to a single mRNA molecule.
They increase the efficiency of protein synthesis in bacterial cells.
Fimbriae or Pili
Fimbriae and pili are hair-like projections extending from the bacterial surface.
- Help in attachment.
- Assist in conjugation.
- Enable genetic transfer.
Flagella
Flagella are locomotory structures that help bacteria move toward nutrients and respond to environmental stimuli.
What is a Eukaryotic Cell?
Eukaryotic cells are true cells found in plants, animals, fungi and protists.
- Possess a true nucleus.
- Contain membrane-bound organelles.
- Generally larger than prokaryotic cells.
- Have linear chromosomes.
Difference Between Prokaryotic and Eukaryotic Cells
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Nucleus | Absent | Present |
| DNA | Circular | Linear |
| Organelles | Absent | Present |
| Ribosomes | 70S | 80S |
| Cell Size | Small | Large |
| Cell Division | Binary Fission | Mitosis/Meiosis |
Frequently Asked Questions
What is a prokaryotic cell?
A primitive cell lacking a true nucleus and membrane-bound organelles.
What is a eukaryotic cell?
A cell containing a true nucleus and membrane-bound organelles.
What are examples of prokaryotes?
Bacteria, Cyanobacteria and Mycoplasma.
Which ribosomes are found in prokaryotes?
70S ribosomes.