Differences between Eukaryotic and Prokaryotic cells

Classification of Microorganisms:

Microbes are widely spread in an environment where some are responsible for serious harm and some are beneficial to life. They are classified into six major groups: bacteria, archaea, fungi, protozoa, algae, and viruses. All these microorganisms broadly belong to two groups: cellular (prokaryotic and eukaryotic) and acellular.

(a) Acellular organisms: These are microorganisms that have neither cells nor cell membranes. They are composed of a few genes protected by a protein coat. Outside of the host, they act as dead, but inside the host, they are alive and reproduce. An example is viruses.

(b) Cellular organisms: These are the microorganisms that have definite cell structures. Based on the cellular structure they are further divided into prokaryotic and eukaryotic. Prokaryotes are cells without a nucleus and have no membrane-bound organelles. They are less complex in structures. Examples: Bacteria and Archaea.

A. Bacteria:

(singular: Bacterium) (study of bacteria: bacteriology)

1. They are prokaryotic and unicellular

2. The size is 1/1000 the volume of a typical eukaryotic cell.

3. Mainly two groups of bacteria are: (a) Archaeobacteria: Ancient bacteria. (b) Eubacteria: True bacteria.

4. They are in various shapes likely bacillus (rod), coccus (spherical), spirillum (spiral), and vibrio (curved rod).

5. They are motile or non-motile.

6. They obtain their energy from the sun as well as from organic and inorganic molecules, and as per that they are classified as: Photosynthetic autotrophs (use energy from the sun to produce their own carbohydrates for energy), Chemosynthetic autotrophs (process inorganic molecules for energy (example: sulfur or iron) and heterotrophs (depend on outside sources of organic molecules (example: carbohydrates or sugars) for energy.

7. Optimum temperature: −20^oC to 110^oC (freezing is 0^oC and boiling is 100^oC).

B. Algae:

1. They are eukaryotic, unicellular, or multicellular.

2. They are microscopic and macroscopic in size.

3. They are motile or non-motile.

4. They obtain their energy from photosynthetic autotrophs.

C. Fungi:

1. They are eukaryotic.

2. They are unicellular or multicellular (yeasts are unicellular, molds are multicellular).

3. They are non-motile.

4. They obtain their energy from outside sources of organic molecules.

5. They act as scavengers, they live off dead matter and thus, decompose it.

D. Protozoa:

1. They are eukaryotic.

2. They are unicellular.

3. They are motile or non-motile.

4. They obtain energy from outside sources of organic molecules.

E. Viruses:

1. They are acellular and obligate intracellular parasites.

2. Structure of a virus: A piece of nucleic acid (RNA or DNA) enclosed by a protein coat (capsid); possess no nucleus, organelles, cell membrane, or cytoplasm.

3. Size - 1/10 to 1/1000 the size of an ordinary bacterial cell.

4. They are non-motile.

Thereafter the differences between the eukaryotic and prokaryotic cells are depicted in Table.

Differences between Eukaryotic and Prokaryotic cells

Cells are the basic structural and functional units of life, classified into eukaryotic and prokaryotic based on their complexity and organization. Below are the key differences between these two cell types:

1. Nucleus:

Eukaryotic cells: Have a well-defined nucleus enclosed by a nuclear membrane.

Prokaryotic cells: Lack a nucleus; the genetic material is free-floating in the cytoplasm.

2. Chromosomes:

Eukaryotic cells: Contain multiple linear chromosomes.

Prokaryotic cells: Usually have a single circular chromosome, often accompanied by plasmids.

3. Cell Type:

Eukaryotic cells: Usually multicellular (e.g., plants and animals).

Prokaryotic cells: Mostly unicellular (e.g., bacteria and archaea).

4. Lysosomes and Microtubules:

Eukaryotic cells: Contain lysosomes and microtubules for cellular digestion and structural support.

Prokaryotic cells: Lack of both lysosomes and microtubules.

5. Genetic Recombination:

Eukaryotic cells: Undergo meiosis and gamete fusion for genetic recombination.

Prokaryotic cells: Exchange DNA through a unidirectional process like conjugation.

6. Endoplasmic Reticulum and Golgi Apparatus:

Eukaryotic cells: Have both organelles for protein and lipid processing.

Prokaryotic cells: Do not have these organelles.

7. Mitochondria:

Eukaryotic cells: Have mitochondria for energy production.

Prokaryotic cells: Lack mitochondria; energy production occurs in the cell membrane.

8. Ribosomes:

Eukaryotic cells: Contain larger ribosomes (80S).

Prokaryotic cells: Contain smaller ribosomes (70S).

9. Flagella:

Eukaryotic cells: Flagella are microscopic and membrane-bound.

Prokaryotic cells: Flagella are simpler, and composed of a single fiber.

10. Cell Size:

Eukaryotic cells: Larger in size (10-100 µm).

Prokaryotic cells: Smaller in size (1-10 µm).

11. Vacuoles:

Eukaryotic cells: Large vacuoles, especially in plant cells.

Prokaryotic cells: Small vacuoles, if present.

12. Nuclear Membrane:

Eukaryotic cells: Have a selective nuclear membrane.

Prokaryotic cells: The nuclear membrane is absent.

Examples:

Eukaryotic cells: Found in plants, animals, fungi, and protists.

Prokaryotic cells: Found in bacteria and archaea.

Organelles	Eukaryotic Cell	Prokaryotic Cell
Nucleus	Present	Absent
Chromosome	More than one	One (Plasmid)
Cell type	Usually, multicellular	Usually, unicellular
Lysosomes	Present	Absent
Microtubules	Present	Absent
Genetic recombination	Meiosis and fusion of gamates	Undirectional transfer of DNA
Endoplasmic reticulum	Present	Absent
Mitochondria	Present	Absent
Ribosome	Larger	Smaller
Golgi apparatus	Present	Absent
Flagella	Microscopic in size; membrane-bound	Submicroscopic in size, composed of only one fiber
Cell size	10-100 µm	1-10 µm
Vacuoles	Present in large size	Present in small size
Nuclear membrane	Selective	Not present
Examples	Animal and Plants	Bacteria and Archaea

General Classification of Bacteria:

A. Based on the wall structure: Gram Positive (Staphylococcus, Streptococcus, Clostridium, Bacillus), Gram-negative (E. coli), Acid-fast (Mycobacterium), Wall-less (Mycoplasma).

B. Unusual: Obligate intracellular (Rickettsia, Chlamydia).

C. Cell morphology:

1. Shapes (Rod, Cocci, Spiral)

2. Associations (Individual, Diplococci, Staphylococci, Streptococci).

D. Growth characteristics:

1. Oxygen requirement (Aerobic, Anaerobic, Microaerophilic, aerotolerant, Facultative)

2. Spore formation

3. Intracellular/extracellular

4. Fastidious/non-fastidious