Prokaryotic and Eukaryotic Microbes

Microorganisms are classified into two major groups based on their cellular structure: Prokaryotes and Eukaryotes. These groups differ in complexity, structure, and the presence of specialized organelles.

A. Prokaryotic Microorganisms

• Definition: Prokaryotes are simple, unicellular organisms that lack a true nucleus and membrane-bound organelles.
• Examples: Bacteria and Archaea.

Characteristics:

Cellular Organization:

• Cell walls are composed of peptidoglycan in bacteria (absent in Archaea).
• Lack membrane-bound organelles such as mitochondria, Golgi bodies, and endoplasmic reticulum.
• Ribosomes: Small (70S type) and scattered in the cytoplasm.
• Flagella, when present, are composed of a single protein called flagellin.

Genetic Material:

• DNA is circular, double-stranded, and not enclosed in a nuclear membrane.
• DNA is associated with histone-like proteins but lacks true histones.
• May possess plasmids (small, circular DNA) as extra-chromosomal elements.

Energy Metabolism:

• Energy production occurs in the cytoplasmic membrane.
• Photosynthetic prokaryotes (e.g., cyanobacteria) use internal membrane systems for photosynthesis.

Reproduction:

• Reproduce asexually through binary fission.
• Exchange genetic material via processes like conjugation, transduction, and transformation.

B. Eukaryotic Microorganisms

• Definition: Eukaryotes are more complex, and their cells contain a nucleus and various membrane-bound organelles.
• Examples: Fungi, protozoa, algae, and helminths (parasitic worms).

Characteristics:

Cellular Organization:

• Cell walls are composed of cellulose (in algae) or chitin (in fungi).
• Possess membrane-bound organelles, such as mitochondria, chloroplasts (in photosynthetic organisms), Golgi apparatus, and endoplasmic reticulum.
• Ribosomes: Larger (80S type) except for mitochondrial and chloroplast ribosomes, which are 70S.
• Flagella, when present, have a complex 9+2 arrangement of microtubules.

Genetic Material:

• DNA is linear and enclosed within a nuclear membrane.
• DNA is complexed with histone proteins to form chromatin.
• Plasmids are rare or absent.

Energy Metabolism:

• Energy is produced in mitochondria through cellular respiration.
• Photosynthetic eukaryotes (e.g., algae) use chloroplasts for photosynthesis.

Reproduction:

• Reproduce both sexually and asexually.
• Sexual reproduction involves meiosis and the formation of haploid gametes.
• Genetic exchange occurs during sexual reproduction.

Comparison of Prokaryotes and Eukaryotes