Prokaryotic vs Eukaryotic Cells: Key Differences and Structures

Prokaryotic Cells: Key Characteristics

• Nucleus: Absent.
• Plasma Membrane: Possesses a lipoprotein envelope similar to that of eukaryotes.
• Mesosomes: Infoldings of the plasma membrane containing numerous enzymes.
• Cell Wall: Present, but distinct from plant cells as it lacks cellulose; composed of nitrogenous substances.
• Capsule: In some cases, the wall is covered by a capsule composed of polysaccharides and proteins.

Cytoplasm and Genetic Material

The cytoplasm contains numerous 70S ribosomes and inclusions of reserve substances. The genetic material consists of a single-stranded, circular DNA molecule, weakly associated with proteins and localized in the nucleoid.

Plasmids and Appendages

Bacterial chromosomes often contain small rings of DNA called plasmids:

• F-plasmids: Provide conjugation capacity.
• R-plasmids: Contain information on enzymes that provide antibiotic resistance.

Bacterial appendages include flagella (composed of flagellin), fimbriae (long and numerous), and pili (longer, less numerous, involved in conjugation).

Eukaryotic Cells: Features

Eukaryotic cells feature a plasma membrane with specific proteins known as membrane receptors. The cytoplasm contains three main types of structures:

• Endomembrane System: Interconnected membrane structures and derived vesicles.
• Energy Transducing Organelles: Mitochondria and chloroplasts, both with double membranes, responsible for energy production via oxidation or sunlight.
• Non-membrane Structures: Ribosomes, centrioles, microtubules, and microfilaments.

The Nucleus

The nucleus is surrounded by a double membrane crossed by pores. Inside, it contains the nucleoplasm, condensed chromatin, and nucleoli.

Differences Between Plant and Animal Cells

• Cell Wall: Plant cells have a rigid cellulose cell wall; animal cells lack one.
• Vacuoles and Plastids: Plant cells have well-developed vacuoles and plastids for synthesis and storage. Animal cells have poorly developed vacuoles and lack plastids.
• Centrioles: Animal cells contain centrioles involved in cilia and flagella organization; plant cells lack them.