Célula Procariota: Definición, Estructura, Clasificación y Función ✅

Introduction to Prokaryotic Cells

Overview of Prokaryotic Cells

• Prokaryotic cells are characteristic of unicellular organisms and date back approximately 3.5 billion years.

• The term "prokaryote" means "before the nucleus," indicating their simpler structure compared to eukaryotes.

Structure of Bacteria

• Bacteria possess a capsule, which is a viscous layer made of polysaccharides that can be organized (capsule), disorganized (slime layer), or form a network (glycocalyx).

• The capsule aids in adhesion to surfaces and provides protection against antibacterial agents and desiccation.

Cell Wall Characteristics

• Bacterial cell walls are complex and semi-rigid, crucial for maintaining shape and providing osmotic protection during cell division.

• Gram-positive bacteria have thicker peptidoglycan layers (~50%) compared to gram-negative bacteria (5-10%), affecting their staining properties.

Differences Between Gram-positive and Gram-negative Bacteria

Virulence Factors

• Gram-positive bacteria contain teichoic acids as virulence factors, while gram-negative bacteria have lipopolysaccharides.

• Gram-negative bacteria also feature an outer membrane absent in gram-positive species, contributing to their structural differences.

Membrane Structure

• The bacterial plasma membrane is a lipid bilayer regulating substance entry/exit; it typically lacks cholesterol.

Genetic Material and Organelles in Prokaryotes

DNA Organization

• Bacterial DNA is not enclosed within a nucleus but exists in the cytoplasm as nucleoid material; plasmids may also be present for adaptability.

Ribosomes and Cytoplasm

• Ribosomes are the only organelles found in prokaryotes, smaller than those in eukaryotes, responsible for protein synthesis.

Additional Structures: Fimbriae, Pili, and Flagella

Adhesion Structures

• Fimbriae are thin appendages aiding bacterial adhesion to surfaces; critical for pathogenicity by allowing attachment to host tissues.

Pili Functions

• Pili facilitate conjugation (DNA transfer between bacteria), motility, and adherence through specialized types like type IV pili.

Locomotion Mechanism

Bacterial Morphology and Characteristics

Bacterial Flagella Types

• Bacteria can be classified based on their flagella arrangement:

• Atrichous: No flagella present.

• Lophotrichous: A tuft of flagella at one or both ends.

• Peritrichous: Flagella distributed over the entire surface.

Unique Cellular Structures in Bacteria

• Some bacteria possess carboxysomes, which are protein-bound vesicles containing ribulose bisphosphate carboxylase, crucial for carbon dioxide fixation, especially in autotrophic bacteria.

• Magnetosomes are another type of vesicle made of magnetite, allowing certain bacteria to orient themselves with Earth's magnetic field—a phenomenon known as magnetotaxis.

• Gas vesicles are found in aquatic bacteria like cyanobacteria, aiding in buoyancy.

Bacterial Cell Morphology

• Bacteria exhibit various shapes:

• Bacilli: Rod-shaped and elongated.

• Vibrio: Curved rod shape resembling a comma.

• Spirilla: Spiral-shaped with axial filaments.

• Cocci: Spherical or oval; can form different arrangements:

• Streptococci: Long chains of cocci.

• Sarcinae: Cubical or three-dimensional clusters.

• Staphylococci: Grape-like clusters.

Importance of Morphology

• The morphology of bacteria is essential for identification and differentiation. Understanding these forms aids in microbiological studies.

Archaea Characteristics

Adaptations of Archaea

• Archaea have evolved to thrive in extreme environments such as high temperatures and acidic conditions.

• They can survive below freezing temperatures and above 60 degrees Celsius, showcasing their resilience across diverse habitats.

Structural Variability

• Archaea display similarities to bacteria but also unique shapes like square forms, elongated structures, and flat configurations.

Functional Characteristics of Prokaryotic Cells

Nutritional Functions

• Prokaryotes play vital roles in nutrition through processes like carbon dioxide fixation via carboxysomes.

Metabolic Processes

• Despite lacking organelles, prokaryotes perform metabolism primarily at the cell membrane level.

Response to Stimuli

• Prokaryotes can respond to environmental stimuli, including orientation relative to Earth's magnetic field.