Prokaryotic Cells Study Notes

Prokaryotic Cells Overview

Key Components of Prokaryotic Cells

• Plasma Membrane

  • Semipermeable membrane that regulates the import and export of nutrients.

• Cell Wall

  • Provides structure and protection from harsh environmental conditions.

• Capsule

  • A surface coating that may assist in pathogenicity.

• Pilus

  • Hair-like appendages involved in attachment to surfaces and in genetic transfer.

• Fimbriae

  • Short, hair-like structures that aid in adherence to surfaces.

• Cytoplasm

  • The gel-like substance inside the cell, where metabolic activity occurs.

• Ribosome

  • Organelle responsible for protein synthesis.

• Nucleoid

  • Region where chromosomal DNA is concentrated.

• Inclusion Bodies

  • Storage areas for nutrients and other substances.

• Plasmid

  • Small, circular, double-stranded DNA molecules that provide additional genetic advantages.

• Flagellum

  • Long appendage that aids in locomotion.

Learning Outcomes

• Identify Cell Parts:

  • Recognize various components found in bacterial cells, particularly those possessed by specific bacteria.

• Sporulation Process:

  • Describe the process through which bacteria can form spores for survival in challenging conditions.

• Glycocalyx Functions:

  • Explain the purpose of the glycocalyx, emphasizing its role in pathogenicity.

• Flagellar Types:

  • Name the four different flagellar types and their specific locations on bacterial cells.

Prokaryotic Cell Structure

• All Bacteria Possess:

  • Cell Membrane: For nutrient transport.

  • Chromosomal DNA: Genetic material located in the nucleoid region.

  • Ribosomes: For protein synthesis.

  • Cell Wall: Provides structural integrity; notable variations exist among bacteria.

• Some Bacteria Possess:

  • Cell Wall: Supports and protects cells.

  • Glycocalyx (Surface Coating): Involved in adhesion and protection.

  • Plasmids: Extra chromosomal DNA that can confer benefits like antibiotic resistance.

  • Endospores: Enable survival in extremes; found mainly in Bacillus and Clostridium species.

Cell Wall Composition

• Functionality:

  • Protects bacteria from environmental threats.

  • Made primarily of peptidoglycan, not found in other organisms, which resembles a fabric mesh.

• Gram-Negative vs. Gram-Positive Structures:

  • Gram-Positive Bacteria:

  • Thicker peptidoglycan layer (30-100 nm).

  • Contains teichoic acid, contributing to stability and pathogenesis.

  • Lacks outer membrane.

  • Gram-Negative Bacteria:

  • Thinner peptidoglycan layer (4 nm).

  • Contains two plasma membranes (inner and outer).

  • Contains LPS (lipopolysaccharides) which can function as an endotoxin contributing to septic shock.

Peptidoglycan Details

• NAG (N-Acetylglucosamine) and NAM (N-Acetylmuramic Acid) Components:

  • Gram-positive: Direct link of NAG and NAM.

  • Gram-negative: Thin layer with outer membranes contributing to structural properties.

Glycocalyx

• Definition:

  • A sugar coat surrounding the cell that enhances adhesion and biofilm formation.

• Types of Glycocalyx:

  • Capsule: Dense, thick layer that helps bacteria stick to surfaces and evade the immune response.

  • Slime Layer: Less organized, loosely attached layer providing moisture retention and nutrient protection.

• Biofilm Formation Examples:

  • Plaque on teeth protects bacteria from physical removal.

  • Colonization of medical devices (e.g., pacemakers, IUDs).

Bacterial DNA Characteristics

• Nucleoid:

  • The area within the cell where bacterial chromosomal DNA resides.

• Plasmids:

  • Small, circular, double-stranded DNA structures that can confer critical survival benefits such as antibiotic resistance.

Endospores

• Definition and Purpose:

  • Endospores are protective structures that allow bacteria to survive in unfavorable conditions, retaining genetic material in a dormant form.

• Conditions Prompting Endospore Formation:

  • Lack of nutrients or water, exposure to toxic chemicals, extreme temperatures, and radiation.

Vegetative Cells vs. Endospores

• Vegetative Cells:

  • Active, metabolically active cells sensitive to environmental extremes.

• Endospores:

  • Dormant cells that can withstand extreme conditions, having a dehydrated state and no metabolic activity.

Sporulation

• Process of Sporulation:

  • Transformation from a vegetative cell to an endospore, involving:

  1. DNA replication and septum formation to divide the cell.

  2. Formation of a cortex around the forespore containing DNA.

  3. A protective protein coat is formed as the mother cell disintegrates.

Germination

• Definition:

  • The reversal of endosporation; when an endospore becomes metabolically active and develops into a vegetative cell.

• Notable Pathogens:

  • Examples of endospore-forming bacteria include:

  • Bacillus anthracis (anthrax)

  • Clostridium tetani (tetanus)

  • Clostridium perfringens (gas gangrene)

  • Clostridium botulinum (botulism)

  • Clostridium difficile (pseudomembranous colitis)

Filamentous Appendages

• Fimbriae and Pili:

  • Fimbriae:

  • Short bristle-like structures important for attachment.

  • Pili:

  • Longer than fimbriae, they help with surface attachment and play a role in conjugation between bacterial cells.

Flagella Types and Functionality

• Flagella:

  • Responsible for bacterial motility.

  • Types of flagella:

  • Monotrichous: A single flagellum (e.g., Vibrio cholerae).

  • Amphitrichous: Flagella at both cell poles (e.g., Spirillum minor).

  • Lophotrichous: Tuft of flagella at one end (e.g., Pseudomonas aeruginosa).

  • Peritrichous: Flagella covering the entire surface (e.g., E. coli).

• Movement Mechanism: Runs and Tumbles:

  • Runs: Forward movement with flagella rotating counter-clockwise.

  • Tumbles: Involves clockwise rotation, occurring less frequently in the presence of attractants.

Motility Influenced by Gradients

• Chemical Responses:

  • Chemotaxis: Response to chemical gradients.

  • Phototaxis: Response to light gradients.

  • Magnetotaxis: Response to magnetic fields.