Microbiology Quiz on Prokaryotic Cells

Prokaryotic Cells and Microorganisms

• Prokaryotic cells are a fundamental type of cell, lacking a membrane-bound nucleus and other organelles
• A wide variety of organisms fit this definition, including bacteria and archaea
• Key characteristics of life, including reproduction, growth, metabolism, movement, and transport, apply to prokaryotic cells and organisms.
• Reproduction involves producing offspring sexually or asexually.
• Growth involves an increase in size of individuals or populations.
• Metabolism encompasses the chemical and physical processes that cells need to function.
• Movement and irritability involve responding to internal and external factors.
• Transport involves moving nutrients in and waste out of the cell.

Traditional Definitions of Cell Types

• Eukaryotic cells include animals, plants, fungi, and protists.
• These cells contain membrane-bound organelles that perform specific functions.
• A double-membrane-bound nucleus houses DNA chromosomes.
• Prokaryotic cells include bacteria and archaea.
• Prokaryotes lack membrane-bound organelles and a nucleus.
• The term "prokaryote" may be problematic, as certain defining features are not shared by all bacteria and archaea.

Bacterial Cell Structures

• Cell envelope (cell wall): Provides structural support and shape. Composed of peptidoglycan.
  • Gram-positive cells have a thick layer, whereas gram-negative cells have a thin layer.
• Plasma membrane: Regulates the flow of materials and waste in and out of the cell.
• Glycocalyx: Outer coating (slime layer, capsule). Offers protection and attachment.
• Flagella: Involved in cell movement. Can be found at one end of the cell or many locations along the cell walls and membranes. Diverse arrangements.
• Fimbrae/Pili: Fine hairlike extensions that help with adhesion and in some cases, DNA transfer.
• Internal Structures: Include ribosomes, inclusion granules, the nucleoid (bacterial DNA), cytoskeleton, and (in some species), endospores.
• Ribosomes: Protein synthesis.

Cell Shape, Size, and Arrangement

• Coccus (coccus) - sphere

• Bacillus (rod)

• Coccobacillus (very short)

• Vibrio (gently curved)

• Spirillum (spirals)

• Spirochete (spring-like, flexible)

• Size varies from 0.3 μm (smallest) to several hundred μm (largest).

• Shape plays a role in functionality and adaptation

• Arrangement depends on division pattern and attachment after division. Common arrangements are singles, pairs (diplo), clusters, chains, and packets.

• Specific arrangements aid in species identification.

• Surface-to-volume ratio relates to nutrient uptake

• Small size may offer some protection from predation.

Bacterial Internal Structures, Granules, and Storage

• Intracellular storage bodies
• Vary in size, number, and content.
• Bacterial cells utilize internal storage bodies when environmental resources are low.

Bacterial Cytoskeleton

• Many bacteria have an internal network of protein polymers closely associated with the cell wall
• Plays a role in cell shape and division

Endospores

• Dehydrated, metabolically inactive structures that create high resistance.
• Highly resistant to a range of environmental factors
• Sporulation is the process of forming endospores.

Bacterial Ribosomes

• Responsible for protein synthesis, crucial to life process regulation
• Differ structurally from ribosomes in eukaryotic cells

Prokaryotic Taxonomy

• A system for organizing prokaryotes using systematic nomenclature criteria (identification, nomenclature, and classification).
• Based on evolutionary relationships, reflecting current knowledge about these organisms

Gram-staining and Identification

• Gram stain differentiates bacteria based on their cell wall structure
• Gram-positive bacteria retain the crystal violet stain, gram-negative bacteria lose it and take on a counterstain like safranin.
• This helps classify and identify bacteria, aiding diagnosis and clinical treatment.

Non-typical Cell Walls

• Some bacteria lack typical cell walls
• Mycobacterium and Nocardia have unique cell walls.
• Mycoplasma have no cell walls
• Acid-fast staining is used to identify bacteria with mycolic acid-containing walls.