Functional Anatomy of Prokaryotic and Eukaryotic Cells

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Introduction

This section introduces the fundamental differences between prokaryotic and eukaryotic cells, focusing on their structure, genetic material, and cellular organization. Understanding these differences is essential for studying microbial physiology and classification in microbiology.

Comparing Prokaryotic and Eukaryotic Cells

Definitions and Etymology

• Prokaryote: The term comes from Greek, meaning "before nucleus." Prokaryotic cells lack a true nucleus.

• Eukaryote: Derived from Greek, meaning "true nucleus." Eukaryotic cells possess a membrane-bound nucleus.

Key Differences Between Prokaryotic and Eukaryotic Cells

Feature	Prokaryote	Eukaryote
Genetic Material	Usually one circular chromosome, not in a nuclear membrane	Paired chromosomes, in nuclear membrane
Histones	Absent	Present
Organelles	Absent (no membrane-enclosed organelles)	Present (membrane-bound organelles)
Cell Wall	Bacteria: peptidoglycan; Archaea: pseudomurein	Polysaccharide cell wall (when present)
Cell Division	Binary fission	Mitosis

Additional info: Prokaryotes include Bacteria and Archaea, while Eukaryotes include animals, plants, fungi, and protists.

Size, Shape, and Arrangement of Bacterial Cells

General Characteristics

• Size: Most bacteria range from 0.2 to 2.0 μm in diameter and 2 to 8 μm in length.

• Shape: Most bacteria are monomorphic (single shape), but some are pleomorphic (variable shapes).

Common Bacterial Shapes

• Bacillus: Rod-shaped

• Coccus: Spherical-shaped

• Spiral: Includes three main types:

  • Vibrio: Curved rod

  • Spirillum: Rigid spiral

  • Spirochete: Flexible spiral

• Other shapes: Star-shaped, rectangular

Example: Vibrio cholerae is a vibrio-shaped bacterium; Treponema pallidum is a spirochete.

Arrangements of Bacterial Cells

• Pairs: Diplococci (pairs of cocci), Diplobacilli (pairs of bacilli)

• Clusters: Staphylococci (grape-like clusters of cocci)

• Chains: Streptococci (chains of cocci), Streptobacilli (chains of bacilli)

• Groups of four: Tetrads

• Cubelike groups of eight: Sarcinae

Additional info: The arrangement of bacterial cells is determined by the pattern of cell division and whether the cells remain attached after division.

Spiral Bacteria: Visual Examples

• Vibrio: Comma-shaped, slightly curved rod

• Spirillum: Rigid, wavy-shaped

• Spirochete: Flexible, corkscrew-shaped

Example: The provided images (not shown here) illustrate the differences in morphology among vibrio, spirillum, and spirochete bacteria.