Ch. 2

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Introduction

This chapter explores the structural and functional differences between prokaryotic and eukaryotic cells, which is fundamental to understanding microbiology. The organization, genetic material, and cellular components of these two cell types are compared to highlight their unique features and biological significance.

Comparing Prokaryotic and Eukaryotic Cells

Main Distinguishing Features

The primary feature that distinguishes prokaryotes from eukaryotes is the presence or absence of a membrane-bound nucleus and organelles.

• Prokaryotes lack a true nucleus; their genetic material is not enclosed within a membrane.

• Eukaryotes possess a nucleus surrounded by a nuclear membrane and contain various membrane-bound organelles.

Overview of Cellular Characteristics

Feature	Prokaryote	Eukaryote
Chromosomes	One circular chromosome, not in a membrane	Paired chromosomes, in nuclear membrane
Histones	No histones	Histones present
Organelles	No organelles	Organelles present
Cell Wall Composition	Bacteria: peptidoglycan; Archaea: pseudomurein	Polysaccharide cell walls (when present)
Cell Division	Binary fission	Mitosis

Size, Shape, and Arrangement of Bacterial Cells

General Characteristics

Bacteria exhibit a variety of sizes, shapes, and arrangements, which are important for identification and classification.

• Average size: Diameter ranges from 0.2 to 2.0 μm; length ranges from 2 to 8 μm.

• Monomorphic: Most bacteria maintain a single, consistent shape.

• Pleomorphic: Some bacteria can exhibit multiple shapes.

Common Bacterial Shapes

• Cocci: Spherical bacteria

• Bacilli: Rod-shaped bacteria

• Spiral: Includes vibrio (curved rods), spirillum (rigid spirals), and spirochete (flexible spirals)

Arrangements of Bacterial Cells

• Diplococci: Pairs of cocci

• Streptococci: Chains of cocci

• Tetrads: Groups of four cocci

• Sarcinae: Cube-like groups of eight cocci

• Staphylococci: Clusters of cocci

• Diplobacilli: Pairs of bacilli

• Streptobacilli: Chains of bacilli

Example

Streptococcus pyogenes is a bacterium that forms chains of cocci and is responsible for causing strep throat.

Additional info: The arrangement and shape of bacteria are used in clinical microbiology to help identify pathogens and understand their behavior.