Functional Anatomy of Prokaryotic and Eukaryotic Cells: Comparative Structure and Organization

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Introduction

This chapter provides a comparative overview of the structural and functional features of prokaryotic and eukaryotic cells, which are the two fundamental cell types in microbiology. Understanding these differences is essential for studying microbial physiology, taxonomy, and the mechanisms of disease.

Two Kinds of Cells

Classification of Cell Types

Cells are broadly classified into prokaryotes and eukaryotes based on their structural organization and genetic material.

• Prokaryotes: Organisms whose cells lack a true nucleus and membrane-bound organelles. Includes Bacteria and Archaea.

• Eukaryotes: Organisms whose cells possess a true nucleus and various membrane-bound organelles. Includes Animals, Plants, Algae, Fungi, and Protozoa.

	Prokaryotes	Eukaryotes
Non-Microorganisms	None Known	Eukarya: Animals, Plants
Microorganisms	Archaea, Bacteria	Eukarya: Algae, Fungi, Protozoa

Structural Overview of Prokaryotic and Eukaryotic Cells

Cell Diagrams and Terminology

The term prokaryote is derived from Greek for "prenucleus," indicating the absence of a membrane-bound nucleus. Eukaryote comes from Greek for "true nucleus," reflecting the presence of a defined nuclear envelope.

• Prokaryotic Cell: Contains cytoplasm, ribosomes (70S), plasma membrane, cell wall, nucleoid (genetic material), and sometimes flagella or pili.

• Eukaryotic Cell: Contains nucleus, cytoplasm, ribosomes (80S), plasma membrane, cell wall (in some), and various organelles (mitochondria, Golgi complex, lysosomes, etc.).

Key Differences Between Prokaryotic and Eukaryotic Cells

Genetic Material and Organization

• Prokaryotes:

  • DNA not enclosed in a nuclear membrane

  • Single, circular chromosome

  • DNA not associated with histone proteins

  • No membrane-enclosed organelles

  • Complex cell wall (if present)

• Eukaryotes:

  • DNA enclosed in a nuclear membrane

  • Multiple, linear chromosomes

  • DNA associated with histones and non-histone proteins

  • Membrane-enclosed organelles present (e.g., Golgi complex, mitochondria, lysosomes)

  • Cell wall, if present, is structurally simpler

Additional info:

• Cell Division: Prokaryotes divide by binary fission, while eukaryotes divide by mitosis and meiosis.

• Size: Prokaryotic cells are generally smaller (0.2–2.0 μm) than eukaryotic cells (10–100 μm).

• Ribosomes: Prokaryotes have 70S ribosomes; eukaryotes have 80S ribosomes (except in mitochondria and chloroplasts, which have 70S).

• Cell Wall Composition: Prokaryotic cell walls contain peptidoglycan (in bacteria); eukaryotic cell walls (if present) are made of cellulose (plants, algae) or chitin (fungi).

Summary Table: Differences Between Prokaryotic and Eukaryotic Cells

Feature	Prokaryotes	Eukaryotes
Nucleus	Absent	Present
Chromosomes	Single, circular	Multiple, linear
Histones	Absent	Present
Organelles	Absent	Present
Cell Wall	Complex (peptidoglycan)	Simple (cellulose, chitin, or none)
Ribosomes	70S	80S (cytoplasm), 70S (mitochondria/chloroplasts)
Cell Division	Binary Fission	Mitosis/Meiosis

Example:

Bacteria are classic examples of prokaryotes, lacking a nucleus and membrane-bound organelles. Human cells are eukaryotic, containing a nucleus and various organelles.