Cell Structure and Function: Prokaryotic vs. Eukaryotic Cells

Chapter 3: The Cell

Part B: Cell Structure and Function

This section introduces the fundamental differences between prokaryotic and eukaryotic cells, focusing on their structure, function, and evolutionary significance. Understanding these differences is essential for microbiology, as it underpins the classification and physiology of microorganisms.

Comparing Prokaryotic and Eukaryotic Cells: An Overview

Definitions and Origins

• Prokaryote: Derived from Greek words meaning "prenucleus." Prokaryotic cells lack a true nucleus and membrane-bound organelles.

• Eukaryote: Derived from Greek words meaning "true nucleus." Eukaryotic cells possess a nucleus enclosed by a membrane and various membrane-bound organelles.

Classification

• Prokaryotes include Bacteria and Archaea.

• Eukaryotes include Protista, Fungi, Plantae, and Animalia.

Key Structural Differences

• Nucleus: Prokaryotes lack a membrane-bound nucleus; eukaryotes have a true nucleus.

• Chromosomes: Prokaryotes have a single, circular chromosome; eukaryotes have multiple, linear chromosomes.

• Organelles: Prokaryotes do not have membrane-bound organelles; eukaryotes possess organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

• Cell Size: Prokaryotic cells are generally smaller (0.2–2.0 μm in diameter); eukaryotic cells are larger (10–100 μm in diameter).

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

Examples and Applications

• Prokaryotes: Escherichia coli (bacterium), Halobacterium (archaeon).

• Eukaryotes: Saccharomyces cerevisiae (yeast), Amoeba proteus (protist), plant and animal cells.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No true nucleus	True nucleus present
Chromosomes	Single, circular	Multiple, linear
Organelles	Absent	Present (mitochondria, ER, etc.)
Cell Size	0.2–2.0 μm	10–100 μm
Cell Division	Binary fission	Mitosis/meiosis
Cell Wall Composition	Peptidoglycan (bacteria), pseudomurein (archaea)	Cellulose (plants), chitin (fungi), absent in animals

Additional info:

• Prokaryotic cells are evolutionarily older and are thought to have given rise to eukaryotic cells through endosymbiotic events.

• Both cell types contain ribosomes, but prokaryotic ribosomes are smaller (70S) compared to eukaryotic ribosomes (80S).