Functional Anatomy of Prokaryotic Cells

Functional Anatomy of Prokaryotic Cells

Introduction to Prokaryotes

Prokaryotes, which include the domains Bacteria and Archaea, are unicellular organisms characterized by the absence of a membrane-bound nucleus and organelles. They exhibit a wide variety of cellular forms and arrangements, which are important for their identification and classification.

• Prokaryotic cells are generally smaller and simpler than eukaryotic cells.

• They can be found in diverse environments and play essential roles in ecosystems, industry, and health.

Basic Shapes and Arrangements of Bacteria

Bacteria display several characteristic shapes and arrangements, which are useful for their identification:

• Coccus (spherical): e.g., Streptococcus (chains), Staphylococcus (clusters), Neisseria meningitidis (diplococci)

• Bacillus (rod-shaped): e.g., Bacillus anthracis

• Vibrio (comma-shaped): e.g., Vibrio cholerae

• Spirillum (spiral-shaped): e.g., Spirillum volutans

• Pleomorphic: variable shapes, e.g., Corynebacterium diphtheriae

Example: Streptococcus forms chains of cocci, while Staphylococcus forms grape-like clusters.

Comparison of Prokaryotic and Eukaryotic Cells

Key Differences

Prokaryotic and eukaryotic cells differ in several fundamental ways:

• Genetic Material: Prokaryotes have a single, circular chromosome located in a nucleoid region; eukaryotes have multiple, linear chromosomes within a membrane-bound nucleus.

• Organelles: Prokaryotes lack membrane-bound organelles; eukaryotes possess organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

• Cell Division: Prokaryotes divide by binary fission; eukaryotes divide by mitosis (and meiosis for sexual reproduction).

• Cell Wall: Most prokaryotes have a cell wall containing peptidoglycan (bacteria) or pseudopeptidoglycan (archaea); eukaryotic plant cells have cellulose cell walls, while animal cells lack cell walls.

• Cytoskeleton: Eukaryotes have an extensive, organized cytoskeleton; prokaryotes have a less developed cytoskeletal structure.

Example: The presence of mitochondria is a hallmark of eukaryotic cells, absent in prokaryotes.

Learning Objectives Overview

• Distinguish between prokaryotic and eukaryotic cells.

• Identify bacterial shapes and arrangements.

• Describe the structure and function of the glycocalyx.

• Differentiate external structures: flagella, axial filaments, fimbriae, and pili.

• Explain chemotaxis in motile bacteria.

• Compare and contrast cell walls of various prokaryotes and related groups.

• Describe the structure and function of the prokaryotic plasma membrane and transport mechanisms.

• Identify the functions of the nucleoid, ribosomes, and bacterial inclusions.

• Discuss endospores, sporulation, and germination.

• Summarize evidence for the endosymbiotic theory of eukaryotic evolution.

Visual Comparison: Eukaryotic vs. Prokaryotic Cell

The provided diagram highlights the structural differences between eukaryotic and prokaryotic cells:

• Eukaryotic Cell: Contains nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and other organelles.

• Prokaryotic Cell: Contains nucleoid (DNA), ribosomes, plasma membrane, cell wall, flagella, and sometimes plasmids.

Additional info: Eukaryotic cells are typically 10–100 μm in diameter, while prokaryotic cells are usually 0.1–5 μm.