Microbial Cell Wall and Membrane: Structure, Function, and Diversity

Microbial Cell Wall and Membrane

Learning Outcomes

This section outlines the key objectives for understanding microbial cell walls and membranes, focusing on their structure, function, and diversity among different domains of life.

• Structure and Function of the Cytoplasmic Membrane: Describe the composition and roles of the cytoplasmic membrane in microbial cells.

• Bacterial vs. Archaeal Membranes: Compare and contrast the structural and functional differences between bacterial and archaeal membranes.

• Cell Wall Structure and Function: Explain the architecture and protective roles of the cell wall, including differences between Gram-positive and Gram-negative bacteria.

• Gram Staining: Understand the procedure and interpret results in relation to cell wall structure.

• Peptidoglycan Synthesis: Describe the chemical bonds and steps involved in peptidoglycan formation.

• Special Cell Envelopes: Recognize unique features of acid-fast bacteria and other envelope types.

• Borrelia burgdorferi: Discuss the cell wall structure, pathogenesis, and clinical aspects of this bacterium.

Cytoplasmic Membrane

Structure of the Cytoplasmic Membrane

The cytoplasmic membrane is a fundamental component of all microbial cells, serving as a selective barrier and interface for cellular processes.

• Phospholipid Bilayer: Composed of two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward.

• Proteins: Includes peripheral proteins (attached to the surface) and transmembrane proteins (spanning the membrane), which facilitate transport and signaling.

• Fluid Mosaic Model: The membrane is dynamic, with lipids and proteins able to move laterally within the layer.

Example: The bacterial cytoplasmic membrane contains proteins for nutrient uptake and energy generation.

Membrane Composition

The composition of microbial membranes varies between domains, affecting their stability and function.

• Bacterial Membranes: Typically contain phospholipids with fatty acid chains linked by ester bonds to glycerol.

• Key Components: Glycerol, fatty acids, phosphate groups, and additional molecules such as ethanolamine.

Example: The phospholipid bilayer provides a semi-permeable barrier for the cell.

Membranes of Archaea and Their Architecture

Archaeal Membrane Structure

Archaeal membranes are distinct from bacterial membranes, contributing to their ability to survive extreme environments.

• Ether Linkages: Archaeal lipids are connected to glycerol via ether bonds, which are more chemically stable than ester bonds.

• Isoprenoid Chains: Instead of fatty acids, archaeal membranes contain isoprenoid chains (e.g., phytanyl).

• Lipid Monolayers: Some archaea have lipid monolayers formed by diglycerol tetraethers, increasing membrane rigidity.

Example: Crenarchaeol is a unique archaeal lipid found in some extremophiles.

Feature	Bacteria	Archaea
Linkage	Ester	Ether
Lipid Tail	Fatty acids	Isoprenoids
Bilayer/Monolayer	Bilayer	Bilayer or monolayer

Additional info: Archaeal membranes are more resistant to heat and chemical stress due to their unique lipid composition.