Bacterial membranes — dominant phospholipids in eubacterial cytoplasmic membranes Which class of phospholipids is mainly present in the cytoplasmic (inner) membrane of typical eubacteria?

Introduction / Context:
Bacterial cytoplasmic membranes are lipid bilayers whose composition determines fluidity, protein function, and permeability. Recognizing the predominant lipid classes clarifies differences between bacteria, archaea, and eukaryotes and explains features like sensitivity to detergents and antimicrobial peptides.

Given Data / Assumptions:

• Eubacteria are “true bacteria,” distinct from Archaea.
• We focus on the inner membrane, not the outer membrane of Gram-negatives.
• Standard models emphasize glycerophospholipids as the main constituents.

Concept / Approach:
Eubacterial membranes primarily contain phosphoglycerides (glycerol backbone + phosphate + head group), notably phosphatidylethanolamine and phosphatidylglycerol, with cardiolipin in some species. In contrast, archaeal membranes feature ether-linked isoprenoid chains on glycerol-1-phosphate backbones; eukaryotes may include sphingomyelin and sterols. “Phospholipoprotein” is not a membrane-forming lipid class, and polyisoprenoids (for example, bactoprenol) serve as lipid carriers, not bulk bilayer constituents.

Step-by-Step Solution:
Identify the organism group: eubacteria.Recall predominant lipid class: phosphoglycerides.Eliminate distractors referring to carrier lipids or eukaryote-specific lipids.

Verification / Alternative check:
Biochemistry sources list PE, PG, and cardiolipin as common bacterial phosphoglycerides modulated by temperature and environment.

Why Other Options Are Wrong:

• B: Polyisoprenoids act as carriers (for example, undecaprenyl phosphate), not bulk bilayers.
• C: “Phospholipoprotein” is not a bilayer class.
• D: Incorrect because phosphoglycerides are present.
• E: Sphingomyelin is typical of animal cells, not bacteria.

Common Pitfalls:
Confusing archaeal ether lipids with bacterial ester-linked phosphoglycerides; they are chemically distinct.

Final Answer:
Phosphoglycerides (for example, phosphatidylethanolamine and phosphatidylglycerol)