Structure of Bacterial Cell — Core Principles

Core Principles

Bacterial cells are prokaryotic, meaning they lack a membrane-bound nucleus and other membrane-bound organelles. Their fundamental structure includes a rigid cell wall, primarily composed of peptidoglycan, which provides shape and protection.

Inside the cell wall is the plasma membrane, a selectively permeable barrier involved in transport and metabolic activities like respiration. The cell's interior, the cytoplasm, is a jelly-like substance containing ribosomes (70S type) for protein synthesis and a nucleoid region where the single, circular bacterial chromosome resides.

Many bacteria also possess plasmids, small circular DNA molecules carrying non-essential but often advantageous genes like antibiotic resistance. External to the cell wall, some bacteria have a glycocalyx (capsule or slime layer) for protection and adhesion.

Motility is often provided by flagella, long protein filaments, while pili (fimbriae) facilitate adhesion and genetic exchange. Some bacteria can form highly resistant endospores for survival in harsh conditions.

This unique organization allows bacteria to thrive in diverse environments and underpins their biological roles and interactions.

Important Differences

vs Eukaryotic Cell

Aspect	This Topic	Eukaryotic Cell
Nucleus	Absent (genetic material in nucleoid region)	Present (membrane-bound, contains genetic material)
Membrane-bound Organelles	Absent (e.g., mitochondria, ER, Golgi)	Present (e.g., mitochondria, ER, Golgi, lysosomes, chloroplasts)
Ribosomes	70S type (50S + 30S subunits)	80S type (60S + 40S subunits); 70S in mitochondria/chloroplasts
Cell Wall	Present in most, primarily peptidoglycan	Present in plants (cellulose) and fungi (chitin), absent in animals
Genetic Material	Single, circular chromosome in nucleoid; plasmids often present	Multiple, linear chromosomes in nucleus; no plasmids normally
Size	Typically 0.5-5 $\mu$m	Typically 10-100 $\mu$m
Cell Division	Binary fission	Mitosis and Meiosis
Sterols in Plasma Membrane	Generally absent (except Mycoplasma)	Generally present

Bacterial cells, being prokaryotic, fundamentally differ from eukaryotic cells in their internal organization. The most striking distinction is the absence of a true nucleus and other membrane-bound organelles in bacteria, with their genetic material residing in a nucleoid region. Bacterial ribosomes are smaller (70S) compared to eukaryotic ones (80S). While both can have cell walls, their composition is distinct (peptidoglycan in bacteria vs. cellulose/chitin in plants/fungi). These differences impact cellular complexity, metabolic pathways, and susceptibility to various antimicrobial agents, making this comparison a cornerstone of cell biology.