Prokaryotic Cell Structure
புரோகாரியோடிக் செல் அமைப்பு
Prokaryotes are not 'primitive'—they are evolutionary masters of efficiency. While you struggle with complex organelle coordination, bacteria replicate in 20 minutes. Do not mistake simplicity for weakness; their lack of compartmentalization is their greatest survival advantage.
The idea
Prokaryotic cells lack a membrane-bound nucleus and distinct membrane-bound organelles. The genetic material is naked, not enveloped by a nuclear membrane, and exists as a single circular DNA molecule. They possess 70S ribosomes and a complex cell envelope consisting of glycocalyx, cell wall, and plasma membrane. Bacteria, blue-green algae, mycoplasma, and PPLO are the primary representatives.
Why it matters
These are evolutionarily primitive, allowing for rapid multiplication and survival in diverse environments due to their simple, efficient organization.
NEET lens
NEET focuses on the 'lack of' features. Expect questions comparing 70S vs 80S ribosomes and the composition of the cell envelope. Memorize that PPLO is the smallest cell and lacks a cell wall. Do not confuse the nucleoid with a true nucleus; it is a high-yield trap.
Clinical significance
Mycoplasma are the smallest living cells and lack a cell wall, making them naturally resistant to penicillin-type antibiotics. In humans, Mycoplasma pneumoniae causes atypical pneumonia. Understanding this structural absence is the difference between a successful prescription and a failed treatment.
Introduction
Prokaryotic cell structure lacks membrane-bound organelles. The cell has a cell wall, plasma membrane, cytoplasm with ribosomes, and a nucleoid region (DNA, not membrane-bound).
Core concept
Cell wall: in most bacteria, peptidoglycan (murein). Gram+ thick peptidoglycan. Gram- thin peptidoglycan + outer membrane. Plasma membrane. Cytoplasm with 70S ribosomes. Nucleoid (circular DNA, no histone). Plasmids (extra circular DNA). Flagella, pili, fimbriae (surface structures). No membrane-bound organelles.
Go deeper
Mesosome: infolding of plasma membrane — involved in DNA replication, cell wall synthesis, respiration (substitutes for mitochondria in prokaryotes).
From Class 10
Bacteria are prokaryotes — they lack a true nucleus. Their cell structure is simpler but still complex.