Cue Column | Notes Column

Definition | Cells lacking a membrane-bound nucleus. Kingdom Monera. Examples: Bacteria, Cyanobacteria (blue-green algae).

Size | 1–10 µm (smaller than eukaryotes, 10–100 µm).

Genetic Material | Single circular, double-stranded, naked DNA in nucleoid region. No histones. No linear chromosomes.

Plasmids | Small (1–200 kb), circular, extrachromosomal DNA. Replicate autonomously. Carry accessory genes (antibiotic resistance, toxin production). Used extensively in biotechnology.

Cell Envelope | Three layers (from outside in): (1) Capsule (polysaccharide — virulence factor, antiphagocytic); (2) Cell wall (peptidoglycan — murein; Gram+ thick, Gram− thin with outer membrane); (3) Plasma membrane (phospholipid bilayer).

Mesosomes | Infoldings of plasma membrane. Functions: increase surface area for respiration, DNA replication attachment site, cell wall synthesis during division. Only in prokaryotes.

Ribosomes | 70S = 50S (large) + 30S (small). Site of protein synthesis. Targets for antibiotics: erythromycin/chloramphenicol → 50S; streptomycin/tetracycline → 30S.

Flagella | Made of flagellin protein. Helical filament extending from basal body. Rotation powered by $H^{+}$ gradient (proton motive force). NO 9+2 arrangement. NO membrane covering.

Pili / Fimbriae | Short, hair-like projections. Functions: attachment to surfaces (adhesion), sex pili for conjugation (DNA transfer). Virulence factors (pathogenic bacteria).

Division | Binary fission: circular chromosome replicates → chromosomes segregate → septum forms → two daughter cells. No mitosis, no spindle, no centrioles. Fast (~20 min for E. coli).

Key NEET Points | (1) 70S ribosomes in ALL prokaryotes. (2) Peptidoglycan only in bacteria (murein). (3) Mesosomes only in prokaryotes. (4) Plasmids present (extrachromosomal). (5) No membrane-bound organelles of any kind.

Summary

Prokaryotic cells (bacteria, cyanobacteria) are 1–10 µm, lack a nuclear membrane, have 70S ribosomes (50S + 30S), peptidoglycan cell wall, mesosomes, and plasmids. They divide by binary fission without a spindle. Flagella are made of flagellin (no 9+2). Key NEET trap: ribosomes in organelles (mitochondria, chloroplasts) are also 70S.