Lesson 3 of 13 · 6 min
Prokaryotic cells: general features
NCERT §8.4
The drop of curd under Riya's lens is swarming with rod-shaped cells far simpler than the ones scraped from her own cheek.
The lesson in notes
In short
Mycoplasma, PPLO (pleuro-pneumonia like organisms), bacteria and blue-green algae (cyanobacteria) all have prokaryotic cells.
They are generally smaller than eukaryotic cells and multiply faster. Bacteria come in four basic shapes: bacillus (rod), coccus (spherical), vibrio (comma) and spirillum (spiral).
Every prokaryote has a cell wall outside its cell membrane, with one exception: mycoplasma, which has no wall.
The genetic material is naked: not surrounded by a nuclear membrane. Besides the single genomic DNA (a chromosome, circular), many bacteria carry small circular extra-chromosomal DNA called plasmids.
Plasmids give bacteria special traits such as resistance to antibiotics; later in the course, plasmid DNA is used to monitor the transformation of bacteria with foreign DNA.
Apart from ribosomes, prokaryotes have none of the organelles found in eukaryotes. They do have inclusions, and a structure special to them is the mesosome, a specialised infolding of the cell membrane.