Q.What are the characteristics of prokaryotic cells?

Prokaryotic cells are the simpler of the two great cell types, found in bacteria, blue-green algae (cyanobacteria), mycoplasma and PPLO. Their chief characteristics are:

• They are generally smaller than eukaryotic cells and multiply more rapidly.
• They have no well-defined nucleus; the genetic material lies essentially naked, not wrapped in a nuclear membrane.
• The genomic DNA is a single circular chromosome; many bacteria also carry small extra circles of DNA called plasmids, which can give traits such as antibiotic resistance.
• Apart from ribosomes, they lack all the membrane-bound organelles found in eukaryotes.
• A cell wall usually surrounds the cell membrane (mycoplasma is the exception), enclosing a semi-fluid cytoplasm. …

All living things are made of cells, and these fall into two grand types of organisation. Prokaryotic cells represent the simpler design. They are the kind of cell found in bacteria, blue-green algae (the cyanobacteria), mycoplasma and PPLO (Pleuro Pneumonia Like Organisms). Compared with eukaryotic cells they are generally smaller and tend to multiply more quickly, and they vary greatly in both shape and size. Bacteria, for instance, come in four basic shapes — rod-like bacillus, spherical coccus, comma-shaped vibrio and spiral spirillum — yet the underlying organisation of every prokaryotic cell is fundamentally the same.

The defining features can be gathered under a few headings:

• Genetic material: There is no well-defined nucleus. The DNA is not enclosed in a nuclear membrane but lies essentially naked in the cytoplasm. The main genomic DNA is a single circular chromosome. In addition, many bacteria carry small circular DNA molecules, separate from the genome, called plasmids. Plasmid DNA can confer distinctive abilities on the cell, a well-known example being resistance to antibiotics.
• Organelles: Apart from ribosomes, prokaryotic cells contain none of the membrane-bound organelles that eukaryotes possess. The cell interior is filled with a semi-fluid cytoplasm.
• Boundary: A cell wall normally surrounds the cell membrane, the one exception being mycoplasma, which has no wall. Most bacterial cells are further wrapped in a chemically complex, three-layered cell envelope. …

Method: Group scattered facts under a small, fixed set of headings

"What are the characteristics of X" questions reward organisation over sheer volume — a long unsorted list of facts scores worse than the same facts grouped under a handful of clear headings, because grouping shows the examiner you understand which facts belong together. For prokaryotic cells, a reliable set of headings is: genetic material (how DNA is packaged, and any extra DNA elements), organelles (what's present vs. absent), boundary structures (what encloses the cell), and any named unique structure the syllabus calls out (mesosome, inclusion bodies). …