Prokaryotic Cells

Overview of Prokaryotic Cells

  • Prokaryotic cells are typically smaller than eukaryotic cells, typically ranging from 1 to 5 micrometres in size.
  • Unlike eukaryotes, they lack membrane-bound structures called organelles.
  • A key characteristic of prokaryotes is that their DNA is not enclosed within a nucleus, instead, it is located in the nucleoid region of the cell.

Cell Wall and Plasma Membrane

  • The exterior of prokaryotic cells showcases a tough, protective cell wall which is made up of peptidoglycan in bacteria.
  • Inside the cell wall is the plasma membrane, a lipid bilayer that controls the movement of substances in and out of the cell.


  • The cytoplasm of prokaryotic cells is filled with a gel-like substance called cytosol, where cellular metabolism occurs.
  • Within the cytoplasm, there are various enzymes that catalyse biochemical reactions, and ribosomes that synthesise proteins.

Nucleoid and Plasmids

  • The nucleoid is an irregular region within the cell that contains the single DNA molecule of prokaryotes; it’s not surrounded by a nuclear membrane, differentiating it from a eukaryotic nucleus.
  • Alongside the main DNA, prokaryotic cells often contain smaller pieces of DNA known as plasmids; these are not essential for survival but may provide the cell with advantages such as antibiotic resistance.

Flagella, Pili, and Capsules (Where Applicable)

  • Some prokaryotic cells have a flagellum, a long whip-like structure that helps in motion.
  • Pili are small, hair-like structures on the surface of the cell that can aid in attaching to other surfaces and can be involved in DNA transfer.
  • Some prokaryotes are enclosed by a polysaccharide layer called a capsule, which provides extra protection, helps in attachment, and can evade the immune system of host organisms.

A well-rounded understanding of both prokaryotic and eukaryotic cells will help in comprehending the molecular interactions, functions and evolutionary relationships between different forms of life.