Prokaryotic Cell Structure
- The cell structure of organisms determines whether they are prokaryotic or eukaryotic
- Prokaryotes have the simplest cell structure, being the first organisms to evolve on Earth and have been classified into two domains:
- Bacteria or Eubacteria - 'true' bacteria, includes commonly known bacteria such as E.coli and Helicobacter
- Archaebacteria or Archaea - typically found in extreme environments such as high temperatures and salt concentrations and include methanogens (organisms that exist in anaerobic conditions and produce methane gas)
- Prokaryotic cells are small, ranging from 0.1µm to 5.0µm
- Prokaryotes have cells that lack a nucleus (the greek roots of prokaryote are 'pro' = before and 'karuon' = nut or kernel, relating to 'before the nucleus')
Cell structure
- The cytoplasm of prokaryotic cells is not divided into compartments, it lacks membrane-bound organelles (except for ribosomes)
- Prokaryotic ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S)
- The cell wall acts as protection, maintains the shape of the cell and prevents the cell from bursting
- Plasmids
- Capsules
- Flagellum
- Pili
- Plasmids contain genes that can be passed between prokaryotes (e.g. genes for antibiotic resistance)
- It helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism
- Some prokaryotes have more than one
- They assist with movement, avoidance of attack by white blood cells, conjugation (the sexual mode for bacteria) and are commonly used to allow bacteria to adhere to cell surfaces
Prokaryotic cells are often described as being ‘simpler’ than eukaryotic cells, and they are believed to have emerged as the first living organisms on Earth
Exam Tip
Make sure you learn the typical structures and organelles found in prokaryotic cells, as well as their functions.
