Prokaryotic cell structure

first organisms to evolve on Earth
they still have the simplest structure
mostly small in size and found almost everywhere
they have a cell wall outside the cell membrane
- protects the cell
- maintains its shape
- prevents it from bursting
no nucleus is present in a prokaryotic cell
its interior is filled entirely with cytoplasm
there are no compartments
prokaryotes' size is 70 S (Svedberg units)
part of the cytoplasm appears lighter than the rest
- this region contains the DNA of the cell
  - usually one circular DNA molecule
  - the DNA is not associated with proteins
  - the lighter area of the cell = nucleoid
    - contains DNA but isn't nucleus

Cell division in prokaryotes

prokaryotes divide by binary fission
- used for asexual reproduction
steps:
- the single circular chromosome is replicated
- the two copies move to opposite ends of the cell
- the cytoplasm divides and the cell divides
- each daughter cell has a copy of the chromosome

1.2 - Ultrastructure of cells