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Prokaryotic organisms were the first living beings to appear on Earth, some 3.5 billion years ago. Their internal structure was very simple, with DNA scattered in the cytoplasm, in a region called the nucleoid that was not separated from the rest of the cytoplasm.
- This is where DNA is found.
- One of the distinctive elements of a prokaryotic cell is that it lacks a nucleus. Instead it has a nucleoid, an irregular region located inside the cells.
DNA is made up of a circular DNA molecule. It’s dispersed in the cytoplasm, in an area called the nucleoid.
- Organelles in the cytoplasm, responsible for protein synthesis.
These are the only organelles present in prokaryotic cells.
- In some places, the plasma membrane folds inwards forming mesosomes, structures involved in cellular respiration and reproduction.
- Regulates the entry and exit of substances into the cell.
As well as this membrane, the structure of the prokaryotic cell contains:
Bacterial capsule: Some prokaryotic cells may have a thick, rigid capsule that wraps around the outside.
Cell wall: A strong, rigid envelope that shapes the cell between the plasma membrane and the bacterial capsule (if any).
Cytoplasm: Internal space delimited by the plasma membrane.
Flagella: They are extensions of the cytoplasm that allow movement in some bacteria.
Fimbriae and pili: They are short and numerous filaments that have various functions, such as fixing the bacteria to the substratum or exchanging molecules with other cells or with the outside.