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1.3.1. Prokaryotic cell

Prokaryotic cells

Prokaryotic organisms were the first living things to appear on Earth, around 3.5 billion years ago. Its internal structure was very simple, with the DNA dispersed in the cytoplasm, in a region called the nucleoid that was not separated from the rest of the cytoplasm.

Prokaryotic cells are small, between 1 and 10 µm.

The structure of a prokaryotic cell is as follows:

  • Bacterial capsule. Some prokaryotic cells may have a thick, rigid capsule that surrounds them on the outside.
  • Cell wall. Rigid and strong envelope that shapes the cell located between the plasma membrane and the bacterial capsule (if any).
  • Plasma membrane. It is responsible for regulating the entry and exit of substances into the cell. In some places, the plasma membrane folds inward to form mesosomes, structures that are involved in cellular respiration and reproduction.

Remember that prokaryotic cells do not have membranous organelles and their activity is carried out in the membrane.

  • Cytoplasm. Interior space delimited by the plasma membrane.
  • DNAIt is made up of a circular DNA molecule. It is dispersed in the cytoplasm, in an area called the nucleoid.
  • RibosomesOrganelles that are in the cytoplasm responsible for protein synthesis. Ribosomes are the only organelles present in prokaryotic cells.
  • FlagellaThey 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 substrate or exchanging molecules with other cells or with the outside world.

Célula procaritoa

By Mariana Ruiz LadyofHats. Translated by JMPerez. (Original English version) [Public domain], via Wikimedia Commons

Prokaryotic cells can have different shapes:
  • Elongated or medicinal capsule shape: bacilli.
  • Spherical shape: coconuts.
  • Spiral shape: spirals.
  • Comma shape: vibrios.

Formas que pueden tener las bacterias

Por Mariana Ruiz LadyofHats [Public domain], undefined


         

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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.