What is meant by a typical cell

Prokaryote - Eukaryote: A comparison

If you look at the living beings who live with us on earth, there are a multitude of different possibilities Characteristics of life (growth, movement, metabolism, irritability, reproduction) to meet.

There are highly efficient unicellular organisms (e.g. Escherichia coli [E. coli], yeast or Euglena) in contrast to highly complex organisms, which, such as humans, consist of up to 1014 Cells exist! That is not to say that unicellular organisms are "simple". On the contrary: Microorganisms in particular colonize habitats that require very special adaptation and high metabolic complexity!

Animal (eukaryotic) cell. The complex cell contains a nucleus.

The same applies to the presence of a cell nucleus. In many organisms there is a special compartment for the storage of the genetic material, other living things do not have this subdivision. Both work fine, however.

Prokaryotic cell shown using E. coli as an example.
Click here to expand
  • Prokaryote (or prokaryote) = without a nucleus
  • Eukaryote (or eukaryote) = with a nucleus

 

Organisms

 

Classification

without Cell nucleus

With Cell nucleus

 

= Prokaryotes

= Eukaryotes

size

1-2 µm

up to 100 µm (example: human egg cell)

Cell membrane

Lipid bilayer with embedded proteins;

Archaea: special linkage of phospholipids (-> ethers instead of esters)

Lipid bilayer with embedded proteins

Cell wall

The cell membrane is often surrounded by a layer of polysaccharides of varying thickness

Only plant cells have a cell wall: cell wall deposited on cell membrane (mostly made of cellulose; brings stability)

Organelles

Vacuoles

endoplasmic reticulum (ER)

Golgi apparat

Cell nucleus

Lysosomes

Mitochondria

Vacuoles

Microbodies

Plastids, e.g. chloroplasts

Eukaryotes and prokaryotes show similarities and differences in structure.

Prokaryotes are usually single-celled and very small (approx. 1–2 µm). Eukaryotes are mostly multicellular organisms (there are exceptions such as yeast or the sun animal Heliozoa), the cells of which are significantly larger than those of the prokaryotes (10-100 µm).
While prokaryotes do not have a cell nucleus and are simply organized (only with regard to their architecture, but not with regard to their possibilities for metabolic reactions or colonization of various, often extreme habitats), eukaryotes with their cell organelles show an extremely complex intracellular organization.

Eukaryotes and prokaryotes - different organization of the genome

Eukaryotic genes:

  • can be found on long nucleic acid chains
  • these can condense to form chromosomes
  • are located in the cell nucleus
  • consist of coding information (exons) and non-coding information (introns)

Bacterial genes:

  • Hereditary information is available as a single, circular chromosome
  • extrachromosomal genes on plasmids are also possible
  • no division of the cell interior into organelles and compartments
  • Genes can partially overlap and are never interrupted by introns

Viral genes:

  • single or double stranded DNA or RNA molecules
  • associated with various nucleocapsid proteins
  • enclosed by capsid (= protein shell)
Click here to expand

Viruses are not living beings and always need a host to be able to "live"!

Similarities between prokaryotes and eukaryotes

One thing they have in common is the structure of the cell membrane: in both cases there is a lipid bilayer. Proteins are characteristic of this double layer. They traverse it and perform two important functions: transport and communication.

In addition, all cells have DNA as hereditary information, which is stored in the cytoplasm of the prokaryotes and in the nucleus of the eukaryotes. The processes of protein biosynthesis generally follow a certain pattern (DNA -> mRNA -> protein; genetic code ...), even if different proteins or ribosome types are used for this. So life as we know it today can only have come into being after this general process has been developed.