Is a virus considered to be prokaryotic or eukaryotic?

Basics of microbiology and virology


The microorganisms include bacteria, fungi and viruses. As a carrier of a large number of sometimes life-threatening infectious diseases, knowledge of the structure, way of life, infection mechanisms and therapeutic approaches of these microorganisms is of particular relevance. Here is an overview of the basics of microbiological ecology, viruses and fungi. Bacteria are a very extensive topic and are dealt with separately under “Bacteria”.

Basics of microbiological ecology and infections

Ecology deals with the interaction between living beings and the environment and between living beings. Infectiology is an interdisciplinary discipline that deals with the course and effects of diseases caused by microorganisms (bacteria, fungi, parasites, viruses and prions).

Cell types

Energy cycle within an ecosystem

  • Ecosystem: community of all microorganisms and abiotic factors in a biotope
  • Energy cycle between the different elements of the ecosystem
    • Producers: Plants produce organic compounds using solar energy
    • Primary consumers: users of plants and their products ("herbivores", herbivores)
    • Secondary consumers: feed on primary consumers ("carnivores", carnivores)
    • Destructors: convert organic substances back into inorganic substances
      • Bacteria and fungi utilize waste products from all producers and consumers
      • Inorganic substances are again available to producers
  • Food chain
    • Hierarchy of the above-mentioned parts of the energy cycle (vegetable producer → herbivore → carnivore → destruent)
    • Introduced pollutants are passed on to the next links in the food chain

Mercury poisoning
By discharging industrial waste water, mercury can find its way into rivers and seas. It accumulates in the fish as methylmercury. Frequent consumption of fish poisoned with methylmercury can lead to chronic mercury poisoning in humans, which manifests itself, among other things, in damage to the central nervous system and the kidneys. In this case, the mercury did not reach humans directly, but via the food chain.

Interrelationships between different organisms

  • Symbiosis: coexistence of two species for mutual benefit
  • Commensalism: Use of a host organism with no benefit or harm to it
    • Examples:
      • Colonization of the skin with numerous germs that feed on exfoliation but are of no particular benefit to humans
      • Lions leave food scraps for vultures to eat
  • Parasitism: Use of a host organism with simultaneous damage to it
    • Example: The female Anopheles mosquito sucks the blood of its host, whereby the malaria is transmitted and can even lead to the death of the host

Infection and pathogenicity

The meeting of microorganisms and humans can proceed differently.

  • Colonization: colonization of the skin and mucous membranes with microorganisms without clinical symptoms or invasion of the body
    • This "natural flora" occurs in every person, but its composition is individual
      • It is true that some pathogenic agents can also be found here, but the microorganisms of the "natural flora" prevent them from growing and thus from infecting the organism
  • Invasion: Active penetration into tissues and cells
  • Infection: Penetration and multiplication of pathogens in a host organism, which typically causes a defense reaction and / or damage with signs of inflammation
  • Opportunistic infection
  • Nosocomial infection: infection that is temporally related to a hospital stay or an outpatient / inpatient medical measure (e.g. also care facilities, old people's home)
  • Zoonosis
  • Virulence: extent of pathogenicity

Course of infections

Depending on how widespread an infection is in the population, one speaks of an endemic, epidemic and / or pandemic. Infectious diseases show a heterogeneous but typical course.

  1. Contact with a pathogen in sufficient quantity (so-called infectious dose)
    • It is mostly absorbed through natural body orifices (e.g. via the airways or faecal-oral)
  2. Disease occurs after the incubation period has expired
  3. The disease can heal, persist or lead to death
  4. If the disease heals, lifelong immunity is possible with some pathogens (e.g. mumps or rubella)

Hand disinfection


Viruses consist of only one nucleic acid (DNA or RNA), have no metabolism, replication and protein biosynthesis equipment and are therefore dependent on host cells: They attack them, multiply with their equipment and are then released, destroying the host cell. They belong to the parasites.

Virus concept

  • Obligate parasites: completely dependent on a host cell for replication and protein biosynthesis
  • Possible host cells
    • Eukaryotic cells, e.g.
      • People
      • Animals
      • Plants: Infection by so-called "viroids"
        • Viroids: Small RNA molecules
    • Prokaryotic cells: Viruses that specifically infect bacteria are called "bacteriophages"
  • Virion: Extracellular (i.e. outside a host cell) virus particle that is mostly infectious

Viruses are parasites that need host cells to multiply!

Build up of viruses

  • Nucleic acid: Contains genetic information of the virus in various possible forms
    • Single stranded (ss) or double stranded (double stranded = ds)
    • DNA or RNA
  • Capsid: The protein envelope surrounding the viral nucleic acid
  • Nucleocapsid: nucleic acid and capsid of a virus
  • Virus envelope
  • Criteria for classifying viruses
    • DNA or RNA
    • Single-stranded (ss) or double-stranded (ds) genome
    • Uncovered or covered
    • Shape of the capsid: icosahedral or helical
    • Sensitivity to chemical or physical influences

A virus contains either DNA or RNA!

Viral life cycle

The replication cycle of bacteriophages and that of viruses of eukaryotic cells is different. Here only the reproduction cycle of the latter is discussed. Viruses get into their respective host organ after infection; There they go through a long replication cycle, at the end of which the individual components are stored together.

  1. Attachment (adsorption) to the host cell: Infection with viruses depends on surface features of the host cells (e.g. the HI virus infects all cells with CD4 surface features)
  2. Penetration into the host cell