Viruses, per definition, are not alive as they don't have a metabolism. How then do they attach to a cell, make a hole into the cell membrane, inject their DNA into this cell, make it travel through the cell to the nucleus, enter the nucleus and splice it into the host DNA? These steps, or at least the first two of it, apparently require energy that has to come from the virus. Where does this energy come from, without any metabolism?
Viruses have evolved to attach to cells via receptors already existing on the cell surface. Therefore, the energy required for entry of the virus particle and the subsequent trafficking to the nucleus (depending on the virus) is provided entirely by the cell. For this, perhaps it's best to view the virus as the Trojan Horse of the Greeks - the wooden horse sat there passively, and was wheeled in actively by the citizens of Troy.
Similarly, for viruses whose genomes integrate into the host genome, the virus has evolved to harness pre-existing cellular pathways. It may contribute some proteins in order to do so, but does not need to provide any energy.
Thank you for this explanation. So the virus does not inject anything. Instead, the cell "sucks" the DNA/RNA out of the virus and uses existing mechanisms to integrate it into its own DNA? Have I got that right?
Yes, via endocytosis. I can recommend a very nice article (in German language) by Sieben et al., humboldt-spektrum 1-2/2010:
https://www.hu-berlin.de/de/forschung/szf/forschungsmanagement/veroeffentlichungen/spektrum/herrmann_1210.pdf
The subsequent access to the nucleus is elucidated in Cohen et al.,
Biochimica et biophysica acta 2011.
You are welcome. But what about bacteriophages? Instead of using endocytosis they dock to the bacterial cell and seem to actively inject their DNA into the host cell. Wikipedia states: “Once attached completely, irreversible binding is initiated and the tail contracts, possibly with the help of ATP, present in the tail,[4] injecting genetic material through the bacterial membrane. The injection is accomplished through a sort of bending motion in the shaft by going to the side, contracting closer to the cell and pushing back up.”
https://en.wikipedia.org/wiki/Bacteriophage#Attachment_and_penetration
So we are back to my orginal question then. Where do they get there ATP from? Is it a form of boxed lunch they take with them on their travel to the next host? Can ATP be stored?
Might this be the answer? - Elastic and electrostatic energy of the coiled up DNA?
"Several physical mechanisms by which bacteriophages inject DNA into their hosts have been identified. The specific mechanism varies by phage type and stage of the infection process [2–4]. A fast ejection on the timescale of seconds can be achieved simply by the release of elastic and electrostatic energy of the coiled up DNA confined within the viral capsid."
Article Capstan Friction Model for DNA Ejection from Bacteriophages
- Badges
- Science topic
- Similar topics
- Biological Science
- Microbiology
- Virology
- Virus