Must we know:
1. The mode of Viral infection? Like some viruses attach to the cell membrane and inject their viral nucleic acid, and some are engulfed by the host cell itself. The viral nucleic acid then alters the normal DNA to reproduce more viral products and reassembles these into new viral particles. But should we know 'how' the viral DNA interrupts the normal DNA of the cell? Is it sufficient enough to just say that viral DNA alters normal functioning DNA of the host cell to produce more protein coats and viral DNA?
2. Why do some viruses in human cells get engulfed, but in bacterial cells just attach to the membrane? Is it because bacterial cells there is a rigid cell wall which may prevent/make it difficult for the virus particle to enter the cell, hence it just injects the viral nucleic acid in there? Whereas in humans, there is a lack of cell wall. If this is the case, what about plant cells? How do viruses infect plant cells, by directly entering the host cell or just injecting the viral nucleic acid in it?
3. "Because viruses enter host cells, it is difficult to inhibit the reproduction of a virus without interfeering with the metabolism of the host cell". This is true, however, would it not be effective in designing drugs to prevent the entry of viruses into host cells? For example, inhibiting the receptors which attach the virus with the membrane of the host cell?
4. I know bacterial cells have ribosomes and hence are responsible for the production of new protein components of new viruses, but where does the energy of bacterial cells come from? In other words, how do bacterial cells obtain their energy if they lack mitochondrion and chloroplast (in the case of photosynthetic bacterias)
5. Viroids are naked RNA molecules. So what? What makes them infectious pathogens to plants? Also is the key difference between a virus and viroid: viruses have protein coats and are composed of either DNA or RNA, whereas viroids lack a protein coat and are only RNA molecules?
Thank you .
1. As far as what you need to know, this is fine, except for the idea of "altering the normal DNA". This is not really what viruses do. Viruses can have different genomes. They could be ssDNA, dsDNA, ssRNA or dsRNA. How a virus produces new copies of itself completely depends on its genome. For those with ssRNA genomes, for instance, they can be directly transcribed by ribosomes (how they genome itself is replicated is another matter, but I won't go into that). The best way to approach it is to say this: viruses hijack the host cell machinery to replicate themselves. That is the VCE-level understanding required, which is a pain because it's so much more interesting than that!
2. That could be an explanation of it, but I suspect it's probably more complicated than that. Pretty sure viruses can enter plant cells. It could just be that bacteriophage have evolved a more efficient way of infecting cells that just hasn't evolved in eukaryotic viruses yet, although I think there are actually some eukaryotic viruses that insert their genomes this way...
3. The statement is actually not true. Inhibiting viral reproduction is tricky, but not impossible. Many viruses have to produce enzymes to get their genomes in a position to be replicated by the host machinery. Targetting these enzymes is a common theme in the rational design of anti-viral drugs. For instance, a drug called sofosbuvir has recently reached the market as a treatment for HepC virus. It targets a viral enzyme used in the replication of the viral genome. Most of the HIV antivirals target enzymes produced by HIV, namely reverse transcriptase, integrase and a protease.
You are completely right in saying, however, that targeting viral entry is a very good way of dealing with viruses. Some antivirals may actually prevent viruses from exiting the cell. Zanamivir is an influenza anti-viral that blocks an enzyme that allows viruses to exit cells.
4. Biology24123 is completely right on this. Most bacteria just take compounds from the environment and use those. It should be noted, however, that bacteria have really diverse metabolic strategies. Some will even use iron to produce energy. It should also be said that mitochondria and plastids are actually derived from bacteria. In the case of the former, alpha-purple bacteria were respiring before mitochondria, and in the latter cyanobacteria were photosynthesising before then. Lastly, I would also point out that bacteria can produce energy via glycolysis...
5. You've got the difference between the two right. The reason that viroids are infectious is because they can propagate disease between different organisms. The RNA jumps from cell to cell and gets replicated. IN the process, it causes disease.
It's a pity that they've called them viroids, because it makes it hard to remember. The reason they're called this, of course, is because they are essentially viruses without the virus.
In fact, a good way to think about it is to think of bacteriophage. What actually infects the cell? Only the RNA/DNA genome. The capsid just floats off.
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