Viral diseases usually cannot be cured once they have been caught. Either the victim’s body fights off the
infection or it does not, although some antiviral drugs can help the host in the fight. However, viral
diseases can often be prevented by immunization, if a potential victim is vaccinated before catching the
virus. In this case, the invading virus will be killed by the immune system, which has been put on alert by
the vaccine, and the disease will be prevented.
Antibiotics are of no use against viruses; they only kill bacteria. So why do doctors often prescribe
antibiotics for viral diseases like flu or colds? There are two main reasons. The valid reason is that giving
antibiotics may help combat secondary or opportunistic infections caused by bacteria, especially in
virally-infected patients who are in poor health. However, massive over-prescription of antibiotics
occurs because many patients would be upset if faced with the truth. They would rather be given
medicine, even if it is of no use, than face the fact that there is no cure. This abuse has in turn
contributed to the spread of antibiotic resistance among many infectious bacteria thus creating a major
health problem.
immunization Process of preparing the immune system for future infection by treating the patient with
weak or killed versions of an infectious agent
DNA virus A virus whose genome consists of DNA
plasmid Self-replicating genetic elements that are sometimes found in both prokaryotic and eukaryotic
cells. They are not chromosomes nor part of the host cell’s permanent genome. Most plasmids are
circular molecules of double stranded DNA although rare linear plasmids and RNA plasmids are known
retrovirus Type of virus which has its genes as RNA in the virus particle but converts this to a DNA copy
inside the host cell by using reverse transcriptase RNA virus A virus whose genome consists of RNA
viroid Naked single-stranded circular RNA that forms a stable highly base-paired rod-like structure and
replicates inside infected plant cells. Viroid’s do not encode any proteins but possess self-cleaving
ribozyme activity
Prions are infectious protein molecules
transposable element or transposon Segment of DNA that can move as a unit from one location to
another, but which always remains part of another DNA molecule
DNA molecules in free solution will all move toward the positive electrode at the same speed,
irrespective of their molecular weights.
Electrophoresis of DNA is usually used to separate the DNA into different sizes.
The pore size of agarose is suitable for separating nucleic acid polymers consisting of several
hundred nucleotides or longer.
Shorter fragments of DNA as well as proteins are usually separated on gels made of
polyacrylamide.
Alternatively, the gel can be stained with ethidium bromide, which binds tightly and specifically
to DNA or RNA.
. Pulsed field gel electrophoresis (PFGE) is used for analysis of very large DNA molecules from 10
kb to 10 megabases.
