Download Question: How can viruses mutate if they`re not considered alive? Is

Question: How can viruses mutate if they're not considered alive? Is it just that our
scientific definition of what's "alive" needs to change?
First review a few characteristics of life:
• All living things are composed of one or more cells
• Living things grow and reproduce
• They carry out metabolism (chemical transformations)
• They maintain a state of homeostasis
Where Do Viruses Fit?
• Not a cell
• Nucleic acids in protein shell
• Do not grow, do not maintain homeostasis, and do not metabolize on their own
• Use host cell to replicate
Question: How can viruses mutate if they're not considered alive? Is it just that our
scientific definition of what's "alive" needs to change?
Review Chapter 21 figures on the Lytic and Lysogenic life cycles.
Viruses mutate during the process of DNA or RNA replication.
Viruses that contain DNA genetic material tend to be stable through time because of the
proofreading process that DNA undergoes during replication.
Viruses that contain RNA genetic material are dynamic (that is mutate relatively quickly)
because RNA replication does not have the same proofreading mechanism in place.
Source: How viruses mutate
Question: I know that we can kill bacteria using anti-bacterial sanitizer and penicillin
and whatnot, but what's the life expectancy of one bacterial cell, and what exactly is it
that it "dies" of?
It depends. Bacteria experience cell death when they can no longer reinitiate cell division.
So environmental conditions that do not favor cell division, or otherwise disrupt the cell,
will cause cell death. However, some bacteria can survive in a dormant state indefinitely
as endospores.
Source
Question: Is there a lifespan of a virus? How would a virus die if it's not considered
alive? Could a virus continue to "live" if it's host died?
Using the definition of life given previously, viruses do not die per se but rather cease to
replicate. A virus can only continue to replicate as long as the host survives. Therefore,
the longer the host survives, the more opportunities the virus has to infect new hosts.
Question: Theoretically, could bacteria be used to kill/consume harmful bacteria and
possibly viruses? My understanding is that bacteria can push out an existing population
of bacteria (i.e., competitive exclusion), but can they kill each other?
Yes, bacteria do not play nice. They can excrete wastes that are harmful to other bacteria
strains as well as release restriction enzymes that can cut up the DNA of its competitors.
Source: Bacteria Fights to the Death
Question: Which one came first? The virus or the host?
Good question…
Genetic material that became independent of bacteria cells
Evolved completely independently of cellular life
Evidence that this happened very early on.
Source: Origins of viruses
Bacteria and humans as symbionts
We have 10-100 trillion bacteria in our guts.
These bacteria are critical to our ability to digest various foods.
Thousands of years ago, humans in Japan started to eat nori (a form of seaweed). In the
process they also ingested marine bacteria that can process nori carbohydrates.
Through horizontal gene transfer, gut bacteria received the genetic instructions to make
the same enzymes, thus facilitating the digestion of nori by humans.
Bacteria and humans benefit each other (mutualism)
Source: How the gut bacteria evolved to feast on sushi
Puzzling increase in autoimmune disorders, particularly allergies in the last two decades.
Working Hypotheses?
• Humans changed (gene pool)
• Environment changed (genetic modifications, additives, etc.)
• Increased awareness and reporting
• Under-stimulation of the immune system
• Overstimulation of the immune system
Hygiene hypothesis
Could our environment be too clean? (under-stimulation of immune system hypothesis).
Research in East and West Germany immediately after reunification indicated that
children raised in the dirtier environments were less likely to suffer from autoimmune
disorders.
Mechanism: appears to be the lack of challenge to the immune system at an early stage.
Immune system fails to distinguish nonpathogenic environmental stimuli from genuine
threats (pathogens).
More information about the Immune System and Allergies
Univ. of Virginia Health System
National Institute of Health Immune System Info Page
The Hygiene Hypothesis Clearinghouse