Viruses: Living or
Non-living?
- a virus is a
microscopic particle capable of reproducing only within living cells
- viruses are biological particles and technically are not
considered to be living organisms
- when viruses are on their own, they are inert or non-living,
but once inside a cell, the virus shares one component with all living things
- reproduction.
- this makes viruses occupy a classification between living
and non-living matter.
The Nature of Viruses
- they are very small, smaller than cells; some are smaller
than many cell organelles.
- viruses are: colds, influenza, measles, polio, cold-sores,
rabies, and the mumps.
- approximately 5000 influenza viruses could sit on the head
of a pin.
Virus make up:
- inner nucleic acid core (or strand)
- surrounded by a capsid - a protein protective coating which
makes up 95% of the virus
- Bacteriophages - eaters of bacteria
- viruses contain either DNA or RNA (compared to cells)
- viruses are specific in function and infection (human colds)
2 Types of Viral Replication
- Lysogenic pathway - genetic material replicated with regular cell
replication
- Lytic pathway - new viruses are assembled and released
Aside: Phylogeny -
the history of the evolution of a species of a group of organisms.
Phylogeny of Viruses
- Since there is no fossil evidence to support the evolutionary
history of viruses, viral phylogeny is reduced to speculation.
- Many theories have been proposed and not one has been
proved.
- lived like parasites, gradually losing the need for
organelles of their own
- once free-living pre-cellular forms that became parasites of
cells
- arose from the detached fragments of genetic material of
cellular organisms.
Do questions 7-10 on page 425