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#2 Prokaryotic Diversity
#3 Eukaryotic Origins
A.
Warm-Up
Talk about the issues with a partner.
1)
How small and big can life forms be?
2)
What are the smallest living things?
3)
How small are they?
4)
What is a virus?
5)
Is there a difference between a virus and a bacterium?
5.2 Reading Resource #1
: Viruses
Most
viruses
are much smaller and simpler in structure than eukaryotic or even prokaryotic
cells. Are viruses
alive
or
nonliving
? Viruses were once thought to be biological chemicals; the Latin
root for virus means “
poison
”. Viruses can cause a wide range of diseases, so researchers in the late
1800s saw a parallel with bacteria and proposed that viruses were the simplest of living forms.
Viruses, on the other hand, cannot reproduce or perform metabolic functions outside of a host cell.
The basic structure of all viruses is the same: a nucleic acid core surrounded by protein. This structure
does not have cytoplasm and is not a cell. Viruses only have one type of nucleic acid, either DNA or
RNA. The genome of DNA or RNA can be linear or circular, single or double stranded. RNA viruses
can be segmented (have multiple RNA molecules within a virion) or nonsegmented (have only one
RNA molecule).
Figure 74.
Structure of Coronavirus
Viruses are divided into three types based on the structure of their genomes:
RNA viruses
,
DNA viruses
, and
retroviruses
. Almost all
viruses form a protein sheath, or capsid, around their
nucleic acid core. The
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