NOTES: 20.1 - Viruses (pages 574-579; 588-592)
What is a virus?
● viruses are
made up of
not both) and
that can invade living cells
(DNA or RNA…
Are Viruses Alive?
● like living things, viruses have genetic material and they can pass this on to future generations
● BUT, unlike living things, viruses
● outside of a cell, they
● Therefore, most biologists consider viruses
What do Viruses do?
● viruses can invade the cells of
● viruses cause illnesses like
,
,
,
, AIDS, polio, rabies,
measles, mumps…
How are viruses named?
● since viruses are non-living they are not named in the same way that living things are named
● many viruses are named for the disease that they cause or the organ/tissue they infect
● EX:
(infects adenoid tonsils)
What do Viruses look like?
● a virus is made of a core of genetic material surrounded by a protein coat (
● viruses are
)
!!(20-400 nanometers)
● viruses come in a variety shapes: rod-shaped; tadpole-shaped; helical; cubelike (see pg 575)
How does a virus get into a host cell?
● the proteins on the outer coat (capsid) of the virus attach to a
.
● Analogy:
● this attachment process is
!
 each virus can usually only attach to a few kinds of cells
How do Viruses Reproduce?
1) LYTIC CYCLE
● viruses insert their genetic material into a
● once inside, the
the cell’s machinery (ribosomes, etc.)
● The “hijacked” cell transcribes the viral genes
-uses the host cells own enzymes (e.g. DNA polymerase) & raw materials to make
.
● the cells
(burst) when the concentration of new viral particles is high
● the lytic cycle has its name because the host cell lyses and allows viral particles to escape
● the new viruses can then
2) LYSOGENIC CYCLE:
● begins like the lytic cycle (
);
● the viral DNA is integrated into the host cell’s chromosome – now called a
.
● the provirus may remain dormant, but every time the host cell reproduces, the provirus is also replicated and
passed along to the
.
● the lysogenic phase may continue for many years;
● at any time, the provirus may be
.
EX: cold sores caused by herpes simplex I virus (the provirus remains in your cells; when it enters a lytic cycle, a
cold sore forms)…WHY does this happen?
Examples of Lysogenic Viruses:
●
●
●
(may erupt later in life as shingles)
Retroviruses
● contain
as their genetic material
● retroviruses infect a cell and produce a DNA copy of their RNA
-(retro =
;
)
● this DNA is inserted into the host cell's DNA
● example of retrovirus:
Retrovirus example: HIV
● HIV =
● infects white blood cells (
)
● the viral genetic material becomes a provirus – infected person may not know it, but can still
● eventually, white blood cell count drops too low and
How Can You Protect Yourself From Viral Infections?
● The best way:
-Preparation of
or viral proteins
-When injected, the vaccine
-Sometimes produces permanent immunity
● Protect yourself
-Stay away from known sick people
-
(i.e.
/
sleeve; don’t share food or drink with sick people)
Viral Diseases:
●
●
●
●
●
(HIV)
●
●
(HPV) – linked to forms of cancer
into a tissue or your