Download 22 Virus Bacteria AP Bio 2015

22
Virus and Bacteria
AP Biology
Pages 392-407
Name: _______________________ Date: ____________ Period: _______
Scientists cannot agree on whether virus particles are living or not. Virus
particles are often 1/100 the size of bacteria and bacteria are often 1/100 the size of
mammalian cells (though this relationship can vary by a factor of ten). Virus particles
come in many different forms and sizes.
Tobacco Mosaic Virus
Human Immunodeficiency
Ebola Virus
Virus (HIV)
Viruses are usually specific. That means they will attach and/or invade specific types of
cells. For example, the tobacco mosaic virus will only attack tobacco plant cells. That
virus will not attack other plants such as a rose or an oak tree. HIV will only attach to
cells that exhibit a
CD4+ protein (a
surface receptor) on
the outside of the cell.
For the most part that
limits the cells to
human t-helper cells
(although two
monkey species have
similar enough
proteins on the
outside of their cells
to be infected by the
virus).
The life cycle of a
virus attacking a
bacterium is shown to
the right: (viruses that
invade bacteria are
called “Bacterial
phages” (or “phages”
for short).
Page 2 (Cont. #22 A/P Bio.)
Not all virus particles integrate their genetic material into the host cell DNA. If
the virus DOES integrate its genetic material into the host DNA it is called the lysogenic
phase. The virus DNA MAY remain dormant for some period of time before the viral
DNA becomes active and starts to take over the host cell machinery and make new virus.
If viral production occurs, it is referred to as the lytic phase- where virus particles are
released, causing irreparable harm to the host cell (bursting the cell membrane) or
“blebbing” out of the cell membrane causing small holes in the membrane which might
be repaired by the cell. The only way viruses can replicate is to invade a specific host cell
and somehow take over the machinery. To take over the host machinery, the virus has to:
1.) Attack - attach itself to the outside of a host cell (there MUST be a receptor)
2.) inject is genetic material into the host cell
3.) either begin to direct the cell’s machinery to make more viral particles
OR make a DNA copy that is integrated into the host’s DNA – meaning
the virus is lysogenic- which may become dormant or in turn will make
mRNA and new virus particles)
4.) Make provirus (that will eventually make vegetative virus)
5.) Vegetative virus develops into new mature virus particles
6.) Then the mature virus escape the host cell by breaking it apart completely (this
being the definition of a lytic virus- i.e. the host cell bursting to release many
virus particles - killing it) or leaving holes in the cell membranes that may or may
not be repaired (if repair is impossible, cell dies- if repair is possible the cell lives
and continues to make more virus particles).
Sometimes, when virus DNA is inserted into the host cell genome, the insertion
point disrupts a specific set of gene controlling the cell cycle. Certain genes controlling
the cell cycle are called oncogenes. When these genes are disrupted or interfered with,
the cell “may” become cancerous. HIV has been known to cause disruption in oncogenes
and may trigger cancerous tumors.
ONCE a host cell is invaded by a virus particle, it usually cannot perform its
normal function. What this means is if a Human T-Helper cell is invaded by
HIV, the T-Helper cell will not be able to assist the immune system in fighting off
diseases or infections!
---So there are two “stages” of viral particles:
1.) Lysogenic-Those that integrate their DNA into the host cell.
2.) Lytic-When viral particles “burst” out of a cell all at once – killing or injuring the cell.
A successful virus is one that does not kill a host animal before the virus can
reproduce and spread to other host organisms. This is basic Darwinian theory shaped
into a practical example. Virus particles can multiply at an incredible rate. The mere fact
that the virus replicates rapidly asks one to consider the evolution of such an organism.
We know that the faster an organism reproduces, the faster it MAY evolve. Though there
is not a lot of information about the evolution of virus (because there are no fossil records
or DNA records of early virus-at least none that we have the technology to detect), we
cannot be sure if all viruses evolve “rapidly”. However, we know that certain viruses
(such as HIV) mutate rapidly. Not necessarily because of environmental pressure, rather
Page 3 (Cont. #22 A/P Bio.)
because the virus itself is “flawed”. Now in this case, flawed does not mean the virus
will die off rapidly. In this case the virus does not make a true copy of its genetic
material. If we look at this pragmatically, we see that this is a viable strategy for the
virus particle. If the mutation made is a successful one, one that will allow the virus
particle to survive in a particular environment, then that successful mutation will be
selected to reproduce. If the mutation causes a lethal change in the DNA where it cannot
survive in a particular environment, then the mutation in the DNA is lost, and that
mutation failed. If the virus does this millions of times, it is likely to come up with one
or two strains that are very successful- and those are the ones that count and will survive!
Some examples of mutated virus are of course HIV and smallpox. However we
must not discount the fact that man can artificially mutate these viruses into more
virulent and deadly strains. These pathogens (organisms that can cause disease) CAN
be carried (by carriers, i.e. organisms that move virus particles, bacteria, or Protist
pathogens) from one organism to another. Those organisms that can support another
organism and/or pass it along are called hosts or carriers. Organisms that live off other
organisms, give nothing back, and often harm the host are called parasites. (Viruses can
be thought of as parasites if you decide they are “alive”.)
It is thought that virus particles could have been the original vector to transfer
genetic material from one organism to another. You can think of a vector as a carrier.
But in terms of evolution, we can speculate that bacteria, Archaebacteria, Eubacteria,
may have been the recipient of genetic material (perhaps from virus particles infecting
them) that allowed them to evolve into more complex organisms- purely by chance!!!
This leads us to believe that there was a sort of partnership going on between early
bacteria and viruses. There are even some articles that suggest that virus were the result
of bacteria “de-evolving” into simpler organisms. How is this possible when evolution
usually favors the production of complex organisms? Remember- the ENVIRONMENT
selects and puts pressure on organisms to change. What if the environment is a singlecelled organism or a multi-cellular animal that has little internal changes and that an
organism (a parasite) lives within a particular organism. (We have speculated on this
before…remember? Mitochondria invading a prokaryotic cell or chloroplasts invading a
prokaryotic cell.) So- there would be little to no pressure for the parasite (the “to be”
virus particle) to change, in fact it may de-evolve- become simpler to save energy and be
more successful within the environment of another organisms! This MIGHT be how virus
particles evolved…by the simplification of a bacteria that invaded a multi-cellular
organism (compared to mitochondria that invaded another organism (single cell)- only
the mitochondria did not become a parasite- it became an endosymbiotic organism!). The
de-evolution of the bacteria to a virus would have necessarily caused the circular DNA to
be broken into one or more strands. Certain articles have suggested that virus particles
MIGHT have become symbiotic with bacterial particles, absorbing the bacterial genetic
material (or destroyed it?) and took over the running of the entire cell. Thus the concept
that eukaryotic cells have strands of DNA rather than circular DNA. Consider that
scenario might lead to the formation of a nucleus! Think about it, the nucleus by
definition controls the cell…the basic premise of a virus is to take over the cell. The
difference lies in the lytic phase. If there is no lytic phase and the virus particle fails to
Page 4 (Cont. Handout #22 AP Biology)
make more virus, the virus may have the only source of instruction (DNA) in the cell (the
nucleus), then the virus has achieved the same TYPE of symbiotic relationship that the
mitochondria and chloroplast seem to have. What is the difference? The difference lies
in the STRUCTURE of the DNA! The viral DNA is stranded rather than circular-and the
viral strands are often found in pairs! For instance, HIV contains two copies of RNA in
the capsule of the virus. Eukaryotic DNA is stranded- NOT circular-and again found in
pairs!
So- if the bacteria picked up genetic information that helped it survive in a
particular environment from an invading virus particle (i.e. a virus vector), then that
bacterium would be selected to reproduce and grow at a faster rate than those organisms
that did not have this DNA advantage! The possibility exists that many different pieces
of DNA may have come together to give ancient bacteria specific qualities or traits that
other bacteria did not have. Examples of these traits might be the ability to capture
sunlight energy and make chemical energy (chloroplasts), or the ability to take pyruvate
and make ATP (mitochondria). That is virus pre-cursors that invaded “other” cells
became virus particles over evolutionary time (100,000 years perhaps) and eventually
were able to force the host cell to replicate more virus particles which not only
incorporated some of the host DNA into itself, but also burst out of the host cell and
infected other cells! When they infected other cells, they may have transferred pieces of
information (DNA) to the next host cell that made the cell better, worse, or had no effect!
The basic “life” cycle of virus particles relies on using the basic machinery of host
cells to replicate more virus particles. Virus has no Ribosomes or other organelles that
could allow them to isolate specific functions within their capsid, and this perhaps
prevents them from being more complex. However, the virus DOES have the ability to
use existing machinery to replicate and perhaps mutate at an incredible rate. This allows
the virus to “adapt” to new environments rapidly. Virus particles are also known to
replicate themselves and move genetic material from one organism to another, but
concomitantly they may take some
DNA from the host and transfer
random pieces of DNA from one cell
to another! This opens a huge door
to the concept of evolution!
A recent discovery of an
unusual virus might be the
“Mimivirus” (see picture to right).
Though the Mimivirus is larger than
some bacteria, it lacks ribosomes and
though reportedly “contain genes for
coding for nucleotides and amino
acid synthesis” (taken from:
http://www.microbiologybytes.com/
Mimivirus.html)
This virus has bi-lipid
which means it cannot make
membranes inside!
protein by itself nor process energy by itself.
Page 5 (Cont. Handout #22 AP Biology)
One of the most controversial hypothesis about the Mimivirus is not that it may be
associated with pneumonia (which some scientists believe), rather billions of years ago it
might have entered into a mutualistic symbiotic relationship with a Prokaryotic cell, and
became the Nucleus!
The most recent research use certain virus particles to “cause” specialized cells to
revert back to omnipotent status. This research has created controversy because the new
“stem” cell might be used to help diseased organs rebuild damaged areas (such as heart
muscle or nerve damage). However, knowing that virus particles can and do insert their
DNA randomly into to host DNA may disrupt oncogenes and therefore promote cancer
growth.
After reading the text and this handout, answer the following questions here and on your
scan-tron.
_____ 1.) Virus particles will attack (or attach to):
a.) any bacterial cell b.) any plant cell c.) any animal cell d.) cells with specific receptors
_____ 2.) Why is HIV more successful than “Ebola” virus? (Internet)
a.) because it is a lytic virus
b.) because it is a lysogenic virus
c.) because it does NOT kill host quickly
d.) because it DOES kill host quickly
e.) none of the above are correct
_____ 3.) What is a “phage”?
a.) it is a virus that kills its host rapidly
b.) it is a bacteria that kills virus particles rapidly
c.) it is a virus that can be BOTH lysogenic and lytic
d.) it is a virus that is larger than bacteria
e.) it is a virus that attacks bacteria
_____ 4.) How come the virus particle cannot live independently of a host cell?
a.) it has no ribosomes
b.) it cannot process energy
c.) it cannot make proteins
d.) all of the above are correct
_____ 5.) How do scientists grow virus particles in the laboratory (for production of
vaccines)? (Internet)
a.) they grow virus particles on cell culture plates
b.) they grow virus particles inside chicken eggs
c.) they grow virus particles inside human cells
d.) they grow virus particles in cell free nutrient media
e.) none of the above are correct
_____ 6.) Once a cell has been invaded by a virus – the host cell…
a.) cannot perform its normal function
b.) will die immediately
c.) will prevent other virus particles from entering
d.) all of the above are correct
Page 6 (Cont. #22 Virus AP Biology)
_____ 7.) Why is HIV such a successful virus in general?
a.) because it replicates itself exactly
b.) because it is able to process energy independently
c.) because it is able to make proteins independently
d.) because it makes many mistakes in replicating itself
_____ 8.) What type of HUMAN cell does HIV attach to (primarily)? (Internet)
a.) all immune cells b.) t-helper cells c.) t-suppressor cells d.) red blood cells
_____ 9.) How does HIV cause death in a human host?(Internet:hint- “full blown AIDS”)
a.) the virus produces toxins that paralyzes the respiratory system
b.) the virus cripples the immune system so it cannot fight off opportunistic infections
c.) the virus destroys all immune cells in the body
d.) the virus destroys all the red blood cells in the body
e.) all of the above are correct
_____ 10.) What is a “vector”?
a.) could be a virus that transfers genetic material from one organism to another
b.) could be a virus that moves its genetic material and perhaps the host genetic material
from one organism to another
c.) could be a “human host” carrier that transfers bacteria or virus to another organism
d.) all of the above could be correct
_____ 11.) What is a pathogen?
a.) it is a bacteria or virus that can cause disease in a suitable host
b.) it is a chemical that causes cancer
c.) it is when sunlight helps to cause skin cancer
d.) all of the above could be correct
_____ 12.) What is so special about the Mimivirus?
a.) it is larger than some bacteria
b.) it contains bi-lipid membranes inside of its capsid
c.) it MAY have been the symbiont that developed into a nucleus
d.) all of the above could be correct
_____ 13.) What are Mimivirus “Particles” missing that would allow them to make
protein?
a.) bi-lipid membranes b.) centrioles c.) ribosomes d.) genetic material
_____ 14.) How might viruses become an important tool in evolution?
a.) they can be vectors
b.) they can live independently
c.) they may have helped develop ribosomes d.) all of the above are correct
Page 7 (Cont. #22 Virus AP Biology)
_____ 15.) What is a parasite?
a.) it is an organism that lives off another organism, gives nothing back and often harms
the host
b.) it is an organism that neither helps nor hurts another organism but benefits from its
relationship
c.) it is an organism that benefits from a relationship and also benefits the other symbiont
d.) none of the above are correct
Answer the following questions on this handout only!
_____ 16.) What is the problem with using virus particles to revert specialized cells to
STEM cells (Internet)?
a.) it may not work
b.) it may promote cancer
c.) the virus is small and we cannot verify it attacks all cells d.) all above are correct
_____ 17.) Which of the following can be a pathogen to humans (mark all that apply)?
(Internet)
a.) CMV b.) EBV c.) avian flu d.) small pox e.) HIV
_____ 18.) Fuzeon and Miraviroc are anti-viral drugs that are in what class of viral
inhibitors? (Internet!)
a.) Non-nucleotide reverse transcriptase inhibitors (NNRTI)
b.) Nucleotide Reverse Transcriptase Inhibitors (NRTI)
c.) Fusion inhibitors
d.) Protease Inhibitors
e.) Integrase inhibitors
_____ 19.) What does AIDS stand for?
a.) Acquired Immune Deficiency Syndrome
b.) Acquired Integrase Deficiency Syndrome
c.) Active Immune Disease Syndrome
d.) Aliphatic Immune Disease Syndrome
_____ 20.) What are “Prions”? (pg. 405)
a.) living proteins that can infect cells and cause them to die
b.) non-living protein that cause similar proteins to change their configuration
c.) virus particles that cause cows to go insane
d.) virus particles that attack nerve tissue
e.) none of the above are correct
Page 8 (Cont. #22 AP Biology)
Answer the following questions on this handout only!
21.) Give three reasons why virus particles are not alive. Give three reasons why you
might consider virus particles to be alive.
22.) Speculate why virus particles are specific for host cells.
23.) Explain how HIV attacks a cell and explain why there is such a latency period before
AIDS occurs. (Internet/notes)
24.) Explain the difference between the lytic cycle and the lysogenic cycle of viral
replication in a host cell.
25.) If a virus stays exactly the same over thousands of years, it is thought to be
successful. Explain why such a virus does not have to mutate.
26.) Speculate why virus particles have not become more complex.
Date: _____________________________
Lesson Plan for Handout #22
A/P Biology
Objective: TLWD ability to explain the traits that may make virus alive and define traits
that show the virus particles are not alive. Students will also be able to explain the life
cycle of a virus, their specificity, and determine the difference between lytic and
lysogenic viral particles and be able to explain how virus particles invade humans, plants,
and bacteria when given handout #22.
Content: Virus particles, lifecycle, specificity, lytic, lysogenic, vectors- working for man?
HIV
Method: Power point, movie on HIV, white board, discussion.
Homework: Handout #22
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