Download 1. Is a virus ALIVE?

WHAT IS LIFE?
THE Question in Biology,
time to consider this in more detail.
Remember that…
For anything to be considered “alive” it must have
ALL the Fundamental characteristics & at least
SOME of the Common characteristics.
This definition of life does create a few problems…
...is a VIRUS alive?
Virus
Particles
We know that we ‘catch’ viruses, they make us sick and
our bodies ‘kill’ them off to make us better.
But what exactly is a virus?
VIRAL STRUCTURE
Protein Coat
- a container or bag to hold material
- determines shape of virus
Genetic Material
- small piece of genetic material
- can be DNA or RNA
- the “brain”
External Proteins
- used for recognition, attachment
- may differ in the same type of virus
DNA - storage molecule for all instructions a cell may need
RNA - working copy of one or two instructions to be used by cell
VIRAL LIFE CYCLE
Viruses invade cells & force them to make more viruses.
1. Getting Into the Cell
T4 phage
Bacteriophage
- attaches to cell
surface & injects
genetic material
Smallpox
Animal Virus
- triggers cell to
engulf or ‘eat’
virus (endocytosis)
Tobacco Mosaic
Plant Virus
-through a cell wall
injury
-or when pollination
occurs
2. Taking Over
DNA virus - two types
(a) Lytic Cycle
- very fast, destroys cell DNA & replaces it with viral DNA
- viral symptoms are immediate
Small pox virus
-muscle aches and joint pain are immediate
-followed soon by organ inflammation
and failure and then death
1. Attachment — Virus attaches to the cell wall at a receptor
site.
2. Penetration — The cell wall is weakened by the viral
enzymes, and the deoxyribonucleic acid (DNA) of the virus is
injected into the host cell.
3. Synthesis — The DNA of the host cell is inactivated, and the
viral DNA takes over making viral proteins and viral nucleic
acid.
4. Assembly — Viral coats of protein capsids are assembled
with the nucleic acids filling the cell with new virus particles.
5. Lysis – Enzymes dissolve the host cell membrane from
within. The cell then bursts open.
6. Release — The newly formed virus particles are released,
free to infect other bacterial cells.
The lysogenic cycle proceeds in the same way
as the lytic cycle except the nucleic acid
becomes part of the host cell's DNA, and it
does not immediately take over host cell.
The actual replication is delayed. Viruses
that do not cause an immediate infection are
referred to as temperate or latent. They exist
as a prophage and can be dormant for
years. The virus can become active (virulent)
years later.
Stimuli that bring about their activation
include exposure to environmental factors
like radiation and chemicals.
(b) Lysogenic Cycle
- slow, combines its viral DNA with cell DNA
- viral symptoms are delayed
Human Herpes Simplex 3
- causes cold sores
- can hide in nerves & reappear
- transmitted by close contact
RNA Virus - two types
(a) Simple RNA
- takes over cell functions directly
- avoids cell DNA entirely
- slow or fast life cycle
eg. flu
Influenza
- small, airborne virus that mutates every 6-12 months
- infection & recovery takes 72 hours
- symptoms congested lungs & nose, nausea, headache, fever,
aching joints
- Spanish Flu of 1918 killed over 25 million people ages 15 - 35
Should you get a flu shot?
(b) Retrovirus
- uses an enzyme to rewrite cell’s DNA with the viral RNA
- enzyme makes frequent mistakes thus has a
very high mutation rate
- long, slow life cycle
HIV
- long life cycle with fast mutation rate
- very fragile, air is lethal in 2 s
- causes in first 1-2 weeks flu like symptoms
- causes after 1 month lack of energy, weight loss,
frequent fevers, skin rash, short term memory
loss, inflamed pelvic area, frequent infections,
rare cancers (Karposi’s sarcoma)
Should everyone in a high risk
group be tested for the virus?
3. Getting Out
Cell Lysis
- virus particles build up inside cell
- cell eventually bursts open
- cell is completely destroyed
- very common
Exocytosis
- virus is exported out of cell
- no damage to cell structure
- can continue to make viruses
- very rare
Interesting Facts...
No two viruses can infect the same cell…Why?
After taking over, a virus will change the structure or coating
of the outside of the cell so other viruses can’t get in.
Bacteria are very resistant to infection by viruses…Why?
Bacteria have Restriction Enzymes inside them.
These act like scissors to “cut up” any foreign DNA or RNA
before it can do damage.
1. Is a virus ALIVE?
Common Characteristics
1. move
2. respond to stimulus
3. can’t develop (grow)
4. contain complex components
5. die (destroyed)
Additional Characteristics
1. not made of cells
2. no metabolism
3. Can’t reproduce without
infecting a living thing
4. Can reproduce within a host
and kill it
5. have DNA or RNA which is
passed onto “offspring”
6. no homeostasis
Since viruses don’t have all of the additional characteristics
of life, and they must rely on other living things,
they are NOT QUITE ALIVE.
2. Characteristics of Viruses
• All viruses are parasitic
and cannot live
independently
• They can invade all cell
types (e.g. plant viruses
and animal viruses)
• They must use the energy
of other cells to “live” and
reproduce
a flu virus has 8 genes inside a
protein coat, the pink and
yellow spikes represent the
proteins hemagglutinin and
neuraminidase
Prion Diseases:
Sheep - Scrapie
Elk - Chronic Wasting Disease
Mad Cow Disease
Infection:
- from pasture or feed
- genetic disorder?
Human Examples:
Creutzfeldt-Jakob Disease (CJD)
Vacuoles
Symptoms:
loss of motor control, dementia,
paralysis, wasting and eventually death
Infection:
- from food (eating infected animal)
CJD Brain
- from working with infected animals?
- genetic disorder?
PRIONS:
definitely not alive
- a small piece of protein that can infect cells & cause disease
- resist destruction or inactivation by procedures that
stop DNA or RNA viral infections
- most cause some type of spongiform encephalopathy
(creates large vacuoles in the brain causing damage)
Nanobes: What are they?
Odd-shaped things
seen under high
magnification
[35,000 x]
Discovered by an
Australian geologist
Dr. Phillipa Uwin in
1996
very, very small [0.05
– 0.2 mm] smallest
bacteria is 1.0 mm
Nanobes:
Are they alive?
Researchers believe they are too small to
have the necessary ingredients for
independent life
But, they seem to multiply on their own.
Evidence that there is DNA in them.
Composed of biological material (Carbon,
Nitrogen, Oxygen)
Answer – we don’t know !!!
Credits:
“CJD” Online. Internet. 29 November 2012. (www.uiowa.edu/~c064s01/_nr388.htm)
“Diabetes Research” Online. Internet. 29 November 2012.
(www.pitt.edu/~biohome/Dept/_Frame/diabetesresearch.htm)
“exn.ca Discovery Channel” Online. Internet. 29 November 2012. (exn.ca/stories/1997/_05/02/02.asp)
Johnson, Jeff. “Biological and Medical Visuals” Online. Internet. 29 November 2012.
(www.hydridmedicalanimation.com/_pages/aids.htm)
“Journal of Molecular Evolution - Reciprocal relationship between stem-loop potential and
substitution density in retroviral quasispecies under positive Darwinian selection.”
Online. Internet. 29 November 2012. (post.queensu.ca/~forsdyke/_hiv01.htm)
“Keeping Wisconsin Deer Healthy” Online. Internet. 29 November 2012.
(www.dnr.state.wi.us/…/_issues/deerhealth.htm)
“Laymand Land” Online. Internet. 29 November 2012. (www.mindspring.com/~cinque/ql.htm)
“Prion Diseases” Online. Internet. 29 November 2012. (www-micro.msb.le.ac.uk/335/prions.htm)
Credits continued:
Prion Image. Online. Internet. 29 November 2012. (www.bse.tc.pl/czyn.html)
Scrapie Image. Online. Internet. 29 November 2012.
(www.verbraucherministerium.de/…/rep1-97/prion.html)
“The Big Picture Book of Viruses: Herpesviridae” Online. Internet. 29 November 2012.
(www.virology.net/Big_Virology/_Bvrnaortho.html
“The Big Picture Book of Viruses: Orthomyxoviridae” Online. Internet. 29 November 2012.
(www.virology.net/Big_Virology/_Bvrnaortho.html
“Virus Ultra Structure” Online. Internet. 29 November 2012.
(www.uct.ac.za/depts/mmi/_stannard/virarch.html)
Withrow, Kira. “Bacteria” Online. Internet. 29 November 2012.
(www.hometaught.com/kira/_docs/K_Bacteria.htm)
Nanobes-Origins Feb 9 2013
“More evidence for Nanobes”
http://www.microscopyuk.orhttp://www.abc.net.au/science/news/space/SpaceRepublish_444160.htmg.uk/mag/in
dexmag.html?http://
www.microscopy-uk.org.uk/mag/artdec99/nanonew.html