Transcript Virus

Virus
Tiny non-living particles
Greek for poison
Big Question: Are viruses alive?
• Characteristics of living things:
• Made of one or more cells
• Grow
• Reproduce
• Responds to the environment
• Obtains and uses energy
• Gets rid of wastes
Basic Characteristics
• Up to 100 times
smaller than bacteria
• Function is to
reproduce
• Must have host cell to
reproduce
• Named after the
disease they cause or
tissue they infect
Structure
• Inner core of nucleic acid (DNA or RNA)
• Surrounded by a protein coat
• Protein coat gives viruses many different shapes
Flu
HIV
Ebola
Common Diseases Caused by Viruses
• Cold sores/herpes
• Warts
• Mumps
• Smallpox
• Rabies
• Measles
• HIV
• Hepatitis
• Flue
• Common Cold
Methods of Reproduction
• Lytic Cycle and Lysogenic Cycle
st
1
Method: Lytic Cycle
• Attaches and enters the host cell through cell
membrane
• Replication of the virus
• Host DNA destroyed
• Virus DNA is replicated and proteins are made using
the host cell
• Assembly- new virus parts are put together
• Lysis (cell death) and release of new virus
particles
• Host cell explodes and lets out new viruses
• http://www.youtube.com/watch?v=Rpj0emEGShQ
Virus binding to host type one: human infection
1) Receptors from the virus ensure they bind to the right kind
of host
2) The virus rolls along the surface until it stops, the fuses
with the cell
3) The viral DNA or RNA enters the cell
Virus Infection Type 2: Bacteria
• Instead of joining the cell, the virus
injects the DNA/RNA into the host
cell
Viral Replication
• Virus DNA hijacks the hosts replication proteins
• Host cell begins to make new virus nucleic acids and protein
• The parts of virus self assemble and are shipped out of the
cell, or build up and the cell bursts
• Why might a virus want to build up until a cell bursts, rather than
simply export out of the cell as they are made?
Lysogenic Cycle
• Attachment and entry into the cell through the
cell membrane
• Provirus formation
• Viral DNA becomes part of the host chromosome
• Cell Division
• Virus is inactive but is replicated each time the host
cell divides
• Provirus leaves chromosome
• Virus enter lytic cycle
• Host cell slowly releases new viruses
RetroViruses: The First Sleeper
Agents
1) Viral DNA incorporates into host genome
2) It hangs out while everything is okay
3) Bails and blows the whole cell up when
things are no longer okay
Viral Structure: Bacteriophage
• Head- hold the “brains” (DNA/RNA and
proteins)
• DNA/RNA- nuclear membrane to code for
proteins
• Internal Proteins- Allows the virus to gain a
foothold once inside the cell
• Tail Sheath/Neck- Structural, help with
assembly and often have other
proteins attached (some viruses can go
“dormant”)
• Tail fibres- for attachment to host
• End plate- Attachment to the host and
penetration of host membrane
Flu Virus (Animal Virus)
• Capsid- protein coat
• Lipid Envelope- like a cell membrane,
helps protect virus from immune
system
• Hemaglutinin- attachment to host
cells
• Neuraminidase- helps to get virus out
of host cell after replication
Major Viral Shapes
An array of viruses. (a) The helical virus of rabies. (b) The segmented helical
virus of influenza. (c) A bacteriophage with an icosahedral head and helical
tail. (d) An enveloped icosahedral herpes simplex virus. (e) The unenveloped
polio virus. (f) The icosahedral human immunodeficiency virus with spikes
on its envelope.
• Do questions page 360 #1-3
• Copy figures 17-5 and 17-6 on the page provided and
label the different stages. Compare what the virus
does in both stages at the bottom of the page.
• Do Problem Solving Lab (hand in when complete)
Viral Infections
How we fight the good fight
Viral Specificity
• Viral Specificity- viruses have adapted to infect certain
species
• E.g. Pigs, Birds, and Humans are infected by similar flu
viruses. Dogs are not.
Reasons for Viral Specificity
• #1 Reason: proteins on the virus only bind to specific
receptors
• E.g. Polio binds to nerve cells, mumps to salivary glands,
hepatitis to liver cells… these proteins tend to be highly
variable species to species
• The tail fibers in bacteriophages, or the capsids for animal
viruses, bind to specific proteins
Your Bodies Defense
• Up until now, we only discussed how the viruses used and abused
us… well it is time we fight back!
Primary Line of Defense
• Skin- provides a barrier between us and them
• Mucous membranes- protect in a similar way to skin, except mucus is
typically transported elsewhere
• Tears- one of the first antibacterial substances (but many viral
infections get in through the eyes so stop touching your face!)
• Ear wax- produced by the body and traps the invaders and keeps
them from getting in
Secondary Line of Defense
• Innate Immune Response
• Non-Specific (ie. Will attack anything that isn’t you)
• Phagocytic white blood cells engulf viruses
• Natural killer cells
• Kill infected cells
• Absence of self- ie. Viral proteins showing up on the outside of a cell
Tertiary Line of Defense
• Adaptive Immune Response
• 2 Types of White blood cells
• B-Cells- produces antibodies that stick to viruses, act like a large
group of 5 year olds attacking a grown man
• T- Cell
• Helper- Run around telling cells what to do “You- Produce antibodies.
You! Eat something. No not that! Bacteria/Viruses!”
• Killer- aka Cytotoxic T lymphocytes- from the previous picture, finds
infected cells and puts them down (triggers apoptosis)
Adaptive immune Response (in a nutshell)
• Innate immune response eats something infectious and wears it
around telling other cells “this is one bad mambajamba”
• If it runs into a B or T cell with a receptor that matches the
viral/bacterial protein, that cell kicks it into high gear, replicating a
ton, and starts kicking butt and taking names
The first cut is the deepest
Lag period while B-Cells reproduce
and make antigens (3-15 days)
The second time though…
• Memory B-cells floating around recognize that jerk from last time
• Antibody numbers are way higher
• Response is much faster (3-7 days)
How do you think vaccines work?
• Read pages 973-975 – Summarize what a vaccine is and how it works
• Do questions page 971 # 1-4 and page 976 #1-3
• Do Problem Solving Lab