virus

VirusTiny 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

1st 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

• Instead of joining the cell, the virus injects the DNA/RNA into the host cell

Virus Infection Type 2: Bacteria

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 genome2) It hangs out while everything is okay3) 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 ShapesAn 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 InfectionsHow 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 deepestLag 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