Mr. Wright, 2011

Section 19.2

 A virus is a nonliving particle made up of nucleic acid and a protein or lipid-protein coat.

 They reproduce, infect, and adapt. So why are they non-living?

  Cannot move outside of a host.

Cannot reproduce without the aid of a host.

  Cannot produce their own energy (ATP).

Not made of cells.

   Spread by air, water, food, bodily fluids, and other organisms.

Outside of a host cell, viruses have no control over its movements.

A vector is an intermediate host that transfers a pathogen or parasite to another organism. Examples: fleas, mosquitoes, ticks

  Viruses infect all living organisms.

They cause many diseases and are useful tools for genetic research.

 We’ll talk about why later!

    The study of viruses = virology There are over 2000 types of viruses.

Viruses are about 100 times smaller than bacteria.

Viruses come in many different shapes and sizes.

  Let’s draw one!

A virus is made of 3 parts:  Genetic Material  The genome can be either DNA or RNA.

  Protein Coat  This protein coat is called a capsid.

Lipid Envelope   Some viruses have a layer of fat around the outside.

Not all viruses have one – useful for classifying into groups!

 Like living things, it is useful to put viruses into groups based on several factors.

   Is their genetic material DNA or RNA?

  Is it single stranded or double stranded?

Is it linear or circular?

What is the shape of their capsid?

 Can be helical, spherical, or icosahedral Does the virus have an envelope?

  A bacteriophage is a special type of virus that infects bacteria.

They have a very specialized shape.

 Bacteriophages use these specialized shapes to inject their genome into bacteria – it’s kind of like giving a shot.

Section 19.2

 Viruses are obligate intracellular parasites.

 What do you think that means? (break it down!)   Obligate – required Intracellular – inside a cell  Parasite – something that lives off of something else  Simply put, a virus has to live inside of another cell in order to reproduce .

 Viruses first need to recognize a host cell before they can infect it.

 They do this using a “Lock-and-key” method.

 The virus has to match up and “fit” a specific cell in order to infect it – like a key that only fits in one lock.

   Once a virus has found a host cell, it injects its genome inside it and the genome forms a circle.

Viruses need to make 2 parts to reproduce:  Make new viral proteins (capsids)  Make new viral genetic material There are two pathways for viral replication – the lytic cycle, and the lysogenic cycle.

 The viral genome takes control of the cell, producing many more viruses. The cell then bursts (lyses), releasing all new viruses.

   The viral genome combines with the host genome, where it “hibernates” for awhile.

Every time the host cell divides, it copies its genome. Every new cell is infected with the viral genome.

The virus eventually enters the lytic cycle.

  Scientists can use viruses for good – we can inject any gene we want inside of a cell.

As we’ve seen, if a virus goes through the lysogenic cycle, this new gene combines with the host cell’s genome.  We’ve just inserted a gene!

 How do we use this? What kind of genes can we add to organisms?

   Genes that make crops with higher yields.

Genes that add vitamins and minerals to food.

Genes that make livestock grow bigger.

Section 19.3

 Chickenpox  Symptoms include fever and skin rash.

  Itchy boils all over the body.

Spread through direct contact and through the air.

  Most people get chickenpox as a kid. Once you’ve had the virus, you develop a lifelong resistance to that strain!

HOWEVER, the virus can reemerge as you get older, making you sick again. This is called shingles. The older you are, the worse it is.

    AKA the flu.

Causes fever, muscle pain, headache, weakness, and general discomfort.

Spreads through the air and through bodily fluids.

Mutates very quickly!

   The fact that influenza mutates so fast is what leads to all the different strains out there.

Examples:  Swine Flu    Bird Flu/Avian Flu Horse Flu Dog Flu Named after the animals they’re most commonly found in.

  An emerging disease is a disease that seems to come out of nowhere to reek havoc in a short amount of time.

Examples:  Ebola   West Nile virus Any zombie movie ever.

  Some viruses can lead to cancer.

 Cancer – cells dividing uncontrollably, forms a lump called a tumor Example: HPV (Human papillomavirus)  Cervical Cancer

 AIDS = Acquired Immunodeficiency Syndrome  Caused by HIV.

 HIV = Human Immunodeficiency Virus

 HIV infects the bodies immune system, hurting the bodies ability to fight other infections.

 An opportunistic infection is an infection caused by something that wouldn’t normally cause disease in a healthy immune system.

 These infections cause serious problems in AIDS patients, eventually resulting in death.

  HIV can be spread in three ways:  Sexual contact  Blood  From mother to fetus Treatments can slow the course of the disease, but there is no cure or vaccine.

 AIDs is a pandemic – there are currently 33.2 million people worldwide with the disease.

 Main way to combat AIDs is awareness.

 HIV is a retrovirus.

 A retrovirus is a special type of virus that has RNA as its genetic material and contains an enzyme called reverse transcriptase.

 Reverse transcriptase transcribes DNA from RNA.

 Viroids  Viroids are the smallest known particles able to replicate.

  It’s basically a virus without a capsid – just a single circular strand of RNA.

They infect plants and damage entire crop fields.

 Prions     A prion is basically just a capsid – a virus without a genome.

They convert normal brain proteins into other prions.

As prions accumulate in a cell they clump together and lead to cell death.

Mad Cow Disease is a prion disease.

Solving the Puzzle

 Some viruses, such as influenza and HIV, mutate very fast.

 Fast viral mutations make treating the viruses difficult, because they are constantly changing.

 The immune system begins to target the original viral strain, but not the new mutant strain yet.

 All of the old strain viruses are destroyed, while the new strain is unaffected.

 The new mutant strain becomes the dominant strain within the body, then starts to spread.

 Vaccinations  A vaccine is a solution containing a harmless version of a virus, bacterium, or a toxin   The immune system learns to recognize and kill harmful versions.

Vaccinations are highly effective

 Vector Control  What are some examples of a vector?

  An important part of preventing viral disease is the control of animal vectors.

If you wipe out what spreads the disease, you wipe out the disease.

 Drug Therapy  Would an antibiotic be able to stop a viral disease?

 It is difficult to design a drug that stops the virus without harming the host cells.