Unit 4 – Student Guided Notes Structure of Viruses Discovery of the Virus

Many human epidemics were well documented and observed in history, but ________________________________________ _________________. The following 3 discoveries shaped our knowledge of viruses and disease

Jenner's Experiment (1700's). __________________________________________________________________. He discovered that milkmaids who contracted cowpox and recovered ________________________________________________ _________________________________________________. On the 14 May 1796, a young milkmaid called Sarah Nelmes came to see him with blister like sores. ___________________________________________ __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ which he would inject later. To test his hypothesis Jenner approached a local farmer and explained that if his theory was correct, the man's son James would never contract smallpox. Surprisingly, the farmer agreed. Jenner made two small cuts on James's left arm. He then poured the liquid from Sarah's cowpox sores into the open wounds which he bandaged. James got sick with cowpox but once recovered and exposed to smallpox he did not become ill with the smallpox disease. This was an extremely risky experiment, but James lived and Jenner had found a way to prevent smallpox.

Jenner called his idea " _______________________" from the word vaccinia which is latin for cowpox. Jenner also introduced the term _______________.

Tobacco Mosaic Virus (TMV) _____________________________________ _____________________________________ _____________________. The virus caused a blotchiness on the leaves of tobacco crops making them unmarketable and worthless. Solving this problem was a priority as tobacco was an important crop in these times. A German scientist, Adolf Meyer, suggested that Mosaic disease was contagious and proposed that the infectious agent was an unusually small bacterium that could not be seen with a microscope. He tested his hypothesis by successfully transmitted the disease by spraying sap from infected plants onto the healthy ones. Using a microscope, he examined the sap and was unable to identify a microbe. In 1897 a Dutch microbiologist, Martinus Beijerinck, _____________________ ______________________________________________________________________________________________________________________________________________He ruled out the theory that a filterable toxin such as bacteria caused the disease by demonstrating that the infectious agent in filtered sap could reproduce.

So what exactly is a Virus??? A virus is a ___________________________________________________ __________________________________________________________________________________________________________________________________________________________________. Viruses _______________________________________________________ and because of this feature are considered _____________________. In fact, viruses are ____________________________________________________. Viruses affect all types of cells, ____________________________________ _____________________________. For example, bacteriophages ________ ____________________________________, the tobacco mosaic virus infects only plants and the rabies virus only infects mammals. Viruses can be even more specific than this. Some human viruses even specialize in specific

tissue. Human immunodeficiency virus (HIV) affects specific types of white blood cells and the polio virus _____________________________________ ____________________________. Viruses are so specific because the capsid binds with _______________________ in the host cell's plasma membrane. If the receptors do not match then the virus cannot attach. Once attached to a cell, the virus _____________________________________________ within the host cell for its own purposes. Viruses and their relationship to host cells has led to the hypothesis that the ___________________________________________________________________________________________________________________________________. This statement suggests that viruses evolved after cells developed. If so, this means that new viruses are developing all the time. New viruses can develop _____________________________________________ __________________________. This means that antibodies produced by the body can work against one type of virus, but might not recognize the new mutated virus.

Virus Structure There are ______________________________ _____________________________ to viruses: 1. Proteins forms a structure called the coat or __________________. The capsid acts as the protective covering for the nucleic acid it contains. The proteins in the virus’ capsid must match the protein markers on the surface of the membrane of the cell it is trying to invade. As previously stated this feature is responsible for viral specificity. 2. Nucleic acids - All viruses contain either DNA or RNA, _______________________________ ______________________________________. This means that instead of using DNA to control the activities of the host cell ______________________________________ _____________________________________________________________

_______________________________________ which can then direct the activities of the host cell to reproduce viral particles. There are many different shapes and types of viruses but, because of the similarities between bacteriophages and animal cell viruses, the bacteriophage can be viewed as a model for animal cell viruses. The diagram above is of a typical bacteriophage. Head Region - _________________________________________________. The Tail - The Plug is a ___________________________________________ _____________________________________________________________ - The ______________________________________________________ to a bacterial host cell.

Viral Replication _________________ do not reproduce, they _________________________ _________________________________________________________________. Host cells ________________________________________________ __________________________________________________. Viruses are specific to a particular host cell because part of the capsid binds to the receptor on the host cell's plasma membrane in a lock and key fashion. The virus then will inject its viral nucleic acid into the host cell and ____________ _____________________________________________________________ _____________________________________________________________________________________________________.

Replication of Bacteriophages Bacteriophages are viruses that are parasitic to bacteria. These phages must use bacteria to replicate. Phages have two types of cycles. In _____________ ____________________________ the virus is replicated within the host cell resulting in ____________________________________________________ releasing all of the newly formed virus particles. In _____________________ the __________________________________________________________ _____________________________________________________________ __________________________________________________________________________________________________________________________

____________________________________________________ sometime in the future.

Reproductive Cycles Lytic Cycle There are five key stages to the lytic cycle.

1. _________________________ - Capsid combines with the bacteria's receptor in a lock and key fashion.

2. _________________________ - Enzymes from the virus start to eat away the bacterial cell wall and will inject its viral DNA into the bacterial cell.

3. _________________________ - At this stage the virus inactivates the bacterial genes and takes over the metabolic functions to produce copies of DNA and produce the capsid.

4. _________________________ - During this stage, the viral DNA and capsids are put together.

5. ________________________ - Lysosomes are made and produce hydrolytic enzymes to eat a hole in the cell wall of the bacteria. At this time, the cell will lyse and the newly formed viruses will leave the host cell.

Lysogenic Cycle _________________________________________________________, the _________________________________________________________, but ____________________________________________________________. During the lysogenic cycle, the phage becomes a prophage that is integrated into the host genome (DNA). At a later time, the phage may start the lytic cycle. When a virus is latent i.e. _______________________________________, it is called a prophage. ___________________________________________________________________________________________________________________________________________________________________________. Examples of lysogenic Viruses: Herpes, Hepatitis, HIV

Retroviruses Retroviruses are viruses that have the _____________________________. These viruses contains an enzyme called ________________________ ___________________. This enzyme _____________________________ _____________________________ (in other words, it allows the RNA to make DNA). ____________________________________________________________ __________________________________, which can hide in the host's DNA. ___________________________________________________________________________________________________________________________________________________________. An example of a retrovirus is HIV and some that cause cancers. Are Viruses Alive? What are the characteristics of life? How do we define whether something is living or not? Living things….

1. _______________________________________________.

2. _______________________________________________.

3. Require a constant energy supply.

4. ________________.

5. ____________________________________.

6. _______________________________________________.

7. Contain enzymes.

8. Can move.

So, are viruses living or nonliving? The following table gives evidence to support each theory.

Living

Non-living

Viruses have DNA or RNA and protein. No non living thing carries nucleic acid

______________________________________________________

__________________________________________________________ (slightly different variations)

Viruses do not eat

Viruses display continuity

Viruses do not grow

Viruses have the ability to reproduce One generation follows another

___________________________ ___________________________

Viruses contain enzymes

Viruses do not reproduce on their own. Viruses are parasitic

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Viruses do not move

Viruses _________________________________________________things as they do not exhibit many of the characteristics of life. Viruses are not classified in the classification system because they are ______ ___________________ and should not be classified with organisms that are cellular. Viruses are generally smaller than 200 nm in diameter and can be crystalized.

Viral Diseases We now know that viruses are considered pathogens that cause disease. We know that many of these diseases are specific to a particular type of host cell

and that viruses are not considered living as they require this host cell to reproduce. We also know that viruses cause a large variety of diseases. Some __________________________________________ while _________ ___________________________________________________________________________________________________________________________________________________________________________. Some new antiviral medications are being developed but are only used in special

circumstances at this time. Viral pathogens are newsworthy. You may recognize the ones in the list below. You will notice that there is a lot of variety in the structure and function of these viruses. This variety is not a surprise as viruses have been evolving for a very long time along with the cells they infect.

The photo above is a micrograph of an Adenovirus that causes the common cold. You know the symptoms. Photos below are of Smallpox which causes high fever and the formation of small blisters on the skin. _______________________________ _____________________________________________________________(1970's). Let's hope it stays that way as vaccinations ceased in the 1980's.

Photos below are of the Polio virus which is transmitted through direct contact and feces and the IRON LUNG. Polio destroys nerve cells and causes paralysis. It may well be the next viral disease eliminated by a vaccine.

Hanta Virus Hanta virus _____________________________ ______________________________________ _______________. The result is ___________ ______________________________________ _____________________________________. There is no vaccine so avoid contact with mice! West Nile Virus West Nile virus is transmitted_____________________ ___________________________________________. The virus ___________________________________ (encephalitis). There is no vaccine so avoid contact with mosquitoes. _________________________________ ___________________________________________. HIV (Human Immunodeficiency Virus) __________________________________________________________________________________________________________________________

___________________________________________. Transmission of the virus is _______________________ _________________________. It is estimated that 50 million people are infected worldwide. There is no vaccine but there are effective drugs that can slow the disease but not cure it. Ebola

Ebola was first recognized in 1976. It is ______________________________ _________________________________________ _________________________________________ _________________________________________ ________________________. There is no vaccine but outbreaks have been controllable (so far). This virus is often the source of inspiration for movies such as "Outbreak"

Preventing Viral Diseases Antibiotics are _________________________________________________. Antibiotics are designed to disrupt the metabolism of organisms. They work on bacteria but ___________________________________________________ __________________________________________________. The best way to stop viral infections is to prevent them from getting into the body to find a host cell. The term ________________________ is often used to describe the degree to which a particular pathogen is infectious. The human body has 3 major lines of defense against disease caused by viruses and bacteria. The Primary line of defense is made up ___________________________. These barriers include: skin, hair, earwax, boogers, saliva, stomach acid, cilia in the throat, mucus, tears, oil, etc.

The first line of defense is almost always enough to stop invaders. However, _____________________________________________________________ _________________________________________ and the pathogens are able to move inside the body. When this happens _____________________________________________ __________________________________________________________________________________________________. These are the secondary and tertiary lines of defense. Secondary line of defense is made up of Phagocytic white blood cells that deactivate and then engulf the viruses destroying them. When the secondary line of defense cannot destroy the invaders the Tertiary line of defense is activated. The tertiary line of defense is made up of ___________________________________________________________ __________________________________________________________________________________. The antibodies find the chemical signal the antigen is excreting and latches on to it. Different pathogens have different markers. Antibodies are made specific to each marker. B-Cells (____________ ________________________________) release antibodies. (They tag the incoming virus for destruction). ____________________________________ ______________________________________________________________________________________________________________. Viruses are destroyed later by phagocytic white blood cells. Additional defense against viruses ____________ are produced by virus _______________________________ _______________________________________________________________________________________________________________________________________. Interferons slow viral infection and allow WBCs and antibodies to respond. And __________________________ are chemicals that ____________________ (cell-eating WBCs) in the blood. Pathogens are engulfed and digested by the phagocytes.

Achieving Immunity _______________________________ are used to produce immunity against pathogens. It is the process of infecting a person with a __________________

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