Viruses

1. According to the article you read yesterday, do scientists consider viruses to be alive? Why or why not?

Discover of viruses Martinus Beijerinck: Dutch scientist who said that disease is caused by tiny particles in juice. Called them viruses. Latin for poison. Wendall Stanley: isolated crystals of the tobacco mosic virus. Dmitri Ivanovski: for tobacco mosiac in liquids extracted from infected plants.

VIRUSES Virus: infectious particle that contains DNA or RNA surrounded by a protein coat that can only reproduce in a host cell. Latin for “poison”.

At the boundary of life, between the macromolecules (which are not alive) and the prokaryotic cells (which are), lie the viruses and bacteriophages (phages). These twilight creatures are parasites responsible for causing many diseases in living things (herpes and HIV in humans, for example). Viruses are found everywhere. Viruses consist of a core of nucleic acid, either DNA or RNA, and a protective coat of protein molecules and sometimes lipids. Viruses - Are viruses alive? Scientists are still arguing!!!

In isolation, viruses and bacteriophages show none of the expected signs of life. They do not respond to stimuli, they do not grow, they do not do any of the things we normally associate with life. Strictly speaking, they should not be considered "living" organisms at all. However, they are more complex than a lifeless collection of macromolecules and they do show one of the most important signs of life: the ability to reproduce at a fantastic rate but only in a host cell.

Characteristics of Living Things Respond to stimulus: virus respond when a cell is near and attaches. Cells: Not cells as we know them Adapt: The viruses do mutate to become stronger but only in a host cell. Reproduces: only in a host cell Energy: Uses energy of the host DNA: Yes they do have their own Grow and develops: Only in host Viruses are parasites that can only perform certain characteristics in host cells. Host: The cell that the virus attaches and uses their DNA and resources.

Viruses consist of a core of nucleic acid, either DNA or RNA, and a protective coat of protein molecules and sometimes lipids(capsid). PARTS OF A VIRUS CAPSID: Protein coat Surrounding the DNA.

Size and Shape of Viruses Viruses come in all shapes sizes. You can only see them with a microscope. 3 shapes of viruses 1.Enveloped – round with spikes( flu viruses) 2.Helical – Long narrow coiled shape( rabies) 3.Polyhedral- many sides(foot and mouth disease)

The different proteins that make up the capsid determines the shape of the virus.

Attacking the host The size and shape of a virus determines which cells or host they can attack.

Attacking Host The virus will attach itself to the host cell. It will then shoot its DNA into the host cell. The virus is a parasite that uses the host cell for its energy and reproduction. It is a little different if it is a bacteria cell or eukaryotic cell.

Bacteriophages attack bacteria (prokaryotes) viruses attack eukaryotic cells(have a nucleus). viruses attack eukaryotic cells(have a nucleus). Viruses and bacteriophages invade cells and use the host cell's machinery to synthesize more of their own macromolecules. Difference between a bacteriophage and a virus

Once inside the host the bacteriophage or virus will either go into a Lytic Cycle - Lytic Cycle Lytic Cycle destroying the host cell during reproduction. or It will go into a Lysogenic Cycle - a parasitic type of partnership with the cell

Lysogenic Cycle The virus COMBINES its DNA with the host DNA producing a Prophage. The cell is not destroyed. As new cells are made, it will be the virus and not host cell. Cell not destroyed.

LYSOGENIC CYCLE Both:

The Lysogenic Cycle

Lytic Cycle In the lytic cycle, the virus takes over the hosts DNA and grows its own. It grows its own DNA and new viruses. The virus uses the energy of the host cell. When it is full, the host cell explodes and releases new viruses.

LYTIC CYCLE

The Lytic Cycle

A provirus is a DNA virus that has been inserted into a host cell chromosome.

A retrovirus injects the enzyme, reverse transcriptase into the cell to copy viral RNA into DNA.

HIV is a retrovirus injecting the enzyme, reverse transcriptase into the cell to copy viral RNA into DNA.

Viruses are host specific – a protein on the surface of the virus has a shape that matches a molecule in the plasma membrane of its host, allowing the virus to lock onto the host cell.

HIV doesn’t target just any cell, it goes right for the cells that want to kill it. “Helper" T cells are HIV's primary target. These cells help direct the immune system's response to various pathogens.

HIV undermines the body's ability to protect against disease by depleting T cells thus destroying the immune system. The virus can infect 10 billion cells a day, yet only 1.8 billion can be replaced daily.

After many years of a constant battle, the body has insufficient numbers of T-Cells to mount an immune response against infections. At the point when the body is unable to fight off infections, a person is said to have the disease AIDS. It is not the virus or the disease that ultimately kills a person; it is the inability to fight off something as minor as the common cold.

The vaccine is administered. It contains weakened or dead forms of the disease 1.The immune system identifies these foreign substancesimmune system (viruses and bacteria), also known as antigens.viruses 2.Once antigens are identified, the immune system develops proteins that circulate in the blood. Theseblood proteins are called antibodies. They fight the infection by killing the antigens. Antibodies are made by white blood cells called lymphocytes, also known as B cells. The main purpose of B cells is to create antibodies to fight infection. 3.The body stockpiles these antibodies so they are available to fight off the disease if exposed later on. Unfortunately, antibodies are disease-specific, so previously acquired chickenpox antibodies will be useless if faced with other diseases.

Jenner was operating on the now widely accepted principle that once a person catches a certain disease, he or she is immune to it for the rest of their life. For example, once you've had the chickenpox, it's extremely unlikely that you'll ever catch it again. This is because your body, when exposed again, will recognize the disease and fight it off. The beauty of vaccines is that they help the body develop disease- fighting abilities without making you sick. Vaccines accomplish this amazing feat by tricking the body into believing it already has the full-blown disease. Here are the steps in this process, known as the "immune response":

Vaccine-preventable Diseases Anthrax Cervical Cancer Diphtheria Hepatitis A Hepatitis B Haemophilus influenzae type b Human Papillomavirus Influenza Japanese encephalitis Lyme disease Measles Meningococcal Monkey pox Mumps Pertussis Pneumococcal Polio Rabies

Rotavirus Rubella Shingles Smallpox Tetanus Typhoid Tuberculosis Varicella Yellow Fever Source: CDC v