Viruses Discovery of Viruses Berijerinck Wendell Stanley Edward Jenner (1897) coined the Latin name "virus"  meaning poison for  the substance infecting tobacco plants Wendell Stanley (1935) crystallized sap from tobacco leaves infected with Tobacco Mosaic Virus (TMV) first person to see virus found virus was made of nucleic acid & protein Edward Jenner (1796) developed smallpox vaccine used pus from cowpox

Viruses Discovery of Viruses - Continued Louis Pasteur Sabin Salk Developed second vaccine against anthrax Developed third vaccine against rabies Used dried spinal cord of a rabbit Sabin Developed vaccine against polio that contained live virus Given orally Salk Developed vaccine against polio using killed virus Given as shot

Viruses Virology - study of viruses Deadly viruses are said to be virulent Viruses couldn't be seen until electron microscope invented Viruses cause disease by Killing cells Changing the rate of mitosis (warts, tumors, and cancer)

Wendell Stanley and Leaf with TMV

Viral Characteristics Not living organisms Noncellular Consist of a nucleic acid core (DNA or RNA) a protein coat called the capsid Some have a plasma membrane Capsid made of protein subunits called capsomeres Cannot grow or replicate on their own (inactive particles)

Viral Characteristics Can only reproduce inside of a living host cell using its raw materials & enzymes Lack ribosomes & enzymes needed for protein synthesis or metabolism Are extremely small particles ranging from 10 - 1400 nanometers on average Some can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, Ebola)

Viral Characteristics Some may also cause cancers such as leukemias Virus free cells are rare Highly host specific (only infect certain cells) Referred to as phages Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA Viruses  DNA & RNA viruses are subdivided by capsid shape & whether they do or don't have an envelope

Viral Structure DNA or RNA core surrounded by protein sheath called capsid Nucleocapsid  includes the viral nucleic acid & its capsid Some form lipid rich covering around capsid called the envelope Envelope usually formed from host cell membrane Envelope may have spikes to help chemically recognize & attach to the host cell

Viral Structure TMV is helical Adenovirus & polio viruses are icosohedral (20 sided)

Viral Structure T-phages have a head and a tail

Bacteriophage or T-phage Among the most complex viruses Attack bacterial cells Composed of a icosohedral head, tail, base plate, & tail fibers Long DNA molecule is inside the head  Tail helps inject the viral DNA into host cell Tail fibers used to attach to host

Retrovirus Contain RNA Have an enzyme called reverse transcriptase which helps use the RNA to make DNA Use the host cell's ribosomes & raw materials to make viral proteins Cause some cancers & AIDS HIV Virus

Lytic Cycle Phases of the Lytic Cycle of a Virulent Virus: Absorption: Virus attaches itself to the cell. Entry: Enzymes weaken the cell wall and nucleic acid is injected into the cell, leaving the empty caspid outside the cell. Many viruses actually enter the host cell intact. Replication: Viral DNA takes control of cell activity. Assembly: All metabolic activity of the cell is directed to assemble new viruses. Release: Enzymes disintegrate the cell in a process called lysis, releasing the new viral particles

Lytic Cycle Source: http://science.howstuffworks.com/virus-human.htm

Lysogenic Cycle The Lysogenic Cycle of a Temperate Virus: The virus attaches itself and injects its DNA into the cell. The viral DNA attaches itself to the host DNA, becoming a new set of cell genes called a prophage. When the host cell divides, this new gene is replicated and passed to new cells. This causes no harm to the cell, but may alter its traits. Now there are two possibilities: The prophage survives as a permanent part of the DNA of the host organism. Some external stimuli can cause the prophage to become active, using the cell to produce new viruses.  

Source: http://science.howstuffworks.com/virus-human.htm Lysogenic Cycle Source: http://science.howstuffworks.com/virus-human.htm

Viral Control Interferon are proteins made by cells to fight viruses Two types of viral vaccines exist --- inactivated & attenuated Inactivated virus vaccines don't replicate in the host's system Attenuated viral vaccines have been genetically altered so they can't cause disease Antiviral drugs (AZT, acyclovir, & azidothymidine) interfere with viral DNA synthesis Protease Inhibitors interfere with viral capsid production New viruses emerge as rain forests are cleared (Ebola virus)

Adenovirus Common cold Influenza Virus Note-plasma membrane

HIV Coronavirus SARS

Classification By Nucleic acids By Structure By Speed of Infection By Specificity

Classify By Nucleic Acid in Core DNA Viruses DNA inserted into host cell is incorporated into the host genome. Host cell does not differentiate Viral DNA commandeers control and signals host to replicate viral DNA and to produce viral protein. Host uses itself up to produce these Result is a hollow sack of viral particles.

Classify By Nucleic Acid in Core RNA Viruses RNA is inserted into the cell Host cell is signaled to make viral RNA and viral protein Result is the same for host cell DEATH

Polio virus is a RNA virus

Classify By Nucleic Acid in Core Retrovirus Viruses Nucleic acid is RNA but with the addition of enzyme-Reverse Transcriptase Enzyme allows production of DNA from viral RNA RNA->DNA->RNA->Protein Does this disprove the Central Dogma? Lab use of reverse transcriptase

RNA Reverse transcriptase HIV is a retrovirus

Classify By Specificity Viruses are extremely specific as to which kinds of cells they parasitize Identify protein receptors on the outside of host cells Tobacco mosaic virus does not infect animals or bacteria. The viral protein determines the specificity

Classify By Speed Lytic viruses attack the host cell quickly Lysogenic or latent viruses insert the nucleic acid and lie dormant. Unknown chemical signals activate them They may never be activated If host cell divides the viral genome is replicated along with other DNA

Mutation Viral nucleic acids can mutate Sometimes pick up parts of host DNA Sometimes pick up host membrane Three types of pathogens that have no vaccines Retroviruses Those with multiple antigens Those that mutate rapidly HIV is a retrovirus with many antigens that mutates rapidly.

Origin of Viruses Hypothesis 1. Viruses predate first cells Hypothesis 2. Viruses are cellular fragments Evidence for 2 is that some viruses wrap their DNA around histones to form nucleosomes as eukaryotic cells Viruses have followed own evolutionary path.

Viroids and Prions: The Ultimate in Simplicity Plant Viroid Prion

Viroids Naked RNA found in plant cells Infectious agents Process of infection a mystery As is replication May interfere with gene regulation

Prions Naked protein not associated with a nucleic acid Infectious agent Action unknown Identified as cause of scrapie--sheep mad cow--bovine C-J—humans

Unicellular Prokaryotes Bacteria Unicellular Prokaryotes Point of a straight pin with thousands of bacterial cells

History Leeuwenhoek Louis Pasteur Robert Petri Probably first person to see bacteria Louis Pasteur Father of bacteriology First person to study bacteria extensively Robert Petri Developed the petri dish Used to culture bacteria

Koch’s Postulates A formalized group of criteria for establishing the cause of an infectious disease The microorganism must be present in every case of a disease. The organism must be grown in pure culture from diseased hosts.

Koch’s Postulates continued The same disease must be produced when a pure culture of the organism is introduced into susceptible hosts. The organism must be recovered from the experimentally infected host.

Koch’s bacterial discovery 1876 Convincing proof of “germ theory” of disease Showed that Bacillus anthracis is cause of anthrax Often fatal disease in humans, sheep and other animals

Koch’s procedure Under microscope, observed B. anthracis cells in blood and spleen of dead sheep Inoculated mice with the infected sheep blood Recovered B. anthracis from blood of mice Grew bacteria in pure culture and showed that they caused anthrax when injected into healthy mice. From this and later work with Mycobacterium tuberculosis, Koch’s Postulates formalized

Types of Immunity Naturally acquired passive From mother at birth Temporary Recover from disease Make antibodies Permanent in most cases Artificially acquired passive From a serum Some other animal makes the antibodies Requires booster shot Example tetanus Artificially acquired active From vaccine You make the antibodies Contains dead or weakened pathogens

References http://spa.k12.ar.us/massengale/virus_notes_b1.htm