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VIRAL HISTORY copyright cmassengale 1 • Discovery of Viruses • . In 1892 Russian Biologist Iwanowsky showed that disease was due to something smaller than bacteria. • Mayer in 1886 mention about disease was tobacco mosaic disease copyright cmassengale 2 •Beijerinck (1897) coined the Latin name “virus” meaning poison •He studied filtered plant juices & found they caused healthy plants to become sick copyright cmassengale 3 Tobacco Mosaic Virus •Wendell Stanley (1935) crystallized sap from sick tobacco plants •He discovered viruses were made of nucleic acid and protein copyright cmassengale 4 Smallpox •Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses •Deadly viruses are said to be virulent •Smallpox has been eradicated in the world today copyright cmassengale 5 Viewing Viruses •Viruses are smaller than the smallest cell •Measured in nanometers •Viruses couldn’t be seen until the electron microscope was invented in the 20th century copyright cmassengale 6 Size of Viruses copyright cmassengale 7 Characteristics • Non living structures • Non-cellular • Contain a protein coat called the capsid • Have a nucleic acid core containing DNA or RNA • Capable of reproducing only when inside a HOST cell copyright cmassengale 8 Characteristics •Viral capsids (coats) are made of individual protein subunits •Individual subunits are called capsomeres copyright cmassengale CAPSOMERES 9 Characteristics •Outside of host cells, viruses are inactive •Lack ribosomes and enzymes needed for metabolism •Use the raw materials and enzymes of the host cell to be able to reproduce EBOLA VIRUS HIV VIRUS copyright cmassengale 10 Viral Shapes •Viruses come in a variety of shapes •Some may be helical shape like the Ebola virus •Some may be polyhedral shapes like the influenza virus •Others have more complex shapes like bacteriophages copyright cmassengale 11 Helical Viruses copyright cmassengale 12 Polyhedral Viruses copyright cmassengale 13 Complex Viruses copyright cmassengale 14 Structure of viruses • Viruses consist of Nucleic acid, Capsids ,Viral Envelope and tail fiber. • Their nucleic acid may consists of a single or several molecules of DNA or RNA. The smallest viruses have four genes while the largest have up to two hundreds. • Capsid : The protein coat that encloses the nucleic acid is called a capsid. It may be are different shapes. • Capsid is made up of protein subunits called capsomeres • The number of capsomers is characteristics of a particular virus. copyright cmassengale 15 • Viral envelopes: These are membranous covering around the capsid. • It is found some viruses. • This covering helps them to infect their hosts. • Tail fibers: In bacteriophage virus lower part is tail like. At the posterior end of tail some fiber like structures are present called tail fiber. • These fibers take part in the attachment of virus with host cell. copyright cmassengale 16 Adenovirus COMMON COLD copyright cmassengale 17 Influenza Virus copyright cmassengale 18 Chickenpox Virus copyright cmassengale 19 Used for Virus Identification • • • • RNA or DNA Virus Do or do NOT have an envelope Capsid shape HOST they infect copyright cmassengale 20 Bacteriophages copyright cmassengale 21 Phages •Viruses that attack bacteria are called bacteriophage or just phage •T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails copyright cmassengale 22 Bacteriophage Replication •Bacteriophage inject their nucleic acid •They lyse (break open) the bacterial cell when replication is finished copyright cmassengale 23 Lytic Cycle Review • Attachment • Penetration • Biosynthesis • Maturation • Release Phage attaches by tail fibers to host cell Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell Production of phage DNA and proteins Assembly of phage particles Phage lysozyme breaks cell wall copyright cmassengale 24 Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath 1 Tail fiber Attachment: Phage attaches to host cell. Tail Base plate Pin Cell wall Plasma membrane 2 Penetration: Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core 3 Merozoites released into bloodsteam from liver may infect new red blood cells copyright cmassengale 25 Tail DNA 4 5 Maturation: Viral components are assembled into virions. Capsid Release: Host cell lyses and new virions are released. Tail fibers copyright cmassengale 26 Viral Latency •Once a prophage cell is activated, host cell enters the lytic cell •New viruses form a & the cell lyses (bursts) •Virus said to be virulent (deadly) ACTIVE STAGE INACTIVE STAGE copyright cmassengale 27 Virulent Viruses HOST CELL LYSES & DIES copyright cmassengale 28 The Lysogenic Cycle copyright cmassengale 29 Virulence VIRUS DESTROYING HOST CELL copyright cmassengale 30 Treatment for Viral Disease copyright cmassengale 31 Vaccines • An attenuated virus is a weakened, less vigorous virus • “Attenuate" refers to procedures that weaken an agent of disease (heating) • A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus • Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness copyright cmassengale 32 Other Viral Treatments •Interferon are naturally occurring proteins made by cells to fight viruses •Genetic altering of viruses (attenuated viruses) •Antiviral drugs (AZT) •Protease inhibitors – prevent capsid formation copyright cmassengale 33 copyright cmassengale 34