Medical Microbiology Virology PDF

Medical Microbiology Virology Dr. Aymen Samir Yassin [email protected]  Virology Introduction DNA viruses RNA viruses Hepatitis  Virology Introduction DNA viruses RNA viruses Hepatitis Introduction (for all viruses) General properties Stru...

Medical Microbiology Virology Dr. Aymen Samir Yassin [email protected]  Virology Introduction DNA viruses RNA viruses Hepatitis  Virology Introduction DNA viruses RNA viruses Hepatitis Introduction (for all viruses) General properties Structure Life cycle Cultivation Infection Diagnosis Treatment  Viruses … Many infections of humans, animals, and plants are caused by (noncellular) agents: viruses. Viruses cause many of the diseases that are very common around the world: the common cold, influenza, and AIDS, to name a few. And now Corona, Ebola, ZIKA, and Dengue…  General characteristics of viruses ❖ They are simple compared to a cell—lacking cell membranes. ❖ Composed of only a few organic molecules. ❖ They lack most of the characteristics of life. ❖ Viruses cannot carry out any metabolic pathway. ❖ They can neither grow nor respond to the environment. ❖ They cannot reproduce independently. ❖ They must utilize the chemical and structural components of the cells they infect to produce more molecules of viral nucleic acids and viral proteins which assemble into new viruses in order to increase their numbers. ❖ Acellular, no cytoplasmic membrane, cytosol or functional organelles. ❖ Outside the cell, known as virion (the infectious form of the virus).  General characteristics of viruses Composition of a virus Capsid - A virion consists of a protein coat, called a capsid, surrounding a nucleic acid core. - The capsid of a virus is composed of proteinaceous subunits called capsomeres. - Some capsomeres are composed of only a single type of protein, whereas others are composed of several different kinds of proteins. Nucleic acids - The genome of a virus may be either DNA or RNA, single stranded or double stranded. - The genome of any particular virus may be either linear or composed of several molecules of nucleic acids or circular and single. Envelop (not in all viruses) - Some virions have a phospholipid membrane called an envelope surrounding the nucleocapsid (Nucleic acid + capsid). Hosts of viruses ❖ Most viruses infect only a particular host’s cells. ❖ This specificity is due to the precise affinity of viral surface proteins or glycoproteins (ligands or spikes) for complementary proteins or glycoproteins on the surface of the host cell (receptors). ❖ Viruses may be so specific that they infect not only a particular host but also a particular kind of cell in that host. ❖ All types of organisms are susceptible to some sort of viral attack (plants, bacteria, fungi, protozoa, insects, animals). Sizes of viruses ❖ Viruses are so small that only a few can be seen by light microscopy. ❖ Smaller viruses have a diameter of 24 nm (10-9 m); and the largest virus is about 500 nm in diameter, which is about the diameter of many bacterial cells. Shapes of viruses There are three basic types of viral shapes: helical, polyhedral (icosahedral (20 faces)), and complex. The viral envelop - A virus with a membrane is an enveloped virion, a virion without an envelope is called a nonenveloped or naked virion. - An enveloped virus acquires its envelope from its host cell. - Other viral proteins called matrix proteins fill the region between capsid and envelope. - A viral envelope is composed of a phospholipid bilayer and proteins.(Similar to cell membrane composition NOT function). - Some of the proteins are virally coded glycoproteins, which appear as spikes protruding outward from the envelope’s surface. - An envelope’s proteins and glycoproteins often play a role in the recognition of host cells. Classification of viruses ❖ By their type of nucleic acid, presence of an envelope, shape, and size. So far, they have established families for all viral genera. ❖ Family names are typically derived either from special characteristics of viruses within the family or from the name of an important member of the family. ❖ Picornaviridae contains very small RNA viruses, and Hepadnaviridae contains a DNA virus that causes hepatitis B.  Viruses Cells Inert macromolecules outside of a cell but Metabolize on their own become active inside a cell Do not divide or grow Divide and grow Acellular Cellular Obligate intracellular parasites Most are free living Genetic material either DNA or RNA Genetic material DNA Genome can be dsDNA, ssDNA, dsRNA, Genome is dsDNA or ssRNA Usually ultramicroscopic in size, ranging from 200 nm to 12 cm in diameter 10 nm to 500 nm Have a proteinaceous capsid around Surrounded by a phospholipid membrane genome; some have an envelope around the and often a cell wall capsid Replicate in an assembly-line manner using Self-replicating by asexual and/or sexual the enzymes and organelles of a host cell means