Presentation 0n virus (09 12-2014)
- 2. PRESENTED BY ..... Asraful Islam Rayhan R0ll- 131039 DEPT. OF PHARMACY JESSORE UNIVERSITY OF SCIENCE & TECHNOLOGY
- 3. Outline…………. Definition of virus General properties of virus Size Structure Classification Morphology and Multiplication 0f viruses
- 4. A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from Animals and plants to bacteria and archaea. Example-Harpies virus
- 5. Properties Of virus Viruses are inert (nucleoprotein ) filterable Agents Viruses are obligate intracellular parasites Viruses cannot make energy or proteins independent of a host cell Viral genome are RNA or DNA but not both. Viruses have a naked capsid or envelope with attached proteins Viruses do not have the genetic capability to multiply by division. Viruses are non-living entities
- 6. Consequences of Virus Properties Viruses are not living Viruses must be infectious to endure in nature Viruses must be able to use host cell processes to produce their components (viral messenger RNA, protein, and identical copies of the genome) Viruses must encode any required processes not provided by the cell Viral components must self-assemble
- 7. Size of Viruses A small virus has a diameter of about 20nm. Example- parvovirus A large virus have a diameter of up to 400nm Example- poxvirus
- 8. Structure of Viruses Virions are complete, fully developed viral particles composed of nucleic acid surrounded by a protein coat. Some viruses have an envelope composed of a phospholipid bilayer with viral glycoproteins. It contain- nucleic acid, Capsid , Envelope…
- 10. 1. Nucleic acid…… Viral genomes are either DNA or RNA (not both). Nucleic acid may be single- or double-stranded Nucleic acid may be circular or linear or separate molecules. Nucleic acid protein ranges from about 1% - 50%.
- 11. 2. Capsid…… The protein shell, or coat, that encloses the nucleic acid genome. Functions: a. Protect the viral nucleic acid. b. Participate in the viral infection. c. Share the antigenicity
- 12. 3.Envelope… * The outer covering of some viruses. *The envelope is derived from the host cell plasma membrane when the virus buds out.
- 14. Virus are mainly classified by phenotypic characteristics , such as – Morphology, nucleic acid type , mode of replication , Host organisms and the type of disease the cause. Two main methods are used for the classification of viruses - 1. ICTV ( International Committee On Taxonomy of Viruses ). 2. Baltimore.
- 16. Baltimore Classification System Viruses are classed into 7 types of genes…… Class 1: Double Stranded DNA Viruses Class 2: Single-stranded DNA viruses Class 3: Double-stranded RNA viruses Class 4: Single-stranded RNA viruses - Positive-sense Class 5: Single-stranded RNA viruses - Negative-sense Class 6: Positive-sense single-stranded RNA viruses that replicate through a DNA intermediate Class 7: Double-stranded DNA viruses that replicate through a single-stranded RNA intermediate
- 17. On the basis of nucleic acid , virus are two types- Virus DNA virus Example-papiloma virus RNA virus Example-Rhinovirus
- 18. Classification on the basis of host VIRUS Human Virus Ex-smallpox 0ther virus ( Birds virus) Ex-hog cholera Fish virus Ex-carp pox Plant Ex-TMV Bacteriophage Ex-T2 virus
- 19. Morphology…. Viruses may be classified into several different morphological types on the basis of their capsid architecture. The structure of these capsids has been revealed by electron microscopy and a technique called X-ray crystallography.
- 20. 1.Helical Viruses Helical viruses resemble long rods that may be rigid or flexible. The viral nucleic acid is found within a hollow, cylindrical capsid that has a helical structure . Example-Rabis virus
- 21. Fig- Rabis virus
- 22. 2. Polyhedral Viruses Many animal, plant, and bacterial viruses are polyhedral. The capsid of most polyhedral virus of an icosahedron, a regular polyhedron with 20 triangular faces and 12 corners is in the shape. Example- Adenovirus
- 24. 3. Enveloped Viruses The capsid of some viruses is covered by an envelope. Enveloped viruses are roughly sphericaL . When helical or polyhedral viruses are enclosed by envelopes, they are called enveloped helical or enveloped polyhedral viruses. Example- Influenza virus
- 25. Fig – Influenza virus
- 26. 4. Complex Viruses Some viruses, particularly bacterial viruses, have complicated structures and are called complex viruses. the capsid (head) is polyhedral and that the tail sheath is helicaL The head contains the nucleic acid. Example- variola virus
- 27. Fig- Variola virus
- 29. Viral Multiplication For a virus multiplication it must induce a living host to synthesize all the essential components needed to make more virus. The components must then be assembled into new virions that escape from the cell. The phases of viral multiplication can be divided into five steps
- 30. The five steps of multiplication given below 1. Attachdment (adsorption) of the virion to susceptible host cell. 2. Penetration (entry , injection ) of the virion or its nucleic acid into the cell. 3. Synthesis of virus nucleic acid and protein by cell metabolism as redirected by the virus.
- 31. 4. Assembly of capsids and packaging of viral genomes Into new virions. This whole process is called maturation. 5. Release of mature virion from the cell.
- 32. Fig – the multiplication cycle of a virus
- 33. Growth curve of virus
- 34. Descriptions of growth curve Following adsorption, the infectivity of the virus particles disappears, a phenomenon called eclipse. This is due to the uncoating of the virus particles. During the latent period, replication of viral nucleic acid and protein occurs. The maturation period follows, when virus nucleic acid and protein are assembled into mature virus particles. At this time, if the cells are broken open, active virus can be detected. Finally, release occurs, either with or without cell lysis. The timing of the one-step growth cycle varies with the virus and host. 20-60min in many bacterial viruses. 8-40h in most animal hosts