virus_study_more_aboit_viruses_pptx.pptx

Viruses details

1. Viruses – Discovery, general structure, replication, DNA virus (T phage); Lytic and lysogenic cycle, RNA virus (TMV) and Economic importance

2. Viruses are sub microscopic non cellular particles made up of genetic material and protein Require another cell to survive Viruses are “ biological entities ” containing either DNA or RNA . Introduction

3. Virology - study of viruses First vaccine against virus -Small Pox vaccine (1796) by Edward Jenner Cowpox virus ( vaccinia virus) conferred immunity against deadly smallpox ( Variola virus) Louis Pasteur – Rabies vaccine (1885)

4. Discovery of Virus Adolf Mayer  first described the tobacco mosaic disease (1886) that could be transferred between plants, similar to  bacterial  infections Dmitri Ivanovsky in 1892 used one of Chamberland filter  (1884) to show that sap froma diseased  tobacco plant  remained infectious to healthy tobacco plants despite having been filtered. 

5. Dmitri Ivanovsky - Contagium vivum fluidum (Filterable Pathogen) Martinus Beijerinck called the filtered, infectious substance a "virus” Tobacco Mosaic Virus (TMV)

6. in 1917 by the French Canadian scientist  Félix H. d’Hérelle , in  cultures of bacteria were discovered an agent called  bacteriophage  (“eater of bacteria”) In independent studies in 1915 by the British investigator  Frederick W. Twort   and

7. General characterstics of viruses Absence of cellular structure O bligate intracellular parasite Each viral particle, outside the host exist in the form of independent particle called Virion   Virion , consists of a single nucleic acid, RNA or DNA, surrounded by a protein coat, and is capable of replication only within the living host

8. Viruses occupy a special taxonomic position: they are not plants, animals, or  prokaryotic  bacteria viruses should not even be considered organisms, in the strictest sense, because they are not free-living—i.e., they cannot reproduce and carry on metabolic processes without a host  cell .

9. T hey depend on the host cell for almost all of their life-sustaining functions. Unlike true organisms, viruses cannot synthesize proteins, because they lack  ribosomes  (cell organelles) for the translation of viral  messenger RNA  

10. Viruses are also energy parasites; unlike cells, they cannot generate or store energy in the form of  adenosine triphosphate  (ATP). Absence of respiration The virus derives energy, as well as all other metabolic functions, from the host cell.

11. Require Trasmission The true infectious part of any virus is its nucleic acid, either DNA or RNA but never both Viruses do not divide in chemically defined media Mutation- they undergo heritable mutations

12. Structure:  Envelop: Some viruses have a  phospholipid envelope , derived from the infected host’s cell membrane, that surrounds the protein capsid .

13. Envelop have usually viral encoded proteins know as  spike projections  – these are typically glycoproteins and are also involved in receptor recognition and viral tropism. A classical example of this is the  neuraminidase  and  haemagglutinin   glycoproteins expressed on the surface of the influenza A virus.

14. Influenza A virus is the only   species  of the   genus   Alphainfluenzavirus  of the virus family   Orthomyxoviridae .  It is an   RNA virus   categorized into subtypes based on the type of two   proteins   on the surface of the viral envelope : H =  hemagglutinin , a protein that causes  red blood cells   to   agglutinate . N =  neuraminidase , an enzyme that cleaves the   glycosidic bonds  of the   monosaccharide   sialic acid  ( previously called   neuraminic acid )

15. Capsid A typical virus consists of a protective protein coat, known as a  capsid . Shape : Helical (TMV, Mumps virus, rabies virus), Cubical [spherical (influenza virus) and polyhedral ( herps virus)], icosahedral (Polio virus) forms to more complex Binalsymmetry ( Bacteriophages , T2, T4, cyanophages , pox ( vaccina ) virus) with tails.

16. Capsid has three functions: Protection - protect the viral nucleic acid from digestion by certain enzymes ( nucleases ) ( 2)Receptor recognition - sites on its surface recognize and attaches the virion to  receptors  on the surface of the host cell

17. (3)Targeting the virus to a susceptible host - enables the virion to penetrate through the cell surface membrane or, in special cases, to inject the infectious nucleic acid into the interior of the host cell.

18. Nucleic acid Either DNA or RNA but never both

19. Replication T here are six basic stages that are essential for viral replication. 1. Attachment: Viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cellular surface. This specificity determines the host range ( tropism ) of a virus

20. 2. Penetration : The process of attachment to a specific receptor can induce conformational changes in viral capsid proteins, or the lipid envelope, that results in the fusion of viral and cellular membranes 3. Uncoating : The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid

21. 4. Replication: After the viral genome has been uncoated, transcription or translation of the viral genome is initiated. This process culminates in the de novo synthesis of viral proteins and genome.

22. 5. Assembly: Viral proteins are packaged with newly replicated viral genome into new virions that are ready for release from the host cell. This process can also be referred to as maturation.

23. Virion release: There are two methods of viral release: lysis or budding Lysis results in the death of an infected host cell, these types of viruses are referred to as cytolytic . An example is variola major also known as smallpox.

24. Budding Enveloped viruses, such as influenza A virus, are typically released from the host cell by budding. It is this process that results in the acquisition of the viral phospholipid envelope. These types of virus do not usually kill the infected cell and are termed cytopathic viruses .

25. T phase

26. Genome Double stranded DNA (169KBP) 160 genes Encodes 289 proteins

27. T4 initiates infection by binding OmpC porin proteins and lipopolysaccharides (LPS) On the surface of E.coli with its long tail fibers (LTF) Recognition signal is sent through LTF to base plate Base plate unravels the short tail fiber that bind irreversibly to E. coli Base plate changes conformation and tail sheath contracts causing tail tube to puncture the membrane

28. Lytic and Lysogenic cycle

29. TMV Virus First virus that was crystallized in 1935 by WM stanley in USA Rod-like and Inside protein capsid there is single stranded RNA

30. Capsid  is made from 2130 molecules of coat protein RNA having 6500 nucleotide 49 nucleotide ,16.3 proteins per helix turn

31. The protein monomer consists of 158  amino acids  which are assembled into four main alpha-helices. Virions are ~300 nm in length and ~18 nm in diameter

32. Economic importance Harmful Effects of Viruses human and animal diseases. Viruses are epidemic which spreads rapidly to many people (Small pox) Viruses are pandemic which spread diseases worldwide. COVID-19 is very life threatening disease that already has taken the lives of nearly few lakhs people worldwide.

33. In 2003, the severe acute respiratory syndrome (SARS) also took the lives of nearly 800 people worldwide. Viruses can cause devastating epidemics in human societies. They can be weaponised for biological warfare.

34. Viruses Name of diseases Host Influenza virus Influenza Herpes virus Herpes Hepatitis A, B, C, D, & E virus Jaundice HIV AIDS Variola virus Small pox Rubeola virus Measles Polio virus Polio Rabies virus Rabies Yellow fever virus Yellow fever Flavi virus Dengue Vaccinia virus Cow pox

35. Foot and mouth virus Foot and mouth disease Papaya ring spot virus Papaya ring spot disease Tobacco mosaic virus Tobacco mosaic disease Bean mosaic virus Bean mosaic disease Tungro virus Tungro disease of rice Bushy stunt virus Bushy stunt disease of tomato Bunchy top virus Bunchy top disease of banana

36. A vast number of viruses cause plant diseases as Rice tungro baciliform virus (RTBV), Tobacco mosaic virus (TMV), Tomato/papaya ring spot virus, Tomato leaf curl, Potato leaf roll virus, etc.

37. Beneficial Effect of Viruses There are many industrial uses of viruses. Viruses are used in preparation of  sera  and vaccines to be used against diseases like rabeis , polio, hepatitis B, pox, mumps, etc.

38. The multiplication of viruses in bactereial cells is also utilized in the production of antibodies. Viruses are also used in biological studies to understand the basic mechanisms of molecular genetics.

39. It is used in genetic engineering as vectors or carriers that take the required material for treatment of a disease to various target cells .

40. Virotherapy uses viruses as vectors to treat various diseases, as they can specifically target cells and DNA. It shows promising use in the treatment of cancer and in gene therapy, to cure genetic disorder ( eg Cystic fibrosis).

41. Viruses are used in biological control by human in eradicating pests like insects (by NPV) and in controlling the population of organisms such as rabbits by inducing viral infection.

42. Viruses play an important role in regulating the freshwater and saltwater ecosystem by destroying bacteria and recycling carbon in the aquatic  ecosystem . Bacteriophage can be used in water preservation as it can destroy the bacteria and keep water fresh.