Introduction to Virology

Introduction to Virology. Shah Faisal Jamal KMU-IPMS.

Contents. History Major Virology Milestones Introduction Virus Structure Size and Shapes Atypical Virus Like agent Classification.

History. Although Louis Pasteur and Edward Jenner developed the first vaccines to protect against viral infections Edward Jenner (1798), introduced the term virus in microbiology. Edward Jenner noticed that milk maids who infected with cowpox develop immunity against smallpox. He inoculated a boy with the vesicle fluid taken from the hand of infected maid. The boy developed sustained immunity against smallpox..

[Audio] Chamber Land- filter paper having pores smaller than bacteria..

Major Virology Milestones. [image] .2 by of R aga Growth Of poliovirus Bacteriophage a ly is by gene u C e ng. splicing Virology 1798 1885 1802 1000 1911 191 s 1917 193 s 1952 1957 1 oss 1968 197 1 19709 1976 1977 107 s—1090 Sei e Paul Fro Finlay Peyto Felix Max Theiler John vv•ener Hershey Alick Jonas Renato Gaia Michael Bishop d I-larola V Phillip Sh 19S1 069 10 196 s 1969 197 s 1976 1076 197 s 1 007.

Introduction. Viruses are obligate intracellular parasites i-e they replicate only inside living cells. Viruses are not cells; they are not capable of independent replication, can synthesize neither their own energy nor their own proteins, and are too small to be seen in the light microscope Viruses contain only one type of nucleic acid, either DNA or RNA, but never both. Viruses consist of nucleic acid surrounded by a protein coat. Viruses do not have a nucleus, cytoplasm, mitochondria or ribosomes..

Introduction. Viruses must reproduce (replicate) within cells, because they cannot generate energy or synthesize proteins. Viruses do not multiply in chemically defined media. Viruses do not undergo binary fission or mitosis. One virus can replicate to produce hundreds of progeny virus. Virus particles can only be observed by an electron microscope.

[Audio] icosahedral. Virus Structure. All viruses have a protein coat called a capsid that covers the genome composed of repeating subunits called capsomers. In some viruses the capsid is covered with a lipoprotein envelope. Nucleic acid plus the capsid is called the nucleocapsid. The repeating subunits of the capsid give the virus a symmetric appearance. Some viral nucleocapsids have spherical (icosahedral) symmetry, whereas others have helical symmetry. All human viruses that have a helical nucleocapsid are enveloped (i.e., there are no naked helical viruses that infect humans). Viruses that have an icosahedral nucleocapsid can be either enveloped or naked..

[image] Envelope protein Envelope Viral genome nucleocapsid Viral tegument.

[Audio] Arenaviruses have a few nonfunctional ribosomes.

Size and shape of viruses. Viruses are smaller than bacteria, they range in size between 20 nm (mouth and foot virus) to 300 nm (Poxviridae) Their shapes are frequently referred to in colloquial terms (e.g., spheres, rods, bullets, or bricks) But in reality they are complex structures of precise geometric symmetry. The shape of virus particles is determined by the arrangement of the repeating subunits that form the protein coat (capsid) of the virus..

[Audio] NMR- nuclear Magnetic Resonance. Size of virus.

[image] (Luu OOE x Luu s l) snJ!A oneqox (wu OOE x Luu OOZ) snu!,•, xodllews OOE (Luu VZ) ZSIA' a6eqdowape8 (Luu S ZZ x Luu 05) VI 5eqdowape8 Luu OSL sawosoq!J (wu OE) oosz (mewe!p u! wu OOO'OL) poolq pay (Luu OOOE x wu 0001) (wnæaDeq) •3.

[image] Potyhedr•l Helical Vitus) Spherical.

What are the challenges the way we define life?.

Atypical virus like agents. Defective viruses are composed of viral nucleic acid and proteins but cannot replicate without a “helper” virus Pseudovirions contain host cell DNA instead of viral DNA within the capsid. Viroids consist solely of a single molecule of circular RNA without a protein coat or envelope. Prions are infectious particles that are composed solely of protein (i.e., they contain no detectable nucleic acid)..

[image] VIRUS VIRUS An infective agent that typically consists of a nucleic acid molecule in a protein coat and is able to multiply only within the living cells of a host A very simple particle that can infect other living cells Made up of a nucleic acid molecule covered by a protein coat Can cause a wide variety of infections PRION PRION An infectious protein particle similar to a virus but lacking nucleic acid; thought to be the agent responsible for scrapie and other degenerative diseases of the nervous system Less complex even than a virus Made up of only proteins Mainly cause neuro- degenerative diseases Visit www.PEDIAA.com.

[Audio] Realm - a primary biogeographical division of the earth's surface.

Baltimore Virus Classification. Baltimore classification (first defined in 1971) is a classification system that places viruses into one of seven groups depending on a combination of their nucleic acid (DNA or RNA), strandedness (single-stranded or double-stranded), Sense, and method of replication. Named after David Baltimore, a Nobel Prize-winning biologist, these groups are designated by Roman numerals..

[Audio] Positive-sense Negative-antisense-template.

[image] dsDNA viruses Poxvilidae Asfavilidae Ilidovilidae Herpesvilidae Adenoviridae Polyomavilidae Papillomavitidae ssDNA viruses Circovilidae Anellovirus Patvovilidae dsRNA viruses Reovilidae Birnavihdae ssRNA (+) viruses Picornavilidae Calicivihdae Hepevirus Astrovilidae Nodavilidae Coronavihdae Altewitidae Flavivilidae Togavilidae ERNA G) viruses Bornavilidae Rhabdovilidae Filovilidae Paramyxovilidae Olthomyxovilidae Bunyavilidae Arenavilidae Deltavirus RNA and DNA (RT) viruses Retrovilidae (RNA) Hepadnavi\idae (DNA).

DNA Viruses. Sometimes referred to as the HHAPPPy viruses: Herpes Hepadna Adeno Papova Parvo Pox Most DNA viruses are double-stranded, show icosahedral symmetry, and replicate in the nucleus.

DNA Viruses. Two DNA viruses break these rules: Parvoviridae: This virus is so simple that it only has a single strand of DNA 2) Poxviridae: This virus is at the opposite end of the spectrum and is extremely complex. Although it does have double-stranded DNA, the DNA is complex in nature, coding for hundreds of proteins. This virus does not have icosahedral symmetry. The DNA is surrounded by complex structural proteins looking much like a box ( POX IN A BOX). This virus replicates in the cytoplasm.

DNA Viruses. Three of the DNA viruses have envelopes: Herpes Hepadna Pox Three are naked: Papova Adeno Parvo.

[image] DNAVIRUSES ENVELOPED Double•Stranded NAKED Double•Stranded Icosohedral PAPOVA ADENO Single•Stranded Icosohedral Icosohedral HERPES HEPADNA Complex (Pox in a box).

RNA viruses. There are certain generalities about RNA viruses, most of which are the opposite of DNA viruses. Most RNA viruses are single-stranded (half are positive [+1 stranded, half negative -1), enveloped, show helical capsid symmetry RNA viruses replicate in the cytoplasm.

RNA Viruses. Toga Corona Retro Picorna Calici Reo Orthomyxo Paramyxo Rhabdo Bunya Arena Fibo.

RNA Viruses. Exceptions: 1) Reoviridae are double-stranded 2) Three are non-enveloped: Picorna, Calici, and Reoviridae 3) Five have icosahedral symmetry: Reo, Picorna,Toga, Flavi, Calici (Rhabdo has helical symmetry but shaped like a bullet). 4) Two undergo replication in the nucleus: Retro, Orthomyxo.

[image] Single- Positive-Stranded RNA VIRUSES tranded Negative-Stranded Doubl -Stranded Naked *PICORN •CALICI *Icosohedral; Enveloped •TOGA •FLAVI CORONA RETRO Enveloped BUNYA ORTHOMYX PARAMYXO Naked *REO shaped) All of the rest RHABDO ARENA FILO have helical (Bullet symmetry.

Thank You.