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Lecture 5 Introduction to • Important • Term • Extra explanation • Additional notes Objectives • General characteristics of viruses. • Structure & symmetry of viruses. • Classification of viruses. • Steps of replication. • Laboratory diagnosis of viral infections. REMEMBER!

Properties of Microorganisms

Characteristics Parasites Fungi Viruses

Cell Yes Yes Yes NO

Type of Nucleus Eukaryotic Eukaryotic Prokaryotic -

DNA DNA DNA DNA Nucleic Acid and RNA and RNA and RNA or RNA

Ribosomes Present Present Present Absent

Mitochondria Present Present Present Absent

Budding or Replication Mitosis Binary Fission Special Mitosis General characteristics of Viruses

Non-living, non- cellular (Acellular ) that can’t be observed by light microscope.

Obligate intracellular organism, doesn’t live outside the . Internal core of nucleic acid “DNA or RNA”.

Composed of coat surrounds the Nucleic Acid called tiny particles: “”.

Some viruses have a Replicate in a matter lipoprotein membrane of diff from cells “Envelope” 1V (virus)  many Vs (Viruses)

Don’t have like or mitochondria Structure of viruses

 The tiniest virus is only 20 nm in diameter, while the largest is several hundred nanometers – which is barley visible under the L/M.

 Some viruses could be crystallized.

 Viruses that infect bacteria are called or Phages Viral genome

Double- Single- Double- Single- stranded DNA stranded DNA stranded RNA stranded RNA (dsDNA) (ssDNA) (dsRNA) (ssRNA) o The smallest virus has only 4 while the largest has several hundreds to thousand. o All DNA Viruses have Double-stranded (ds) except Parvoviruses. o All RNA Viruses have Single-stranded (ss) except Reoviruses. o All Vs are haploid, except are diploid o DNA Always single molecule. o RNA can be (+) or (-) polarity – more on this link (http://youtu.be/ZGE4BLuAkuU) Structure of viruses based on arrangement of capsomeres

2-Capsid

Cubic symmetry Rod-shaped Helical Complex (Icosahedral).

Pleomorphic It’s a protein shell ( .) Pox Virus enclosing the viral genome. are build of a Adenovirus large Number of subunits called Capsomers Elongated (filoviruses) Function:. Herpes Genome (NA)+capsid Facilitates Protect its entry Nucleic into cell Acid nucleocapsid Structure of viruses

-During viral budding: Envelope is derived from cell membrane except herpesviruses from nuclear membrane. Enveloped viruses are more sensitive to heat, dry & other factors than nonenveloped Vs Glycoprotein attaches to host cell receptor. Viral

The outer viral proteins:

-Mediate attachment to specific receptors -Induce neutralizing -Target of antibodies

-The internal viral proteins:. -Structural( capsid proteins of enveloped viruses) -Nonstructural proteins():

*All ssRNA viruses(-) polarity have transcriptase ( RNA dependent RNA polymerase) inside virions.

*RetroViruses & HBV contain . Classification of virus Is based on:

 Chemical and physical properties of virions.  Type of Nucleic Acid (DNA or RNA)  The number of strand: Double- vs/single-stranded  The polarity of viral genome: Positive (+) or negative (-) stranded RNA  The presence or absence of envelope  Type of symmetry

Medically Important Viruses

1-DNA Single-stranded Double-stranded Nonenveloped enveloped Nonenveloped

Icosahedral Complex Icosahedral Icosahedral

Parvoviridae Adenoviridae Papovaviridae Medically Important Viruses

2-RNA

Single-stranded Double-stranded

Nonenveloped Neg-strand Pos-strand

enveloped enveloped Icosahedral Nonenveloped

Helical Helical Icosahedral Coronaviridae Paramyxoviridae Picornaviridae Hepeviridae Icosahedral Filoviridae Caliciviridae Togaviridae Bunyaviridae Astroviridae Flaviviridae Arenaviridae Retroviridae Steps of Virus Replication

• Glycoprotein (IF ENVELOPED) 1-Adsorption • Folding proteins in capsid (NON-ENVELOPED)

• Fusion: of the cell membrane and the (ONLY ENVELOPED CAN FUSE) • 2-Penetration : Virus is consumed by the endocytotic vesicle. Cell wraps around the Virus.

• Release of Viral Genome to in Direct 3-Uncoating Synthesize of Protein or to Nucleus in indirect Synthesize of protein.

• mRNA: This Step for (-) Viruses, it will use the genome to produce mRNA, and that's why it is indirect. 4-Synthesis of viral • Viral proteins: This Step for (+) RNAs, they have mRNA, it will begin components mRNA the synthesize by the Ribosomes Directly. • Replication of viral genome: The mechanism will continue for the replication, one virus will produce in one cell millions of viruses. 5-Assembly • NA + V. Proteins = Virions

• Enveloped Viruses: Viruses leaves the cell and create their Envelopes from the cell membrane OR from the nuclear mb 6-Release ex: herpes Vs. (This process is called Budding) • non-Enveloped Viruses: Cell or rupture of the cell membrane

-mRNA Viral genome mRNA +ssRNA acts directly

- Viral proteins mRNA viral proteins cell - enzymes - structural -replication of viral genome لتوضيح للخطوات السابقة laboratory diagnosis of viral infections

o Microscopic examination. o Cell culture. Electron Micrographs: o Serological tests. o Detection of viral Ag. o Molecular method.

AdenoVirus HerpesVirus

PoxVirus -Virus cultivation: Laboratory animals Embryonated eggs Cell culture 3-Cell culture

No of sub passages -Problems with cell culture: (the number of Long incubation (up to 5 days). Cell Culture illustrating Pictures times the cells have “Because one of the problems been subcultured) with cell culture is long incubation, they came up with a modified cell culture: a Rapid culture technique: Primary c/c 1 to 2 Shell vial assay (this technique detects viral in cell culture, and takes 1-3 Diploid c/c days)”. (semi continuous) 20 to 50 -Sensitivity is variable. -Susceptible to bacterial contamination. -Some viruses do not grow Continuous cell line Indefinite in cell culture e.g. HCV. Cell culture

- Detection of viral growth: Rapid culture technique Cytopathic effects. • Shell Vial Assay “Rounding, shrinkage, aggregation, and lose of adherence. • Detect viral antigens Giant Cell formation. Inclusion bodies formation: The site of • 1-3 days and protein synthesis.” -Other effects.

Molecular test: -Polymerase chain reaction (PCR) • NA amplification technique. • Viral genome. - Uses of molecular test: - • Diagnosis. - • Monitoring response to treatment. Online Quiz

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Videos

Viruses (Structure, Types and Bacteriophage Replication): https://www.youtube.com/watch?v=s8jhJXgC-bk shapes of viruses: https://www.youtube.com/watch?v=05bwTTWlIGA Classifying DNA & RNA Viruses https://www.youtube.com/watch?v=IgrsdajGes0

Books that could help you

made ridiculously simple  Sherris Medical Microbiology Girls Team • Lamya Alsaghan • Nojood Alhaidri Boys Team • Monera Alayuni • Ali Alzahrani • Alanoud AlOmair • Khalid Sharahily • Shahad Alenezi • Ahmad Alzahrani • Aisha Al-Sabbagh • Zeyad Alsalem • Bodour Julaidan • Muhammad Dossary • Noura AlTawil • Meshal Alhazmy • Deema AlFaris • Hamzah Alfiar • Sara Al-Hussein • Suha Alenezy • Latifah Alsukait [email protected] • Dalal Alhuzaimi • Reema Allhaidan @microbiology435 Contact us! http://ask.fm/microbiology435

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