viruses lecture.pptx

8/14/2019 VIRUSES LECTURE.pptx

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VIRUSESIRUSES


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Smallest to largest..Prions

Viruses

BacteriaFungi


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PrionsInfectious proteinNo DNA or RNANormal cellular form of protein vs.pathological form

Pathological form

found in neuraltissue and tonsils

PrP-C & PrP-Sc


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PathologySpongiform

encephalopathy:transmissible,familial

Transmission: oral,operative (neuraltissue, dura,corneas), ???

bloodResistance to

disinfectantsFormaldehyde

increases

infectivity


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VirusesNon-cellular

No cellular composition

Do not grow or metabolize organic materials

Produce no waste products

Do not utilize energy

Do not adapt to their environment

Reproduce only within living cells (cannotreproduce on their own)

Size range from 20 nm (polio virus) to 300 nm(pox virus)


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Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell


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Viral ShapesIcosahedral I.M., mumps, chicken pox and

herpes simplex

Helical rabies and tobacco mosaic virus

Box shape coxpox and small pox


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Figure 18.2 Viral structure


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The Structure Of a Virus

Viruses arecomposed of acore of nucleic

acidThe Nucleic acid

core is surroundedby a protein coat

called a capsidThe Nucleic core is

either made up ofDNA or RNA butnever both


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Viruses

Composed of genome in a capsidDNA or RNA

Shell of protein (capsid) surrounding nucleicacid

Capsid is composed of repeating units of

capsomeres (proteins)

Envelope, spike

Classification on basis of nucleic acid

DNA viruses: eg Herpes simplexvirus (HSV)

RNA viruses: eg influenza virus


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DNA viruses: herpes simplex virus (HSV)


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RNA viruses: Influenza


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CapsidCapsidFunctions

Protection of NAAttachment for

naked viruses

Enzyme


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EnvelopeEnvelope

AttachmentEntry

Assembly- matrixproteins

ReleaseProteins are viral

Lipids are host If the membrane envelope is

destroyed, the virus becomesnoninfectious. Why?


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Bacteriophages attack

bacteria (prokaryotes)viruses attack eukaryotic

cells.

Viruses and bacteriophages invade

cells and use the host cell'smachinery to synthesize more oftheir own macromolecules.

Once inside the host the

bacteriophage or virus will eithergo into a Lytic Cycle-

destroying the host cellduring reproduction.

or

It will go into a Lysogenic Cycle- a


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Viral effects on host cells

Degeneration (cytopathic effect): CMV

Cell lysis

Cell fusion, syncytia formation: RSV

Cell proliferation

Transformation: malignancy (parvoviruses)

Latent infection - no sign of infection until

reactivation

cold sores (HSV) chickenpox shingles (VZV)


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Mode of Attack

DNA to mRNA to Ribosomes tomake new viruses

RNA to Ribosomes to make new

viruses

Result the cell dies


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HIV is a retrovirus injecting the enzyme, reversetranscriptase into the cell to copy viral RNA intoDNA.


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iru se s a re h o st sp e cific a p ro te in o n th e su rfa ce o f th e v ir

a s a sh a p e th a t m a tch e s a m o le cu le in th e p la sm a m e m b ra

, .f its h o st a llo w in g th e viru s to lo ck o n to th e h o st ce ll


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HIV doesnt target just any cell, it goes right for thecells that want to kill it. Helper" T cells are HIV'sprimary target. These cells help direct the immune

system's response to various pathogens.


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PathwaysLytic = RNA or DNA routes

Lysogenic = RNA to DNA to

mRNA to Ribosomes A

reverse route through thecell.


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Figure 18.3 A simplifiedviral reproductive cycle

Figure 18.6 The reproductive cycle of an enveloped virus


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Figure 18.6 The reproductive cycle of an enveloped virus

Figure 18.4 The lytic cycle of phage T4


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Figure 18.4 The lytic cycle of phage T4

Figure 18.5 The lysogenic and lytic reproductive cycles of phage , a temperate phage


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gu e 8 5 e ysoge c a d y c ep oduc e cyc es o p age , a e pe a e p age


28/34The Lytic Cycle


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VaccinesViruses grown on chicken embryos areattenuated vaccines

Another type of vaccine is made by heatkilling the virus


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CMV hepatitis

owl eye effect inclusion body


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Varicella zoster virus (VZV)

VZV: Chickenpox

VZV: Shingles

Re-activation oflatent infection

Suppression of

cell mediatedimmunity


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Strategy ofreplication

Lytic

Temperate

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