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Chapter 10 Viruses Viruses contain DNA or RNA

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Presentation on theme: "Chapter 10 Viruses Viruses contain DNA or RNA"— Presentation transcript:

1 Chapter 10 Viruses Viruses contain DNA or RNA
And a protein coat called a The capsid is composed of individual Some are enclosed by an envelope May have spikes protruding from envelope

2 Most viruses infect only specific types of cells in one host
Host range is determined by specific host attachment sites and cellular factors

3 Viruses

4 Polyhedral Viruses

5 Helical Viruses Causes systemic infection often with hemorrhagic fever

6 Complex Viruses

7 Viral Taxonomy Family names end in -viridae Genus names end in -virus
A group of viruses sharing the same genes and host. Common names are used for species Subspecies are designated by a number

8 Viral Taxonomy Family : Herpesviridae Genus: Simplexvirus
Species/Subspecies: Human herpes virus 1, HHV 2 Family: Retroviridae Genus: Lentivirus Species/Subspecies: Human Immunodeficiency Virus 1, HIV 2

9 Growing Animal Viruses
Animal viruses may be grown in living animals In embryonated eggs or in cell culture.

10 Growing Viruses Animal (and plant) viruses may be grown in cell culture. For research purposes For clinical identification of virus type By observing

11 Virus Identification Some cytopathic effects (not comfirmatory)
Inclusion bodies - rabies virus Syncytia formation – measles, common cold Transformation – human papillomavirus

12 Virus Identification Serological tests
Detect antibodies against viruses in a patient Use antibodies to identify viruses Western blot Viral nucleic acids: RFLPs (i.e. DNA Fingerprinting), PCR tests

13 Virus Identification – a cytopathic effect

14 Viral Multiplication Viruses require host cell “machinery” for replication Some viruses have some of their own enzymes: mainly for viral nucleic acid replication Most, if not all, enzymes come from host cell These enzymes are involved in building new virions

15 Multiplication of Bacteriophages (Lytic Cycle)
Phage causes lysis and death of host cell Attachment Phage attaches by tail fibers to host cell Penetration Phage lysozyme opens cell wall; DNA is then “injected” into cell Biosynthesis Production of phage DNA and proteins Maturation Assembly of phage particles Release Phage lysozyme breaks cell wall

16 1 2 3 Bacterial cell wall Bacterial chromosome Capsid DNA Capsid
Sheath Tail fiber 1 Attachment: Phage attaches to host cell. Tail Base plate Pin Cell wall Plasma membrane 2 Penetration: Phage penetrates host cell and injects its DNA. Sheath contracted Tail core 3 Biosynthesis: phage DNA directs synthesis of viral components by host cell.

17 4 5 Tail DNA Maturation: Viral components are assembled into virions.
Capsid 5 Release: Host cell lyses and new virions are released. Tail fibers

18 The Lysogenic Cycle: Phage DNA incorporated into host DNA

19 Specialized Transduction
gal gene Prophage Bacterial DNA 1 Prophage exists in galactose-using host (containing the gal gene). Galactose-positive donor cell gal gene 2 Phage genome excises, carrying with it the adjacent gal gene from the host. 3 Phage matures and cell lyses, releasing phage carrying gal gene. gal gene 4 Phage infects a cell that cannot utilize galactose (lacking gal gene). Galactose-negative recipient cell 5 Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA. 6 Lysogenic cell can now metabolize galactose. Galactose-positive recombinant cell

20 Multiplication of Animal viruses
Attachment Viruses attach to cell membrane Penetration By endocytosis or fusion Uncoating By viral or host enzymes Biosynthesis Production of nucleic acid and proteins Maturation Nucleic acid and capsid proteins assemble Release By budding (enveloped viruses) or rupture (non-enveloped viruses)

21 Attachment, Penetration, and Uncoating

22 Release of an enveloped virus by budding

23 Nonenveloped DNA virus
Can cause cancer (cervical cancer) Hand warts Genital warts Commonly sexually transmitted Prevention: vaccine for HPV Respiratory infections in humans Usually sudden onset and short duration Tumors in animals

24 Enveloped DNA virus Can cause chronic liver disease
Can lead to liver cancer Body fluid transmisson Prevention: vaccine Human Herpes Virus 1 and HHV 2 – “cold sores” and genital herpes Sexually transmitted Other direct contact transmission Prevention: condoms (not 100%), abstinence

25 Enveloped DNA virus Varicella-Zoster virus (HHV 3) –
Chicken pox is initial infection Shingles may occur later Contracted by inhaling virus Prevention: vaccine Epstein-Barr virus (HHV 4) – Infectious Mononucleosis Saliva transmission Burkitt’s lymphoma in African children Prevention: avoid infected body fluids (mainly saliva)

26 Multiplication of a Retrovirus
Reverse transcriptase Capsid Envelope Virus Two identical strands of RNA 1 Retrovirus penetrates host cell. Host cell DNA of one of the host cell’s chromosomes 5 Mature retrovirus leaves host cell, acquiring an envelope as it buds out. Reverse transcriptase 2 Its RNA is uncoated; reverse transcription takes place. Identical strands of RNA Viral RNA 4 Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins. Viral proteins RNA 3 The new viral DNA is tranported into the host cell’s nucleus and integrated as a provirus. The provirus may divide indefinitely with the host cell DNA. Provirus

27 Retroviruses – enveloped RNA viruses
Use reverse transcriptase to produce DNA from RNA viral genome HIV - AIDS Oncogenic viruses Some retroviruses can cause cancer

28 Cancer The genetic material of oncogenic viruses becomes integrated into the host cell's DNA. “transform” normal cells into cancerous cells. An oncovirus can promote oncogene expression may contain oncogenes

29 Viral Infections Virus remains in host cell for long periods, asymptomatically Subsequent activation may lead to: i.e. cold sores, shingles Persistent Viral Infections Disease progresses over a long period, generally fatal Subacute sclerosing panencephalitis, SSPE (measles virus) AIDS dementia complex (HIV)

30 Prions Infectious proteins
Inherited, and transmissible by ingestion, transplant, & surgical instruments Spongiform encephalopathies (fatal): Sheep Scrapie, Creutzfeldt-Jakob disease, mad cow disease Cause: normal cellular prion protein on cell surface, converts to scrapie protein, accumulates in brain cells forming plaques

31 Prions PrPSc PrPc 1 2 3 4 Lysosome Endosome 5 6 7 8

32 Plant viruses and viroids
enter through wounds or via insects are infectious RNA One causes potato spindle tuber disease Potato Spindle Tuber Viroids

33 RNA virus, nonenveloped
Poliovirus May be paralytic in ~1% of cases Transmission: Prevention: vaccine Human Number one cause of the common cold Attacks liver, kidneys, spleen Transmission: fecal-oral route Usually not fatal Prevention: vaccine (long-term), immune globulin (short-term)

34 RNA virus, enveloped Influenza viruses A, B, and C Type A have caused
Both type A and B cause seasonal flu Subtypes differ based on H and N spike variation

35 Influenza viruses continued:
Mutation of H and N spike can lead to epidemics or pandemics Contracted by inhaling virus Prevention: vaccine may prevent

36 RNA virus, enveloped Infects birds and humans Transmitted by mosquitos
First appeared in U.S. in 1999 in NYC area; now coast to coast Symptoms: Usually “flu-like;” less than 1% get West Nile Encephalitis Prevention: avoid mosquito bites


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