Viruses and other Acellular Biological Entities, Viroids ...faculty.sdmiramar.edu/bhaidar/Bio 107...

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Viruses and other Acellular Biological Entities, Viroids, & Prions (Outline) Acellular entities as disease agents: viruses, viroids, and prions Contrast structure and properties of viruses with living cells Parasitic nature of viruses: Host-cell specificity: relate to common human diseases Insertion of some viral genomes into host DNA Ebola Virus: Zika Virus Retroviruses and their life cycle (example: HIV) Role of ancient and current retroviruses in major evolutionary steps and in shaping animal genomes. Role of ancient and current viral infections as selective pressure affecting human genetic variability

Transcript of Viruses and other Acellular Biological Entities, Viroids ...faculty.sdmiramar.edu/bhaidar/Bio 107...

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Viruses and other Acellular Biological Entities,Viroids, & Prions

(Outline)

• Acellular entities as disease agents: viruses, viroids, and prions• Contrast structure and properties of viruses with living cells• Parasitic nature of viruses:

– Host-cell specificity: relate to common human diseases– Insertion of some viral genomes into host DNA

• Ebola Virus: Zika Virus• Retroviruses and their life cycle (example: HIV) • Role of ancient and current retroviruses in major evolutionary steps

and in shaping animal genomes. • Role of ancient and current viral infections as selective pressure

affecting human genetic variability

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Acellular Disease-causing infectious biological entities(Health Connection)

Virus-Packaged genetic material in transit for one host cell to the next

Viroid-Circular naked RNA

Prion-Mis-folded infectious proteins

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Viroids and Prions: The Simplest Infectious Agents

• Viroids - infect plants and disrupt their growth-Cadang-Cadang of coconut trees

• Prions -slow-acting, indestructible infectious proteins that cause brain diseases in mammals (mad cow disease, ; Kuru- Fore tribe of Papua New Guinea; Scarpie in sheep)

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Viruses are nucleic acids (genes) packaged in protein

– Biological non-living entities– Have no cytoplasm – Cannot self-replicate– Cannot metabolize– Genetic material either

DNA or RNA never both

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Viruses

• To replicate they need to infect a living cell• Every living cells has one or more viruses that

can infect it, specifically• Phage: a virus that infect bacterial cells to

reproduce using the machinery of bacterial cellshttps://www.youtube.com/watch?v=3Ms04x6MvMY (First 3 mins of “The Virus Hunters” DVD)

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RNA

Capsomere

Capsomereof capsid

DNA

Glycoprotein18 250 nm 70–90 nm (diameter)

Glycoproteins80–200 nm (diameter) 80 225 nm

Membranousenvelope RNA

Capsid

HeadDNA

Tailsheath

Tailfiber

50 nm50 nm50 nm20 nm(a) Tobacco mosaic

virus(b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4

Naked EnvelopedComplex

Viral Shapes

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Basis of Host-Range of Viruses

• Host range is determined by “lock-and-key” fit between virus surface and cellular receptors on host cell

• Most viruses infect only specific types of cells in one host Narrow host range with tissue specificity – cold viruses: upper respiratory tract cells.– HIV, AIDS virus: a certain white blood cell.

• Some have a broad host-range infecting multiple species – rabies

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Animal Virus Life Cycle

• Attachment• Entry • Uncoating of virion

separate protein from NA• Replication of nucleic

acid and synthesis of viral proteins

• Maturation of virions(assembly of NA and proteins)

• Release: cell lysis or budding

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Membranousenvelope

RNA

Proteincoat

Glycoprotein spike

Viral genomes are made of either DNA or RNA– Flu viruses are RNA– Genital warts virus (HPV) and Herpes virus are DNA

viruses

HPVInfluenza

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Emerging viruses threaten human health

Colo

rized

TEM

50,

000×

Colo

rized

TEM

370

,000×

Figure 10.20A, B

Ebola Virus (RNA) SARS Virus (RNA)

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Zika Virus

• http://www.microbiologyinfo.com/zika-virus-structure-genome-symptoms-transmission-pathogenesis-diagnosis/

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Ebola virus– An enveloped RNA (- strand)Entry and exit– http://www.youtube.com/watch?v=57P6MuM3_F8

LinksCenters for Disease Control and Preventionhttp://www.cdc.gov/vhf/ebola/transmission/index.html?s_cid=

cs_284WHOhttp://www.who.int/mediacentre/factsheets/fs103/en/

Zika Virushttp://www.cdc.gov/zika/about/

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Retroviruses

https://www.youtube.com/watch?v=3Ms04x6MvMY (min 3 -12)

The Virus Hunters (DVD)• Retroviruses in human genomes

(first 12:30 mins)

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The AIDS virus– HIV is an RNA retrovirus– It makes DNA using RNA template– Inside a cell, HIV uses its RNA as a template to make a DNA

copy of itself, which integrates into the host genome.http://www.susanahalpine.com/anim/KubyHTML/HIV.htm

Envelope

Glycoprotein

Protein coat

RNA (two identical strands)

Reverse transcriptase

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About 8% of our genome is derived from RNA retroviruses- Evidence of past infection- Sequences tend to increase over time

Viral DNA

Figure 11.11

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Roles of human endogenous retroviruses

Endogenous retroviruses• Placenta formation• Large Brain development • Powerful emotions

Explorer: The virus hunters (DVD)https://www.youtube.com/watch?v=xtnejNGOONkhttps://www.youtube.com/watch?v=3Ms04x6MvM

Y

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Role for Viruses in shaping the Human Genome

• Past retroviral infection in a primate ancestor – Insertion of sequences– New proteins or protein domains for host that

maybe beneficial and influence behavior

• Present retroviral infections are a selective pressure acting on the genetic variability of the human population