Ch. 13 - Viruses

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52 Terms

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Describe viruses

  • Obligate intracellular parasites

  • Infect specific cell receptors

  • 30 nm (smaller than bacteria)

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Characteristics of viruses

  • Outside capsid layer & some have a lipid envelope

  • Inside are genomes & proteins (either DNA or RNA, never both)

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What are viruses sensitive to?

Interferons

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What are the 4 morphological types of viruses?

  • Helical

  • Polyhedral

  • Complex

  • Enveloped

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Helical viruses

Cylindrical

  • Rabies

  • Ebola

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Polyhedral viruses

Equilateral triangle

  • Adenovirus

  • Poliovirus

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Complex viruses

Bacteriophage, alien-rocketship thing

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Enveloped viruses

  • May be covered in spikes

  • Glycoproteins for attachment

    • COVID

    • Influenza

    • Herpes

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Naked viruses

No lipid coat outside capsid

  • Rhinovirus

  • Poliovirus

  • Norwalk

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Viruses grow in

Living cells

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How are viruses seen on a plate?

Bacteriophages form plaques on a lawn of uninfected bacteria

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Virus multiplication

  • Invade a host cell

  • Take over the hosts’ metabolic machinery

  • One-step growth curve

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Difference between lytic & lysogenic cycle

  • Lytic cycle will destroy the hosts’ DNA & replace it with their own

  • Lysogenic cycle integrates their DNA into the hosts’ cell’s

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Order of multiplication of bacterial virus

  1. Attachment

  2. Penetration

    • Replication, transcription, translation

  3. Biosynthesis

  4. Maturation

  5. Lysis

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Phage conversion in lysogeny cycle

Host acquires new properties from the introduction of the viral DNA

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Order of multiplication of animal viruses

  1. Attachment

  2. Penetration

  3. Uncoating

  4. Biosynthesis

  5. Maturation

  6. Release

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Attachment in animal viruses

Spikes recognize receptors

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Penetration in animal viruses

Endocytosis or fusion

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Uncoating in animal viruses

Release genetic material

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Biosynthesis in animal viruses

DNA/RNA biosynthesis & multiplication

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Maturation in animal viruses

Assembly of new viral particles

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Release in animal viruses

Budding or rapture

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Result of budding in release of an animal virus

Original host cell remains alive & new cell obtains an envelope

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Result of rapture in release of an animal virus

Original host cell dies & new cell has no envelope (naked)

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Difference between bacteriophages & animal viruses

Bacteriophages

  • Attach with tail fibers

  • Viral DNA is injected

  • Activities occur in cytoplasm

Animal Viruses

  • Attach with glycoproteins

  • Capsid enters via endocytosis or fusion

  • Activities either in nucleus (DNA) or cytoplasm (RNA)

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Genome multiplication

  1. Replication (double stranded DNA)

  2. Transcription (RNA: +/sense strand —- DNA: -/anti-sense strand)

  3. Translation (+/sense strand is read)

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DNA polymerase

Used in replication

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RNA polymerase

Used in transcription

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Does mRNA use the template -/+ strand?

Non-template strand (+/sense strand)

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Polymerases in viral replication

DNA

  • Use host cell polymerase

  • Code for their own DNA polymerase & transcriptase

RNA

  • Use host cell polymerase

  • Code for their own DNA polymerase

  • Carry their own polymerases

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Reverse transcriptase

Using RNA to make DNA

  • HIV

  • Leukemia viruses

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dsDNA

Double stranded DNA

  • Herpes

  • HPV

  • Smallpox

  • Adenovirus

  • Hepatitis B-virus

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ssDNA

Single stranded DNA

  • Parvovirus

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ssRNA -

Single stranded RNA w/ the -/anti-sense strand

  • Measles

  • Influenza

  • Ebola

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ssRNA +

Single stranded RNA w/ the +/sense strand

  • SARS coronavirus

  • Rhinovirus

  • Hepatovirus

  • Poliovirus

  • Rubella

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dsRNA

Double stranded RNA

  • Rotavirus

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Retroviruses

ssRNA; converts RNA to DNA using reverse transcrptase

  • HIV-1 (AIDS virus)

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dsDNA replication

  • Largest group of known viruses

  • Replicates in host nucleus

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ssDNA replication

Replicates in host nucleus

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ssRNA+ replication

  1. RNA polymerase takes ssRNA+ & converts it to ssRNA-

  2. Then it converts it back to ssRNA+

  3. ssRNA+ makes new capsid proteins

    • Assembled in cytoplasm

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ssRNA- replication

  1. RnA-dependent RNA polymerase converts ssRNA to ssRNA+

  2. ssRNA+ makes more ssRNA- & continues

    • In cytoplasm

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dsRNA replication

Separated to ssRNA+ & ssRNA -

  • In cytoplasm

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Retrovirus replication

  1. Uses reverse transcriptase to use ssRNA to make dsDNA

  2. dsDNA goes to nucleus & integrates into host genome

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Oncogenic viruses

Cancer

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What do oncogenes do?

Make cells replicate uncontrollably

  • Loses contact inhibition

  • Glycoproteins can’t signal to stop multiplying

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How do you see if you have cancer with the virus?

Presence of:

  • Tumor Specific Transplantation Antigens (TSTA)

  • T antigens in nucleus

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Oncogenic DNA viruses

  • Human Herpesvirus

  • Papillomavirus

  • Hepatis B virus

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Oncogenic RNA viruses

Retrovirus

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Acute viral infection

  • Virus in bloodstream

  • Sudden onset

    • Influenza

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Latent viral infection

Virus remains in asymptomatic host cell for long periods

  • HIV

  • AIDS

  • Leukemia

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Recurrent viral infection

Infection reoccurs

  • Shingles

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Persistent viral infection

Occurs over a long period of time

  • Cancer

  • AIDS