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MICR2208 > Lec 12: Virology > Flashcards

Lec 12: Virology Flashcards

1
Q

Properties of virus

A

RNA or DNA

Do not grow by binary fission or other forms of cell division

Do not have organelles

Do not have ATP generating mechanism (require live host cell)

Most infect eukaryotic cells

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2
Q

Bacteriophage (phages)

A

Bacterial viruses

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3
Q

Family classification

A

Genome structure

Life cycle

Morphology

Genetic relatedness

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4
Q

Virus structure

A

Contain nucleocapsid: composed of nucleic acid (DNA or RNA) & protein coat (capsid)

Some have additional components: envelope, spike, capsid, nucleic acid

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5
Q

Capsid

A

Large macromolecule structures -> protein coat for virus

Protects viral genetic material & aids its transfer between host cells

Made of protomers (protein subunits) -> aggregate -> capsomeres

Helical, icosahedral or complex

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6
Q

Helical capsids

A

Shaped like hollow tubes with protein walls -> enclose nucleic acid

Protomers self assemble -> form rigid tube

Size of capsid depends on length of nucleic acid

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7
Q

Icosahedral capsid

A

Regular polyhedron with 20 equilateral faces & 12 vertices -> efficient way to enclose space

Capsomers: ring or knob shaped units made of 5 or 6 protomers. Pentamers (pentons)- 5 subunit capsomers. Hexamers (hexons)- 6 subunit capsomers

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8
Q

Viral envelopes

A

Outer, flexible, membranous layer

Make virus susceptible to certain disinfectants

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9
Q

Envelope proteins

A

Encoded by virus

May project from envelope surface as spikes (peplomers)

Involved in viral attachment to host cells

Used for identification of virus

May have enzymatic or other activity

May play role in nucleic acid replication

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10
Q

Viral genome

A

Diverse

Virus may have single or double stranded DNA or RNA

Length of nucleic acid varies

Can be segmented or circular

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11
Q

Requirements for viral replication

A

Living cell

Receptor to allow virus to enter cell

A way to leave cell

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12
Q

Viral replication

A

Attachment: virus attaches to cell membrane

Penetration by endocytosis or fusion

Uncoating by viral or host enzymes

Biosynthesis: production of nucleic acid & proteins

Maturation: nucleic acid & capsid proteins assemble

Release by budding (enveloped viruses) or rupture

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13
Q

Viral attachment

A

Virus must interact with host cell receptor

If receptor present on cells of numerous animals-> virus can infect multiple species

Some viruses have specific hosts

Some viruses only infect specific cells within complex eukaryote

No receptors for plant viruses

Damage of host cells -> virions transfer between plants

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14
Q

Middle proteins

A

Involved with replication of genome

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15
Q

Late proteins

A

Involved with self-assembly or capsid

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16
Q

Retrovirus replication

A

Can produce ‘provirus’ -> integrates into host DNA & replicated along with host DNA (silent infection)

-> virus exist indefinitely in host genome

When coming out of latency -> provirus directs replication of new RNA strands, capsid & envelop proteins

17
Q

Retroviruses

A

Convert ssRNA to dsDNA using reverse transcriptase

dsDNA integrates into host cell genome. Serves as template for mRNA synthesis & genome synthesis

18
Q

Virulent phage

A

One option: begin multiplying immediately upon entering bacterial host -> lyse bacterial host cell

19
Q

Temperate phage

A

Two options

Entry: multiply like virulent and lyse host cell or can remain in host without destroying

Many integrate genome into host genome in relationship called lysogeny

Changes phenotype of host. Bacteria becomes immune to superinfection. Phage may express pathogenic toxic or enzymes

20
Q

Advantages to lysogeny

A

Phage remains viable but may not replicate

If there are more phages than host cells, lysogeny ensures survival of host -> continue to replicate and replicate integrated phage DNA

21
Q

Lysogeny

A

Infected bacteria will lyse and release phage particles under appropriate conditions

Conditions in cell -> prophage initiates synthesis of new phage particles: induction

Cause: change in growth conditions or UV-irradiation of host cell

MICR2208 (13 decks)

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