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Microbiology & Immunology > 25-27 - Virology (Virus structure, transmission and replication)) > Flashcards

25-27 - Virology (Virus structure, transmission and replication)) Flashcards

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Biology 101 flashcards
1
Q

Viruses are obligate…

A

Intracellular parasites

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2
Q

A purified virus particle is known as a…

A

Virion

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3
Q

Virions can be seen using…

A

Electron microscopy

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4
Q

Outline the basic structure of a virus…

A
  • Genome (DNA/RNA DS/SS) within nucleocapsid
  • Protein capsid comprised of subunits (capsomeres)
  • An envelope (host cell phospholipid membrane)
  • Surface or envelope proteins
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5
Q

Give 3 approaches to the classification of viruses…

A
  • Morphology
  • Biology (tissue type)
  • Genome organisation & replication (Baltimore classification)
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6
Q

The Baltimore classification (Classes 1-7) groups viruses based on their routes to the production of mRNA.

Broadly, DNA viral genomes can be transcribed by host polymerases, however RNA viruses…

A

Must encode their own RNA dependent polymerases (although some RNA viruses (retroviruses) use reverse transcriptase to generate DNA)

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7
Q

What is a sub-virus? Give 4 examples…

A

Sub-viruses are virus like entities that fail to meet some of the minimum criteria for a true virus.

Examples include:

  • Satellite viruses (requires helper virus)
  • Virusoids (genome lacks code for structural proteins, requires helper virus)
  • Viroid (naked infectious RNA)
  • Prions (infectious proteins- BSE, CJD)
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8
Q

Outline the cycle of infection…

A
  • transmission
  • entry
  • primary site replication
  • spreading within host
  • shedding
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9
Q

Outline 5 routes of horizontal transmission…

A
  • Respiratory
  • Fecal/oral (gastrointestinal)
  • Sexual
  • Urinary
  • Mechanical (needles, piercing, surgery etc)
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10
Q

Give 3 examples of viruses transmitted via the fecal/oral route…

A
  • Rotaviruses (vomiting, diarrhea, fever)
  • Hepatitis A (liver inflammation, jaundice)
  • Poliovirus (1% of cases cause irreversible muscle paralysis)
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11
Q

Give 4 examples of viruses transmitted sexually…

A
  • HIV
  • Hepatitis B (HBV) (may become chronic and lead to liver cancer)
  • Human Papilloma Virus (HPV) (Types 16 & 18 - cervical and penile cancer)
  • Herpes Simplex Virus (HSV) (genital blisters, latent infection)
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12
Q

Urinary transmission is very rare. Give the reason why and 2 examples of viruses which can nonetheless be transmitted this way…

A

Rare due to glomerular filtration

Examples: Cytomegalovirus, poliovirus

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13
Q

Mechanical transmission is typical for which type of viruses?

A

Blood-borne

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14
Q

Vertical transmission is transmission from…

(and how might this occur?)

A

Mother to child

This may be transplacental (as in Rubella)

During birth (as in Herpes)

After birth (via breastmilk or saliva)

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15
Q

Transmission of viruses from animal to man is known as…

A

Zoonosis

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16
Q

The animal that acts as a reservoir for a zoonotic virus is known as the…

A

Primary host

17
Q

The animal that transmits a zoonotic virus is known as the…

A

Vector

18
Q

Give two examples of zoonosis, stating the primary host and the vector…

A
  • Rabies virus
    • Fox is both primary host and vector
  • Yellow fever virus
    • Primates act as primary host
    • (Female) mosquitos act as vector
19
Q

Preventing transmission is crucial to controlling viral infections.

List 7 environmental and social factors that influence viral transmission…

A
  • Sanitation (poor sanitation -> fecal/oral transmission)
  • Climate (viral vectors, human behaviours etc)
  • Viral vectors (such as mosquitos-> zoonotic transmission)
  • Poverty (higher likelihood of poor health, lack of access to healthcare etc)
  • Behaviours (intravenous drug use -> mechanical transmission)
  • Population density (faster spread)
  • Healthcare (availability and quality)
20
Q

Outline the 6 stages of viral multiplication…

A
  1. Attachment
  2. Penetration
  3. Uncoating
  4. Biosynthesis
  5. Assembly
  6. Release
21
Q

6 Stages of Viral Multiplication

1. Attachment

Attachment occurs when viral surface proteins gain access to host cells via cell surface proteins, which in this case are known as…

A

Virus receptors

22
Q

The virus receptors on the host cell are problematic as drug targets because…

A

They serve an important functions for host cells

23
Q

6 Stages of Viral Multiplication

2. Internalisation

State and distinguish between the two means of viral internalisation…

A

a) Fusion From Without - entry by fusion of viral envelope w/ plasma membrane
b) Receptor Mediated Endocytosis - entry by endocytosis (after which virus escapes the endosome, by envelope fusing with endosome, or via pore if non-enveloped)

24
Q

6 Stages of Viral Multiplication

3. Biosynthesis

Biosynthesis can be divided into 3 processes…

A
  1. Replication of the genome
  2. Packaging of genome
  3. Altering metabolism of host cell
25
Q

6 Stages of Viral Multiplication

3. Biosynthesis

Viruses must compete for host cell ________ .

Many viruses have evolved mechanisms to outcompete ____ ____, such as _____ - which allows translation of viral mRNA without ____________ .

A

6 Stages of Viral Multiplication

3. Biosynthesis

Viruses must compete for host cell ribosomes.

Many viruses have evolved mechanisms to outcompete host mRNA, such as IRES - which allows translation of viral mRNA without the presence of a 5’ cap.

26
Q

Virally infected cells often inhibit protein synthesis. This can be due to either the virus itself or…

A

Interferon released in response to the virus

27
Q

Viral proteins are also subject to post-translational modifications (such as glycosylation, acylation and lipoylation).

Some viruses encode a polyprotein.

Give an example of a virus that encodes a polyprotein and state how this is modified post-translationally.

A

Hepatitis C encodes a polyprotein.

Post-translational modification breaks up the polyprotein

28
Q

Name the 5 structural forms of virus…

A
  • Naked icosohedral
  • Naked helical
  • Enveloped icosohedral
  • Enveloped helical
  • Complex
29
Q

6 Stages of Viral Multiplication

5. Release

State the 3 ways viruses may be released from the host cell…

A
  • Budding
  • Cell Lysis
  • Cell to Cell (pores or membrane fusion)
30
Q

Enveloped viruses aquire their membranes from…

A

Host cell lipid bilayers (usually plasma membrane when budding)

31
Q

What condition present in the endosome may trigger envelope fusion with or breach of the virus-containing endosome?

A

Low pH

32
Q
A

Microbiology & Immunology (17 decks)

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