Viral Structure and Multiplication Flashcards

1
Q

what are the importances of viruses?

A

major cause of disease
important members of the aquatic world
important in evolution due to transfer of genes between bacteria
important model systems in molecular biology

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2
Q

what are bacteriophages?

A

bacterial viruses

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3
Q

what are the main types of viruses?

A

eukaryotic (plants, animals, protists, and fungi)

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4
Q

how are viruses classified into families?

A

genome structure, life cycle, morphology, and genetic relatedness

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5
Q

what is a virion?

A

mature viruses

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6
Q

what do all virions contain?

A

a nucleocapsid composed of nucleic acid (DNA or RNA) and a protein coat

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7
Q

what are capsids?

A

large macromolecular structures which serve as a protein coat of a virus

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8
Q

what is the function of capsids?

A

protect viral genetic material and aid in its transfer between host cells

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9
Q

what are capsids made up of?

A

protein subunits called protomers

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10
Q

what are the three shapes of capsids?

A

helical
icosahedral
complex

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11
Q

helical capsid characteristics

A

shaped like hollow tubes with protein walls

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12
Q

icosahedral capsid

A

regular polyhedron with 20 equilateral faces and 12 vertices
capsomers are ring or knob shaped units made of 5 or 6 protomers

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13
Q

complex capsids

A

do not fit into helical or icosahedral categories

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14
Q

examples of complex capsids

A

poxviruses
large bacteriophages with final symmetry

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15
Q

where do animal virus envelopes arise from?

A

lipids and carbohydrates from the host cell plasma or nuclear membranes

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16
Q

how are viral envelope spike proteins made and what is their purpose?

A

encoded by the virus
involved in viral attachment to the host cell
used for identification of the virus
may have enzymatic activity
may play a role in nucleic acid replication

17
Q

how are viral genomes diverse?

A

viruses can be made of single stranded RNA, single stranded DNA, double stranded RNA, or double stranded DNA
the length varies from virus to virus
genomes can be linear or circular

18
Q

list the steps of the viral multiplication process

A

depends on viral structure and genome, but steps are similar:
1. Attachment to host cell
2. Entry and uncoating of genome
3. Synthesis
4. Assembly
5. Release

19
Q

what occurs during attachment (adsorption)

A

receptor determines host preference
-may be specific tissue
-may be more than one host
-may be more than one receptor

20
Q

what occurs during entry into the host?

A

the entire genome or nucleocapsid enters
varies between naked and enveloped viruses

21
Q

what are the three methods of host entry?

A
  1. Fusion of the viral envelope with the host membrane; nucleocapsid enters
  2. Endocytosis in vesicle; endosome aids in viral uncaring
  3. Injection of nucleic acid (non enveloped)
22
Q

what occurs during the synthesis stage?

A

all viral components are produced
genome dictates the events
-RNA viruses must carry in or synthesize the proteins necessary to complete synthesis
genes and proteins may be referred to as early, middle, or late based on when they are synthesized

23
Q

what occurs during assembly?

A

putting together all components to make complete virions
assembly process is complex
baseplate, tail fibers, and components of bacteriophage T4 are assembled separately

24
Q

what occurs during virion release?

A

Non-enveloped viruses lyse the host cell
viral proteins may attack peptidoglycan or membrane

25
how does virion release occur in enveloped viruses?
viral proteins are incorporated into the host membrane nucleocapsid may bind to viral proteins envelope derived from host plasma membrane, but may be Golgi, ER, etc. Virus may use host actin tails to propel through host membrane
26
what are the two types of phages and their reproductive choices?
virulent phage- multiplies immediately upon entry and lyses bacterial host cell temperate phage- reproduce lytically as virulent phages do or remain in the host cell without destroying it
27
what is lysogeny?
a relationship in which many temperate phages integrate their genome into host genome, making them a prophage in a lysogenic bacterium
28
what is an advantage of a virus having a lytic cycle?
faster production, therefore there is faster infection
29
what is an advantage of a virus having a lysogenic cycle?
if the environment is bad without other host cell options, the virus can stay and wait for another choice
30
how does infection in eukaryotes work?
cytocidal infection results in cell death through lysis persistent infections can last for years- chronic the cell can transform into a malignant cell and cause tumor formation
31
what are viroids?
infectious agents comprised only of RNA typically targets plants lacks an outer protein layer/capsid
32
what are satellites (virusoids)?
infectious agents comprised of nucleic acids and a protein coat needs a co-infector to replicate can infect both plants and animals
33
what are prions?
protein viruses that cause a variety of neurodegenerative diseases in humans and animals
34
what are diseases caused by prions called and give examples
transmissible spongiform encephalopathies -scrapies in sheep -mad cow disease -chronic wasting disease in deer -kuru and Creutzfeldt-Jakob disease in humans