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Microbiology > Virus Replication Wk2 > Flashcards

Virus Replication Wk2 Flashcards

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Biology 101 flashcards
1
Q

How does virus enter through the skin?

A

Wounds, punctures
Animal/insect bite
Rabies

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2
Q

How does virus enter through eyes?

A

Aerosols, droplets, dust e.g. Herpes simplex virus

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3
Q

How does virus enter through respiratory tract

A

Inhalation e.g. Influenza

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4
Q

How does virus enter through intestinal tract

A

Ingestion, STD e.g. HPV, polio virus

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5
Q

Virus enters mucosal membranes by

A

Direct contact eg. HIV

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6
Q

Iatrogenic

A

Transmission via medical procedures
Shared needle eg. HIV

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7
Q

Vertical transmission

A

From parent to off spring
Breast milk =hiv

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8
Q

Viruses may remain at entry site

A

Skin, gut mucosa

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9
Q

Spread in localised tissues

A

e.g. Regional lymph nodes

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10
Q

Spread systemically to distant organs via blood, lymph neurons

A

Liver, spleen heart, nerves, brain

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11
Q

Attachment protein

A

Viruses bind to cells through their surface proteins

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12
Q

Receptor and co-receptor

A

Attachment protein binds via specific plasma membrane proteins

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13
Q

Cell tropism + host range

A

Cells susceptible to infection

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14
Q

Angiotensin converting enzyme 2 (ACE-2) SARS CoV-2

A

transmembrane protein
Involved in vasodilation

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15
Q

ACE2 is wide spread, respiratory, arterial, renal, cardiac cells

A

Wide cell tropism for virus

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16
Q

Binding of S1 subunit and ACE2 is the virus..

A

Attaching to cells

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17
Q

ACE2 receptor binding domain of spike protein research..

A

Target for drugs and vaccines

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18
Q

Influenza A virus attachment protein = haemagglutinin HA or H

A

Receptor = glycoprotein sugar side chains

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19
Q

Carbohydrate side chains which end with galactose + sialic acid only bind to..

A

Influenza A

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20
Q

Human influenza a bind to disaccharide in a …

A

-2,6 linked conformation
2nd carbon of sialic acid
6th carbon id galactose

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21
Q

Different isometric forms influence virus binding

A

Avian Influenza A viruses bind to the
disaccharide in an -2,3 linked conformation
2nd carbon of sialic acid
3rd carbon of galactose

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22
Q

Some enveloped viruses penetrate by fusion at the plasma membrane

A

HIV
measles
mumps

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23
Q

Many viruses trigger endocytosis, macropinocytosis or micropinocytosis

A

Virus attachment to the specific receptor
stimulates plasma membrane invagination
Virus is captured within a membrane
vesicle – capsid or genome must
escape to enter the cytoplasm
Ebola, rabies

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24
Q

Endocytosis, macropinocytosis & micropinocytosis vesicles
typically fuse with cell endosomes as the next step

A

Virus must escape from the endosome into the cytoplasm

25
Q

Endosome escape mechanisms

A

require the action of a virus
protein, typically activated by low pH (<6.0)

26
Q

Enveloped viruses -

A

fusion of endosome
membrane & virus
envelope

27
Q

Naked viruses -

A

lysis
(complete rupture) of
endosome membrane

28
Q

Enveloped viruses -

A

permeabilization
(localised rupture) of
endosome membrane

29
Q

Uncoating - Virus genome must be released into the cell

A

Plasma membrane, from endosome,into nucleus, through cell wall

30
Q

Very small viruses may pass through a nuclear pore
- capsid degrades / genome uncoats within nucleoplasm

A

Hepatitis B

31
Q

Most viruses degrade capsid outside nuclear pore
- only genome and few proteins enter nucleoplasm

A

Herpes simplex virus

32
Q

Immediate early (IE) genes expression

A
  • cellular RNA polymerase
  • promoters similar to cell promoters
  • transcribed as soon as genome uncoated
33
Q

Delayed early (DE) genes

A
  • cellular RNA polymerase
  • promoters have some similarity to cell promoters
  • transcribed after IE proteins made
  • Modify TFs and/or RNA polymerase
34
Q

Genome replication

A
  • cellular or viral polymerase
  • dependent on early proteins
  • Single or multiple origins
35
Q

Late (L) genes

A
  • cellular or viral RNA polymerase
  • promoters have unique
  • dependent on early proteins
  • mostly virion structural proteins
36
Q

Human immunodeficiency virus is an exception

A

Genome is replicated first then integrated into chromosome
- genome is transcribed from the integrated copy
- all genes expressed from this integrated copy

37
Q

Polio virus is also exception ( no early/ late genes)

A

Polio virus genome acts as mRNA
- all genes are expressed together
at the start (at low levels)
- low levels of all virus proteins
are synthesised
- These are needed to transcribe /
copy the RNA genome
- all genes expressed again after
genome replication

38
Q

Virus genome replication

A

DNA or RNA synthesis = replication of virus genome (many copies made) = enzymes similar to cell DNA & RNA polymerases
= variations of mechanism, dependent on virus genome
- Baltimore classification

39
Q

Assembly & exit of new viruses
assembly = accumulation in cell of large numbers of new virus genomes & new structural proteins
exit
= genomes and proteins associate through specific nucleotide and amino acid sequence regions
= formation of capsids and / or nucleocapsids

A

Exit = lysis, budding or exocytosis
- usually cause the death of cell at some point

40
Q

Baltimore classification

A

= genome structure, replication & transcription strategies

41
Q

Class I dsDNA genome

A

Gene expression
- may use cellular RNA polymerases or encode their own
- mRNA transcribed from dsDNA (both invading and replicated copies)

Genome replication
- Viruses may use cell DNA polymerases or encode their own
- varied mechanisms used by different viruses = theta (bidirectional)
= rolling circle
= strand displacement

42
Q

Class II ssDNA genome +or- sense

A

Gene expression
- may use cellular RNA polymerases or encode their own
- mRNA transcribed from dsDNA intermediate formed during replication

Genome replication
- Viruses may use cell DNA polymerases or encode their own
- strands are replicated sequentially
- second (genome) strand made to high levels

43
Q

Class III dsRNA genome

A

Gene expression
- must encode unique RNA polymerase
- mRNA transcribed from dsRNA intermediate formed during replication

Genome replication
- Relies on virus RNA polymerase
Both strands are replicated simultaneously, in mechanisms similar to those seen for dsDNA replication
NOTE: RNA synthesis = transcription

44
Q

Class IV (+)ssRNA genome

A

Gene expression
- must encode unique RNA polymerase
- mRNA transcribed from (-)ssRNA formed during genome replication

Genome replication Virus RNA polymerase
(+) genome strand copied several times to make (-)strand intermediates
Intermediate (-) strands copied many times to make new (+) genomes

45
Q

Class V (-)ssRNA genome

A

Gene expression
- must encode unique RNA polymerase
- mRNA transcribed from (-)ssRNA genome and genome copies

Genome replication Virus RNA polymerase
(-) genome strand copied several times to make (+)strand intermediates

(+)RNA intermediate strands copied many times to to make new (-) genomes

46
Q

Class VI (+)ssRNA genome

A

Gene expression
- uses cellular RNA polymerase
- mRNA transcribed from dsDNA copy of genome once integrated into cell chromosome

Genome replication Virus DNA polymerase
= reverse transcriptase

(+)RNA genome copied once to (-)strand DNA
(-)strand DNA copied once to yield dsDNA
dsDNA copy ligated into host cell chromosome
(+)RNA genome transcribed repeatedly from integrated dsDNA by cellular RNA polymerase II

47
Q

Class VII dsDNA genome

A

Gene expression
- uses cellular RNA polymerase
- mRNA transcribed from dsDNA genome

Genome replication Cell RNA polymerase Virus DNA polymerase
= reverse transcriptase

Transcription (cell RNA polym,erase II) produces many genomic-length mRNAs (+ssRNA)
Virus reverse transcriptase copies these to yield (-)ssDNA
Same enzyme copies these DNA strands to produce new dsDNA genomes

48
Q

Late gene expression results in

A

high concentrations of virus structural proteins

49
Q

Icosahedral viruses –

A

empty capsids form first & genome molecule packaged

50
Q

Helical viruses –

A

proteins typically assemble around the genome molecule

51
Q

Assembly of helical viruses, tobacco mosaic virus

A

One gene encodes the capsid protein
Multiple copies form a disk
Disks assemble in pairs
Genome associates with one disk
Coat proteins change and disk becomes helix
= locked washer
More disks bind to each side Convert to helix as link
Continue until whole genome enclosed

52
Q

Assembly of icosahedral viruses (polio spontaneously)

A

One gene encodes the 4 capsid proteins, via cleavage of a polyprotein

These bind together to form a hetero-trimer (protomer) – 5 protomers associate togther to form a pentamer

12 pentamers assemble to form an empty structure – a procapsid or provirion

Genome is packaged into this immature provirion, usually through a modified pentamer

53
Q

Assembly of icosahedral viruses (herpes scaffold)

A

Multiple genes encode several capsid proteins, and scaffold proteins
Scaffold proteins allow assembly of a procapsid of structural proteins

Scaffold proteins are subsequently digested, and virus genome enters the structure

54
Q

Many enveloped viruses exit by budding at the plasma membrane (hiv)

A
  1. Capsids migrate to cell membrane, virus glycoproteins accumulate in membrane 2. Capsid proteins interact with glycoproteins and pull membrane around capsid
  2. Membrane “pinches off” when envelopment is complete = exit from cell
    = envelope acquisition
55
Q

Some viruses bud at internal membranes

A
  1. Capsids assembled in the nucleus can bud at the inner nuclear membrane
  2. The new membrane is lost again by fusion with the outer nuclear membrane
56
Q

Budding at ER and Golgi membranes triggers release by exocytosis

A
  1. Capsids bud into the ER or 4. ER / Golgi vesicles bud out during Golgi – gain 1 membrane exocytosis – gain 2nd membrane
    - the 2nd membrane is lost by fusion with the plasma membrane
57
Q

Exit of many non-enveloped viruses is achieved by cell lysis
Polio

A

Cell membrane degrades & contents spill out, including newly-formed virions

58
Q

2

A

Microbiology (9 decks)

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