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Microbiology > Lecture 11 > Flashcards

Lecture 11 Flashcards

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Biology 101 flashcards
1
Q

Virion

A

an individual virus

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2
Q

Virus

A

non-living? acellular
metabolically inert
- no energy generation or biosynthesis
- when outside cells not generating ATP
extracellular and intracellular forms

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3
Q

virus genomes

A

RNA or DNA
single or double-stranded
very small, few genes (use host genes)

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4
Q

capsid

A

protein shell
surrounds and protects genome
- arranged in a precise, repetitive pattern
- single or multiple protein types
- capsomeres (dictate symmetry)

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5
Q

Icosahedral symmetry

A

= spherical virus

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6
Q

helical symmetry

A

= rod shaped virus

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7
Q

complex virus

A

icosahedral head and helical tail
- bacteriophage

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8
Q

naked viruses

A

genome + capsid
- bacteriophages (mostly)

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9
Q

enveloped

A

contain an additional membrane
- surrounds the nucleocapsid
- composed of a lipid bilayer and proteins
- common in viruses that infect animals (use membrane to get in/out of host cells)

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10
Q

viral enzymes

A

for functions not provided by host cell enzymes
- an invasion of the host cell (lysozyme– to get through peptidoglycan layer)
- viral replication of RNA (reverse transcriptase– RNA to DNA)

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11
Q

viral diversity

A

infects all forms of life
sputnik virophage example

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12
Q

viral shunt

A

role of viruses in global nutrient cycles
- movement of elements in ocean example

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13
Q

plaque assay

A

used in lab to quantify viruses
plaques = clear areas around lysed host cells
count the plaque forming units PFUs

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14
Q

viral replication steps

A
  1. attachment
  2. penetration
  3. synthesis
  4. assembly
  5. release (lysis)
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15
Q

Attachment

A

proteins on virion capsid or membrane
- bind to surface receptors of host cells
determines the specificity of the virus
- no receptor = no attachment
- among hosts and within multicellular hosts (ex flu virus only in upper respiratory tract)

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16
Q

Penetration

A

bacterial viruses (bacteriophage)
- tail fibers (attaches to the outer membrane and retracts)
- tail core (contacts cell wall and releases lysozyme)
- viral DNA (enters the cell through cell wall whole)

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17
Q

Synthesis

A

two steps:
1) replicate the viral genome
2) synthesize proteins
Speed depends on the type of viral genome
- Baltimore classification scheme

18
Q

Baltimore classification scheme

A

seven classes of viruses
based on the viral genome

19
Q

DNA viruses

A

dsDNA -> mRNA -> protein
ssDNA -> dsDNA -> mRNA -> protein

20
Q

RNA viruses

A

ssRNA (+) = mRNA -> protein
ssRNA (-) = mRNA -> protein
* need to bring enzymes with them

21
Q

RNA retroviruses

A

ssRNA (+) -> dsDNA -> mRNA -> protein
* need to bring enzymes with them

22
Q

RNA-dependent RNA polymerase

A

“RNA replicase”
RNA replication (RNA -> RNA)

23
Q

reverse transcriptase

A

RNA -> DNA

24
Q

Synthesis and viral proteins

A

early proteins: aid replication of viral genomes
late proteins: aid construction of viral capsid

25
Q

Assembly

A

nucleocapsids formed by self-assembly

26
Q

Release

A

depends on the viral life cycle
- lytic (virulent) mode
– host cells lysed and killed
- lysogenic (temperate) mode
– host cells remain intact

27
Q

Lytic pathway

A

viral replication
cell lysis -> virions released

28
Q

Lysogenic pathway

A

viral DNA -> host DNA
replicates with host cell

29
Q

bacteriophage lambda

A

prophage
- virus genome in the host chromosome
lysogen
- bacterial cell with the viral genome
ecological significance
- new genetic properties
- immunity to related viruses

30
Q

Animal viruses

A

entire virion enters the host cell
virion must enter the nucleus of the host cell
virion can exit without cell lysis (“budding”)
- virulent, persistent, and latent infections

31
Q

virulent infections

A

viral replication
- cell lysis -> all virions released

32
Q

persistent infections

A

viral replication
- no cell lysis -> some virions bud

33
Q

latent infections

A

no viral replication
- no cell lysis -> no virions released

34
Q

antiviral mechanisms

A

attachment and penetration
- nearly impossible to prevent
- viruses attached to surface receptors of host cells need for normal cell functioning
synthesis is the actual antiviral target

35
Q

synthesis antiviral mechanism

A

target and destroy viral genome
- restriction endonucleases (enzymes that cut/break DNA)
RNA-based defense systems
- CRISPR (prokaryotes)
- interference RNA (eukaryotes)

36
Q

Restriction endonucleases

A

only in prokaryotes
recognize and digest foreign DNA
cut DNA at specific nucleotide sites
high degree of specificity, important to not harm own DNA

37
Q

Restriction modification system

A

methylate own DNA as protection
prevents digestion of self DNA

38
Q

CRISPR

A

clustered regularly interspaced short palindromic repeats (viral sequence “archive”
library of previous infections

39
Q

RNA interference (RNAi)

A

CAS proteins
- identifies dsRNA (= viral infection)
- cuts dsRNA into pieces
- uses pieces to target and destroy viral mRNA

40
Q

Dicer

A

cleaves dsRNA into shorter segments

41
Q

RISC

A

binds siRNA and separates the strands
finds messenger RNA complementary to siRNA
cleaves mRNA
RNA fragments degraded by exonuclease

Microbiology (19 decks)

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