Chapter 13 Flashcards Preview

BIO111: Microbiology > Chapter 13 > Flashcards

Flashcards in Chapter 13 Deck (103):
1

Virus Characteristics

- Obligate intracellular parasitic molecules
- non-motile
- non-living
- over 6,000 known to man

2

Structure of Viruses

- DNA or RNA
- linear or circular
- single or double stranded
- code for enzymes like DNA or RNA polymerase and enzymes to make rest of virus particle

3

Cell Structure
(Virus)

do not have organelles or ribosomes
-only protein and nucleic acids

4

Metabolism
(virus)

require host for synthesis of nucleic acid and proteins

5

Nucleic acids
(virus)

contain DNA or RNA, either single or double stranded

6

Genes
(virus)

have 4- 200 genes

7

bacteria # of genes

3000

8

humans have ____ genes

30,000

9

Size
(virus)

viruses are 100-1000x smaller than cells

10

Capsid

- found in all viruses
- made of protein subunits called CAPSOMERES
-carries enzymes needed for infection

11

Common virus shapes

Icosahedral
Helical
Complex

12

Icosahedral

20 sided polygon
20 triangles, 12 corners

13

Helical

rod-shaped capsid

14

Complex
(shape)

ex. T4 phage: icosahedral head and tail of helical arranged proteins

15

Envelope

lipid bilayer outside of capsule
- only in some viruses

16

Naked viruses

lack envelope, most phages

17

Enveloped viruses

envelope surrounds capsid
-disinfectants damage envelope making virus non-infectious
- matrix proteins found between envelope and capsid, give different shapes to virus

18

Spikes

-protein structures that allow virus to attach to host
- on capsid, envelope, or tail
- virus subtype based on spikes

19

purpose of capsid and envelope

protect the nucleic acid from enzymes and toxic chemicals
ex. polio virus - naked virus can survive GI tract

20

purpose of spikes and capsid

allow virus to attach to host cell
(capsid has special proteins for naked cells to help it attach)

21

Classification and Naming of Viruses

- not classified as a kingdom or domain because not living

22

Two superfamilies

DNA or RNA
human viruses 7 DNA families, 13 RNA families

23

Family names end in

-viridae

24

Genus names end in

-virus

25

Enteric viruses

transmitted by fecal- oral route
ex. polio

26

Zoonotic viruses

transmitted to humans by animals
ex. rabies, cow pox

27

Arboviruses

arthropod borne viruses
ex. west nile

28

bacteriophages

viruses that infect bacteria
AKA phages

29

Characteristics used in classification

- Genome structure
-type of host
- shape of capsid
- overall size
- presence of cell envelope
- how virus affects host cell

30

Potential relationship of virus with host

1. Productive state
2. Latent or Lysogenic State

31

Productive state types

Lytic
Chronic

32

Latent or Lysogenic state types

Latent = animal cells
Lysogenic = bacteria cells

33

Lytic

Productive
Host cell is destroyed by lysis when new viruses released
ex. HIV and lymphocytes

34

Chronic

Host cell survives and continues to divide while releasing viruses
ex. HIV and macrophage

35

Productive Lytic - Bacteriophage
(T4 virus)

T4 = double stranded DNA viruse, infects E.coli
1. Attachment/Adsorption
2. Penetration/ Genome entry
3. Synthesis
4. Assembly
5. Release

36

Attachment/Adsorption

-viruses non-motile so they collide with host by chance
- infection depend on specific receptor sites on outside of host cell

37

Where are receptor sites located on bacteria and animal cells

bacteria - cell wall, flagella and pili
animal cell - cell membrane

38

type of organisms of cell types that virus can infect, usually very specific

Host range

39

Penetration/Genome Entry
(bacteria)

-viral nucleic acids enter host cell
- enzyme lysozyme from tip of T4 virus tail digest part of E.coli cell wall.
-Tail contracts and phage DNA injected through cell wall and cell membrane to cytoplasm
- capsid remains outside of host cell

40

Synthesis
(bacteria)

Synthesis and transcription of viral DNA and production of new viral parts
- uses machinery of host cell (ribosomes, some enzymes) to make "phage-encoded" proteins

41

types of "phage-encoded" proteins

Early proteins
late proteins

42

Early proteins

nuclease that destroys host cell DNA, proteins that modify host RNA polymerase - so no host proteins are made

43

Late proteins

structural proteins to make capsid and tail

44

Assembly
(bacteria)

-virus particles assembled into mature viruses
-some parts assemble spontaneously
- other parts require extra enzymes and proteins for assembly

45

Release
(Bacteria)

- mature viruses are released
- phage-encoded LYSOZYME starts digestion of cell wall from inside
- osmotic pressure causes cell to lyse break
- viruses are expelled

46

Burst size

number of phages released
about 200 for T4 viruses

47

Attachment/adsoption
(Animal)

-Virus recognizes and attaches to host
- Spikes on virus bind to specific receptor sites on host membrane
- in animals, often are two different receptros proteins
- receptors usually have a different purpose for the host
ex. rabies attaches to Acth receptor of nerve cells

48

Penetration/uncoating
(animal)

- in animals the whole virus enters the host cell (in bacteria just the nucleic acid enters)
- Two methods:
Endocytosis and fusion

49

Endocytosis

- whole virus is moved into cell by endocytosis
- virus is engulfed in a vesicle made by host
- occurs with naked and enveloped viruses
- uncoating- host enzymes dissolve capsid and envelope and nucleic acids are released

50

Fusion

-Viral envelop fuses with host cell membrane
- only capsid and genome enter host
- uncoating occurs to release nucleic acid

51

Steps of animal productive lytic

1. Attachment (adsorption)
2. Penetration (genome entry) (uncoating)
3. Synthesis -> nuclease (breaks down nucleic acids)
4. Assembly
5. Release (budding) enveloped viruses

52

Synthesis

- Synthesis and transcription of viral nucleic acid and production of new viral parts using machinery of host cell just as in phages
- genome is expressed and copied
-viral enzymes made
- capsomeres and spikes made

53

Synthesis DNA viruses

Double stranded - "normal" mechanisms
Single stranded - made into double stranded before transcription

54

Synthesis RNA viruses

Single and Double stranded - viral enzyme REPLICASE (RNA polymerase) makes new RNA for new viruses, replicases do not proof-read like DNA polymerase which explains mutations of influenza virus

55

Synthesis (Revers Transcriptase)

-Some viruses have complex system of genome sythesis
ex. RETROVIRUSES (including HIV)
- Viral RNA is made into DNA using viral encoded enxyme called REVERSE TRANSCRIPTASE
- this double stranded DNA is incorporated into host DNA
- Virus can become productive or latent

56

Assembly
(animal)

- virus particles assembled into mature viruses
- if the virus is enveloped, then spikes are placed within the cell membrane of the cell

57

Release
(animal)

Mature viruses are released
- human virus burst size = 3,000 - 50,000 viruses/one cell
- enveloped vs. Naked viruses

58

Enveloped Viruses
(Release- Animal)

- Budding
- viruses released slowly, host cell usually not destroyed
- Host cell can be damaged

59

Budding

vesicle (from cell membrane or Golgi) surrounds virus, spikes added to membrane

60

Ways host cell can be damaged in release of enveloped viruses

- Shutdown of metabolism and genetic expression
- Destruction of cell or organelle membranes
- toxicity of viral components

61

Naked virus - release
(Animal)

- Cell fills with viruses
- spontaneously lyses
- Release can be caused by virus triggering normal host immune responses
- host cell death

62

Productive Chronic Bacteriophage

-M13 filamentous, single stranded DNA phage
- virus released without killing host cell

63

4 steps of Productive Chronic Bacteriophage

1. Attachment
2. Penetration
3. Synthesis
4. Assembly

64

Attachement
(Bacteriophage)

attaches to F pilus

65

Penetration
(Bacteriophage)

injects DNA through pilus to cytoplasm

66

Synthesis
(Bacteriophage)

Host DNA polymerase used to synthesize viral DNA, capsomeres put into bacteria membrane

67

Assembly
(Bacteriophage)

capsomeres surround the viral DNA as it exits

68

Viral Relationships with Host Cells
(Latent/Lysogenic)

- No new viruses are produced by host cell
- Viral nucleic acid incorporated into host chromosome
- incorporated viral DNA called prophage in bacteria and provirus in animal cells.
- Host cell continues to divide and viral DNA is replicated with each new cell made

69

Lysogenic or Latent... what cell type and name

Lysogenic - Bacteria called prophage
Latent - Animal cell called provirus

70

most viral genes are NOT expressed in ______ state

lysogenic/latent
if genes are expressed the living host cell can produce new types of proteins- gives host new characteristics

71

Viral repressor proteins

can prevent production of the hosts excision proteins

72

excision proteins

found on host cell that cut viral DNA out of host chromosome

73

induction

excision proteins allowed to cut and release viral DNA, virus goes from lysogenic to productive/lytic

74

temperate virus

AKA lambda phage
a virus that can go from lysogenic to productive lytic

75

if the bacteriophage is inside it is in what phase

lysogenic phase

76

types of human viruses

virulent
latent
temperate

77

virulent viruses

always productive lytic, rapid, severe, destructive, cell death but not always organism death,
Ex. Influenza, mumps, polio

78

latent viruses

non-active, in dormant state inside cell, incorporate DNA into host chromosome
ex. HIV and herpes

79

Temperate viruses

can cause lysis or become latenet, environmental conditions may influence which state is present
ex. herpes

80

Acute infections

-cause disease symptoms for short periods of time
- body can develop life-long immunity
- viruses are productive
- extensive tissue damage and cell death, but is usually localized
- much of damage can be repaired after recovery
Ex. mumps, measles, influenza, cold virus

81

Persistent infections

- specific virus is present in host for long periods of time, life-long possible
- virus can be productive or latent depending on state of disease
- disease symptoms may not be apparent
- host become carrier of infective viruses

82

Late complications following acute infection
(persistent)

relapse can occur years after recovery from an acute infection
Ex. measles and subacute sclerosing panencephalitis (SSPE)

83

latent infections
(persistent)

similar infection occurs days to years after recovery from acute infection, viruses are not detected until disease onset.
- Herpes family viruses - shingles, chicken pox, genital herpes, cold sores
- Herpes simplex 1 - cold sores in mouth, move to neurons when latent, environmental triggers cause movement of virus back to mouth

84

Chronic infections
(persistant)

continuous production of low levels of viruses often in absence of disease symptoms
ex. Hep B and C - acute phase includes nausea and fever, virus can persist and slowly cause liver cirrhosis

85

Slow infections
(persistant)

number or viruses slowly increases over a long period of time
ex. HIV/AIDS

86

Cancer

abnormal condition of unregulated cell division

87

Tumor

mass of abnormally dividing cells

88

Benign tumor

remains within a localized region

89

Malignant tumor

cells migrate (metastasize) to other location

90

Regulatory genes

can regulate rate and frequency of cell division - without regulation cell may become cancerous

91

Two types of regulatory genes

Proto-oncogenes
Tumor-suppressor genes

92

proto-oncogenes

activate transcription, increase rate of cell division, cancer develops if gene is always on

93

tumor- suppressor genes

stop cell division, cancer develops if gene is turned off

94

Regulatory genes are altered by

Mutation - 80% of cancer (50% on tumor-suppressors, 30% on proto-oncogenes)
Viruses - 15% (or more) of all human cancers
last 5% is d/t genetic predispositon

95

Oncoviruses general info

-viruses that can transform host cell into a cancer cell
- latent - viral genes incorporated into host DNA
-induction can be caused by decreased immunity, stress, fever, UV exposure

96

Oncovirus definition

disrupt and permanently turn on proto-oncogenes

97

Retrovirus

RNA viruses use revese transcriptase to make double stranded DNA which is incorporated into host DNA, can modify host cell function including conversion to cancer cell

98

viroids

-single stranded, circular RNA, no capsid
- no proteins produced
- infect only plants
- mechanisms of disease production unknown
ex. potato spindle tuber

99

prions

- compose only of proteins
- affect CNS of humans and other animals
- Scrapie in sheep, Bovine spongegiform encephalophathy, and Creutzefeld-Jakob disease in humans
- very stable - resistant to heat and chemicals
Mechanisms unknown - normal host proteins destroyed, nerve cells destroyed.

100

Person infected with HIV virus by symptoms are not present

HIV infection

101

person infected with HIV and symptoms ARE present

HIV disease

102

Last stage of HIV disease, characterized by opportunistic infections

AIDS
Aquired Immunodeficiency Syndrome

103

Causative Agent of HIV

single stranded RNA virus, enveloped, retrovirus.
HIV-1 is more common in US than HIV-2