Lecture 19: Viruses

Front 1

What size are poxviruses?

Back 1

250 nm

about the same size as chlamydiae and mycoplasmas in size (poxviruses are about as big as these smallest bacteria)

Front 2

What size are parvoviruses?

Back 2

20 nm

about the same diameter as DNA

Front 3

100 nm is equal to how many um?

Back 3

0.100

100nm=0.100um

Front 4

Viruses can't reproduce on its own. They must go in humans or some other host. In other words, viruses are ___

Back 4

obligate intracellular parasites

Front 5

Who discovered viruses in the early 1800's by looking at plant sap of tobacco?

Back 5

Dmitri Ivanowsky

Front 6

What are the 3 different shapes viruses come in?

Back 6

Helical
Icosahedral
Complex

Front 7

What viruses fit under the category "helical viruses"?

Back 7

Tobacco mosaic virus
Rabies virus
Measles virus

Front 8

What viruses fit under the category "Icosahedral viruses"?

Back 8

herpes simplex virus
polio virus
parvovirus

Front 9

What viruses fit under the category "complex viruses"?

Back 9

Bacteriophages
smallpox virus
influenza virus

Front 10

All viruses consist of two basic components: a core of nucleic acid called the _____ and a surrounding coat of protein known as the ___

Back 10

genome
capsid

Front 11

The genome contains ______; and the nucleic acid occurs in ______

Back 11

either DNA or RNA, but not both

double-stranded or single-stranded form
ssDNA or ssRNA
dsDNA or dsRNA

Front 12

The capsid is a surrounding ______ coat and it protects the genome

Back 12

protein

Front 13

The capsid is subdivided into individual protein subunits called _____

Back 13

capsomeres

The number of capsomeres is characteristic for a particular virus.

Front 14

What are three things are important about the capsid?

Back 14

1) characteristic # of capsomeres
2) gives shape to virus
3) protects genome

Front 15

The capsid plus the genome is called the ____

Back 15

nucleocapsid

Front 16

Many viruses are surrounded by a _____ and _____ membrane known as an envelope

Back 16

lipid and protein

Front 17

Many viruses are surrounded by a lipid and protein membrane known as an ____

Back 17

envelope

Front 18

In some viruses, the envelope contains functional projections known as ____

Back 18

spikes

Front 19

Spikes contain ____ for attachment

Back 19

enzymes

Front 20

No envelope, no ___

Back 20

infect

Front 21

A completely assembled and infectious virus outside its host cell is known as a ___

Back 21

virion

Front 22

A T4 bacteriophage is a complex virion with a head and a tail, but no ___

Back 22

envelope

Front 23

The best known process of replication in E. coli is that carried on by bacteriophages of the T-even group (T for "type"). Bacteriophages ___, ___, and ___ are in this group

Back 23

T2, T4, T6

Front 24

burst size

Back 24

How many new phages are made at the conclusion of the replication process. (50 to 200 new phages emerge from the host cell)

Front 25

bacteriophage

Back 25

virus

(bacteriophage = virus)

Front 26

What are the five stages of bacteriophage replication?

Back 26

1) Attachment
2) Penetration
3) Biosynthesis
4) Maturation
5) Release

Front 27

What happens during attachment?

Back 27

The bacteriophage's tail or viral capsid attaches to its host cell (bacterium) at a complementary receptor site.

Front 28

What happens during penetration?

Back 28

The capsid remains outside the cell, while the viral genome enters the cell's cytoplasm.

(viral DNA injected intracellularly, capsid extracellular)

Front 29

What happens during biosynthesis?

Back 29

The viral genome encodes proteins for the synthesis of new viral parts. The cell's nucleic acid degrades

Front 30

What happens during maturation?

Back 30

New viruses are assembled from the newly synthesized capsids and genomes, usually in a step-by-step process.

Front 31

What happens during release?

Back 31

New viruses are released from the host cell to infect adjacent cells and begin a new cycle of replication.

(host destroyed, new viruses released)

Front 32

burst time

Back 32

The time that passes from phage attachment to the release of new viruses.

Front 33

The method of replication displayed by T-even phages is similar to that in animal viruses, but with some notable exceptions. One example is the attachment phase. Like bacteriophages, animal viruses have attachment sites, but the receptor sites exist on the host _____ rather than the ____.

Back 33

plasma membrane
cell wall

Front 34

animal viruses have no tails, so the attachment sites often are the _____ distributed over the surface of the capsid or envelope

Back 34

spikes

Front 35

Penetration of T-even phages and animal viruses are also different. Phages inject their DNA into the host cell cytoplasm, but animal viruses usually are taken in toto (become one w/host cell) into the cytoplasm. What are the two methods of penetration?

Back 35

1) spikes interact with host cell membrane
2) entire enveloped virus endocytosed

Front 36

What happens in the method where spikes interact with the host cell membrane?

Back 36

envolpe fuses with host cell membrane

Front 37

What happens in the method where the entire enveloped virus is endocytosed?

Back 37

envelope is removed in cytoplasm of host cell

Front 38

The final steps of viral replication may include the acquisition of an envelope. In this step, envelope proteins are synthesized and incorporated into a nuclear or cytoplasmic membrane, or the plasma membrane. Then, the virus pushes through the membrane, forcing a portion of the membrane ahead of it and around it, resulting in an envelope. This process, called ____, need not necessariy kill the cell during the virus's exit. The same cannot be said for unenveloped viruses, however. They leave the cell when the cell membrane ruptures, a process that generally leads to cell death.

Back 38

budding

Front 39

viruses with envelopes bud from the cell without ____

Back 39

lysing host

Front 40

Non-enveloped viruses rupture the ____

Back 40

host cell membrane

Front 41

____ and ____ DNA genomes are made in the host nucleus

Back 41

Adenovirus and herpesvirus

Front 42

Some DNA viruses employ a division of labor: DNA genomes are synthesized in the host cell nucleus, and capsid proteins are produced in the ____. The proteins then migrate to the nucleus and join with the nucleic acid molecules for assembly of nucleocapsid. The envelope comes from ____

Back 42

cytoplasm
nuclear membrane

Front 43

Describe the process of the replication of a DNA Animal Virus that replicates in the host nucleus

Back 43

1) The host cell membrane fuses with the viral envelope, thereby permitting entry of the nucleocapsid to the cytoplasm

2) The viral capsid is uncoated by cell enqymes, and the DNA of the viral genome enters the cell's nucleus

3) New viral DNA is synthesized in the nucleus resulting in new genomes. Transcription produces mRNAs that are translated on cytoplasmic ribosomes

4) Capsid proteins are synthesized in the cell's cytoplasm

5) Capsid proteins enter the nucleus and combine with viral genomes to form new nucleocapsids

6) The viruses bud through the nuclear envelope, endomembranes (for chickenpox), or plasma membrane to acquire their envelope before the mature virions are released

Front 44

While adenoviruses and herpesviruses DNA genomes are made in the host nucleus, Other DNA viruses like ____ replicate in the host cytoplasm

Back 44

poxviruses

Front 45

The RNA can act as a messenger RNA molecule and immediately begin supplying the codes for protein synthesis. Such a virus is said to have "sense"; it is called a ______, or ____

Back 45

positive-stranded RNA virus

sense virus

*Genome acts as mRNA, used as template for translation of viral proteins
*get in human host cell, genome is ready made for causing disease

Front 46

Give an example of a + stranded RNA virus

Back 46

polio virus

Front 47

In some RNA viruses, however, the RNA is used as template to synthesize a complementary strand of RNA. The latter then is used as a messenger RNA molecule for protein synthesis. The original RNA strand is said to have "antisense," and the virus is therefore an _______ or a ______. Usually the enzyme RNA polymerase is present in the virus to synthesize the complementary strand.

Back 47

antisense virus
negative-stranded RNA virus

*Viral-encoded RNA polymerase makes complementary strand of RNA, used as template for translation of viral proteins.

Front 48

_______ makes complementary strand of RNA, used as template for translation of viral proteins.

Back 48

Viral-encoded RNA polymerase

Front 49

Give an example of a negative stranded (antisense) RNA virus

Back 49

measles virus

Front 50

Retroviruses carry their own enzyme, called ____

Back 50

reverse transcriptase

Front 51

Give an example of two Retroviruses

Back 51

leukemia
HIV

Front 52

viral-encoded reverse transcriptase makes _____ from ____

Back 52

ssDNA from RNA genome

RNA genome ---> reverse transcriptase ----> ssDNA

Front 53

In the formation of a Provirus, a complementary strand is made to yield ____.

Back 53

dsDNA

*THe virus penetrates the host cell. After uncoating, reverse transcription of the viral genome catalyzes the synthesis of double-stranded DNA.

Front 54

Complementary strand made to yield dsDNA. Viral DNA integrates into host cell genome, becomes _____

Back 54

provirus

*The new DNA is transported into the host cell's nucleus and integrated into the nuclear DNA as a provirus.

Front 55

Viral DNA will incorporate into host cell genome, so can't figure out if it is foreign or not. THerefore, Provirus is immune to ______.

Back 55

host cell antibodies. Antibodies cannot penetrate cells

Front 56

A virus is replicated whenever ____

Back 56

chromosome is copied

Front 57

In the replication cycles, infection need not result in new viral particles or cell lysis. Rather, the virus may integrate its DNA or its RNA (via DNA) into a chromosome of the cell. When bacteriophages are involved, the phage DNA in the lysogenic state in a bacterial cell is called a prophage; when an animal virus (such as a retrovirus) is involved, the viral DNA is known as a ___

Back 57

provirus

Front 58

What are the 3 hypotheses for the origins of viruses?

Back 58

1) Regressive Evolution Hypothesis
2) Cellular Origins Hypothesis
3) Independent Entities Hypothesis

Front 59

Regressive Evolution Hypothesis

Back 59

Viruses are degenerate life-forms; that is, they are derived from intracellular parasites that have lost many functions that other organisms possess and have retained only those genes essential for their parasitic way of life.

Front 60

Cellular origins hypothesis

Back 60

Viruses are derived from subcellular components and figured out how to replicate autonomously in host cells

Front 61

Independent Entities Hypothesis

Back 61

Viruses coevolved with cellular organisms from the self-replicating molecules beilieved to have existed in the primitive prebiotic earth

Front 62

Why aren't antibiotics effective against viral infections?

Back 62

1) viruses use host enzymes and machinery
2) Viruses have no cell walls

Front 63

Viruses rely almost exclusively on the _____ for their replication

Back 63

host cell's metabolic machinery

Front 64

Because viruses rely almost exclusively on the host cell's metabolic machinery for their replication, it is difficult to ____

Back 64

find targets of selective toxicity

Front 65

What are two things most antiviral drugs do?

Back 65

1) Disrupt critical stages of the virus life cycle

2) prevent synthesis of virus-specific nucleic acids

Front 66

Most antiviral drugs disrupt critical stages of the virus life cycle. _____ blocks uncoating of influenza virus

Back 66

amantadine

Front 67

What does amantadine do?

Back 67

amantadine blocks uncoating of influenza virus. It stops the influenza virus at a step in its life cycle. It needs to uncoat, but can't now!

Front 68

Amantidine blocks the uncoating of the influenza virus. It prevents/reduces the ____

Back 68

severity and duration of disease

Front 69

Most antiviral drugs prevent synthesis of virus-specific nucleic acids. _____ stops herpes infections by disrupting activity of virus-specific nucleic acid synthesis enzymes

Back 69

vidarabine

Front 70

What does vidarabine do?

Back 70

Vidarabine stops herpes infections by disrupting activity of virus-specific nucleic acid synthesis enzymes

Front 71

What are the four major classes of antiviral drugs?

Back 71

base analogs
reverse transcriptase inhibitors
neuraminidase inhibitors
protease inhibitors

Front 72

base analogs look like _____

Back 72

nucleotides

Front 73

Once base analogs are incorporated, it stops the _____

Back 73

synthesis of nucleic acids

Front 74

What base analog is used to treat genital herpes and chickenpox?

Back 74

acyclovir

Front 75

What base analog is used to treat HIV?

Back 75

Azidothymidine (AZT)

Front 76

What do reverse transcriptase inhibitors do?

Back 76

binds and inhibits reverse transcriptase

No reverse transcriptase in our cells, so inhibitors inhibits reverse transcriptase. only targets retroviruses

Front 77

What two reverse transcriptase inhibitors blocks replication of retroviruses?

Back 77

Nevirapine
delavirdine

Front 78

What do Neuraminidase inhibitors do?

Back 78

prevents attachment of influenza virus

Neuraminidase is an enzyme in the spike of the influenza virus. It helps the virus infect cells and, after replication, helps the viruses spread to other cells. The neuraminidase inhibitor drug zanamivir blocks the action of neuraminidase, preventing release of new virions--and thereby limiting disease spread in the body.

Front 79

Name a neuraminidase inhbitor

Back 79

zanamivir

Front 80

What do protease inhibitors do?

Back 80

These drugs react with protease, the enzyme that trims viral proteins down to working size for the construction of the capsid.

*protease function required for HIV capsid construction

Front 81

Guve three examples of protease inhibitors

Back 81

saquinivir
indinavir
ritonavir

Front 82

saquinivir, indinavir, and ritonavir looks like _______; therefore, they act as decoys

Back 82

the peptide bond that is normally attacked by protease

protease (cuts up proteins) ---> protease inhibitors (decoys) --> won't attack capsid protein now. just attack protease inhibitors

Front 83

What are interferons?

Back 83

20 proteins produced by body cells in response to viral invasion. They provide protection against viruses.

Front 84

Interferons stimulates the production of ______ that interfere with viral reproduction in neighboring cells

Back 84

antiviral proteins

Front 85

Describe the production and activity of interferon

Back 85

A) Viral RNA stimulates the host to synthesize interferon while also directing replication of new viruses

B) Interferon is synthesized and released from the cell

C) viruses are released following replication

D) Interferon binds to a neighboring cell

E) Interferon induces the cell to express the genes for antiviral proteins

F) Antiviral proteins (AVPs) are synthesized

G) The antiviral proteins block viral protein synthesis and thus interfere with viral replication

Front 86

Interferons are normally made by viruses. They can synthesize outside the body and work as ____

Back 86

chemotherapeutic agents

Front 87

What are prions?

Back 87

proteinaceous infectious particles

Front 88

What do prions cause?

Back 88

kuru (cannibalism)

mad cow disease (bovine spongiform encephalopathy)

Front 89

what is mad cow disease also known as?

Back 89

bovine spongiform encephalopathy

Front 90

What is the incubation period for prions?

Back 90

8-12 yrs

Front 91

Prions cause brain cells to develop ____

Back 91

spongiform encephalopathies

Front 92

Who studied the disease in sheep called scrapie?

Back 92

Stanley Prusiner.
He found a protein in the brain. It wasn't a virus. How could the protein cause disease? PRION!

Front 93

What don't prions have?

Back 93

no nucleic acid

Front 94

How are prions killed?

Back 94

proteases

*no nucleic acid, killed by proteases

Front 95

What can prions survive?

Back 95

heat, radiation, and chemicals that viruses cannot

Front 96

What is the symbol for the normal prion protein?

Back 96

PrPc

Front 97

What does PrPc do?

Back 97

It binds copper in the brain. Copper is required for superoxide dismutase which protects cells from oxygen free radicals

Front 98

Copper is required for ______ which protects cells from oxygen free radicals

Back 98

superoxide dismutase

Front 99

What is the symbol for the normal prion in the wrong conformation?

Back 99

PrPsc

Front 100

PrPSC. Ingested misshapen prion may travel to brain and do what?

Back 100

change normal prion proteins- cause disease

Front 101

What is needed for diagnosis and confirmation?

Back 101

brain biopsy

Front 102

The nerve cell, ____, wants to get the bad prion (PrPsc). It clumps it together. It can't destroy the prions. prions kill the nerve cell and leaves a space. get spongiform.

Back 102

lysosome

Front 103

The influenza virion belongs to the _____ family of viruses.

Back 103

Orthomyxoviridae

Front 104

The influenza virus is composed of eight _____, each would helically and associated with protein to form a nucleocapsid

Back 104

(-)ssRNA

*normally single genome. now in influenza. eight different genomes; therefore, a segmented genome. each genome is covered in proteins

Front 105

_____ surrounds each helix

Back 105

capsid

Front 106

______ surrounds the core of segments

Back 106

matrix protein

Front 107

______ surrounds matrix protein

Back 107

envelope

Front 108

Projecting from the envelope is a series of spikes that contain ______

Back 108

glycoprotein

Front 109

H spike stands for ____

Back 109

hemaglutinin