Ch 5: Viruses

Question 1

What are viruses?

Answer 1

acellular infectious particles and obligate intracellular parasites

Question 2

Viruses are composed of biological molecules, e.g. nucleic acids, proteins, but not …

Answer 2

Cells

Question 3

Order from smallest to largest

Yeast, virus, bacteria

Answer 3

virus, bacteria, yeast

Question 4

What do all viruses have? What do only some viruses have?

Structure

Answer 4

All viruses have a NUCLEIC ACID GENOME
- genes for viral reproduction

PROTEIN CAPSID
- protective coat for transport of genes and attachment to
host cells

Some viruses have a LIPID ENVELOPE
- a phospholipid bilayer with spike proteins for attachment
to host cell

Question 5

What are the features of the viral capsid?

Answer 5

made of protein subunits called capsomers

may have capsid spikes for attachment to host cells
helical or polyhedral

Question 6

What are the features of the viral envelope?

Answer 6

stolen from host cell membrane by viral budding

phospholipid bilayer with viral “spike” glycoproteins

Question 7

What is the viral genome composed of?

Answer 7

DNA or RNA

Question 8

How are viruses classified by:

• Genome
• Capsid
• Envelope

Answer 8

• Genome: DNA or RNA
• Capsid: Helical or Polyhedral
• Envelope: Naked or Enveloped

Question 9

What is a virus that infects bacteria?

Answer 9

bacteriophage

Question 10

What are the steps of viral replication?

Answer 10

1. Adsorption
2. Penetration & Uncoating
3. Synthesis
4. Assembly
5. Release

Question 11

What is the step of the viral replication cycle, adsorption?

Answer 11

Attachment

tropism defines the host-cell specificity of a virus

Question 12

What are the methods of Penetration & Uncoating?

Answer 12

Endocytosis and Fusion

Question 13

What must be synthesized during viral replication?

Answer 13

NUCLEIC ACID SYNTHESIS
- make copies of viral genome

PROTEIN SYNTHESIS
 - make viral enzymes
 - make viral capsomers
 - make viral envelope spikes and insert in host 
    membrane

Question 14

How do bacteriophages introduce their DNA into host?

Answer 14

Injection

Question 15

What types of virus can enter the cell via endocytosis?

Answer 15

Enveloped virus and Naked Virus

Question 16

What is the tropism of HIV?

Answer 16

CD4 T Helper Cells

Question 17

How can Host Cells help w/ synthesis?

Answer 17

All cells have three enzymes and can perform…

CELLULAR REPRODUCTION
DNA → DNA x 2 (replication)
DNA polymerase

GENE EXPRESSION
DNA → RNA (transcription)
(DNA-dependent) RNA polymerase
mRNA → protein (translation)
ribosomes

Question 18

What is the Normal Flow of Genetic Information in Cells?

Answer 18

DNA →mRNA using RNA Polymerase
mRNA →Proteins using ribosome

DNA →DNA using DNA Polymerase

Question 19

What three things can a host cell do with DNA? (This is the flow of genetic information in cells)

Answer 19

• replication using DNA polymerase
• transcription using RNA Polymerase
• translation using Ribosomes

Question 20

How does a DNA virus use host cell enzymes?

Answer 20

COPYING VIRAL DNA (vDNA) GENOME
vDNA → vDNA x 2 using DNA polymerase (host)

EXPRESSION OF VIRAL GENES
vDNA → vRNA using DNA-dependent RNA polymerase (host)
vRNA → vProtein using ribosomes (host)

vProtein + vDNA = New Virion

Question 21

Walk through the types synthesis a DNA virus can perform.

Answer 21

vDNA

Question 22

How does a DNA virus use host cell enzymes?

Answer 22

COPYING VIRAL DNA (vDNA) GENOME
vDNA → vDNA x 2 using DNA polymerase (host)

EXPRESSION OF VIRAL GENES
vDNA → vRNA using DNA-dependent RNA polymerase (host)
vRNA → vProtein using ribosomes (host)

vProtein + vDNA + assembly = New DNA Virions

Question 23

How is the synthesis of RNA Viruses different that DNA Viruses?

Answer 23

RNA viruses require a viral enzyme, RNA Dependent RNA Polymerase, because host cells cannot make copies of RNA from a RNA template (no host enzyme)

Question 24

How is the synthesis of RNA Viruses different that DNA Viruses?

Answer 24

RNA viruses require a viral enzyme, RNA Dependent RNA Polymerase, because host cells cannot make copies of RNA from a RNA template (no host enzyme)

Question 25

How does an RNA Virus synthesize necessary components to replicate?

Answer 25

copying of viral RNA genome - vRNA → vRNA x 2 using RNA-dependent RNA polymerase (viral) expression of viral genes - vRNA → vProtein using ribosomes (host) vRNA + vProtein + assembly = new RNA Virions

Question 26

How is synthesis of RNA Retroviruses different from RNA viruses?

Answer 26

RNA retroviruses require a viral enzyme, Reverse Transcriptase, but the enzyme does not directly synthesize RNA; it makes DNA instead

Question 27

How does an RNA Retrovirus synthesize necessary components to replicate?

Answer 27

copying of viral NA genome into DNA - vRNA → vDNA using reverse transcriptase (viral) copying of viral DNA genome into RNA - vDNA → vRNA using DNA-dependent RNA polymerase (host) expression of viral genes - vRNA → vProtein using ribosomes (host) vRNA + vProtein + Assembly = New RNA Retrovirions

Question 28

What does it mean that RNA Viruses have "Low Fidelity"?

Answer 28

error prone = high mutation rate fidelity = ability to copy accurately every time

Question 29

How do some viruses incorporate their genomes into the host chromosome?

Answer 29

integration - HIV uses an enzyme called integrase to recombine the viral DNA copy into a host chromosome - latency = virus is dormant (host is unaware of infection) lysogeny - bacteriophage → prophage

Question 30

Which host enzyme is used by all viruses?

Answer 30

Ribosomes

Question 31

Which HIV enzyme promotes viral latency?

Answer 31

Integrase

Question 32

How are viruses released from host cells?

Answer 32

Naked viruses = lysis Enveloped viruses = budding (takes host membrane w/ it to form new envelope) - can insert spikes into host membrane before leaving

Question 33

What occurs during the step of viral replication called assembly?

Answer 33

capsomers coat copies of viral DNA or RNA to form capsid envelope spike proteins are inserted in the host membrane

Question 34

What enzyme does HIV require for assembly?

Answer 34

Protease processes proteins made by virus before assembly

Question 35

What are the enzymes necessary for HIV replication?

Answer 35

Reverse Transcriptase Integrase Protease These are targeted by HIV Antivirals

Question 36

You can't culture viruses by giving them nutritive cell media. How can you do it? How do you know it's working?

Answer 36

Have to "feed" viruses cells Grow viruses on other cells. You know it's working when you see viral plaques (cell lysis) on culture

Question 37

What do bacteriophages do?

Answer 37

viruses that infect bacteria. | - kill bacteria cells thorugh lysis

Question 38

What is phage therapy?

Answer 38

using bacteriophages to kill harmful bacteria

Question 39

What additional problems to cells, outside of killing them, can viruses cause?

Answer 39

Cytopathic effects like latent state (HSV)

Question 40

What are oncoviruses?

Answer 40

cancer causing viruses that transform cells HPV → genital warts → cervical cancer hepatitis virus → hepatitis → liver cancer

Question 41

How do we treat viral infections?

Answer 41

vaccines (against some viruses, e.g. MMR) antibiotics do not affect viruses limited antiviral agents (very specific to each virus) interferons

Question 42

Enveloped viruses are released from host cells by a process called:

Answer 42

Budding

Question 43

What type of virus is associated with cell transformation and cancer?

Answer 43

oncovirus

Question 44

What are prions?

Answer 44

non-viral infectious agents - defective (misfolded) neural proteins - reproduce w/o genes through conversion (misfold other neighboring proteins)

Question 45

Prions are infectious _______ proteins.

Answer 45

neural

Question 46

Prions do not have genes so they reproduce by a process called:

Answer 46

conversion

Question 47

Prions cause transmissible spongiform encephalopathies. How is it transmitted?

Answer 47

Cow w/ Bovine Spongiform Encephalopathy (mad cow disease) is slaughtered and the meat is eaten