Viruses

Question 1

All viruses have?

Answer 1

genome-DNA or RNA, double or single stranded
-capsid: protein coat

Question 2

What are capsomers?

Answer 2

Individual subunits that comprise the capsid
-self assemble into a capsid

Question 3

Some Viruses also have

Answer 3

envelope–> lipid bilayer derived from the host cell membrane during viral budding
-spikes–> viral proteins or glycoproteins in the envelope
-enzymes–> for replication or pathogenesis

Question 4

True or false: virtually all bacteriophages are naked

Answer 4

True

Question 5

What are the common viral shape

Answer 5

Icosahedron and helical

Question 6

How can viruses be classified

Answer 6

By host—> bacteriophage vs animal viruses
-By genome type—> single vs double stranded vs negative strand RNA
-enveloped vs naked

Question 7

What is the first step of Viral Replication

Answer 7

Adsorption–> ligands on viruses bind to receptors on host cells
-ligands may be on spikes or capsid proteins

Question 8

Can viruses infect any cell?

Answer 8

No they are highly specific

Question 9

What is the second step of virus replication?

Answer 9

Penetration—> release of the nucleic acid from the capsid
-phage usually inject genome into bacterial cell, leaving capsid outside

Question 10

During penetration how do animal viruses enter the cell?

Answer 10

Enter cells by fusion or endocytosis

Question 11

What is the third step of Virus replication?

Answer 11

Synthesis

-dsDNA and ssDNA viruses–> can use host to make new viral genomes

-dsRNA and ssRNA viruses—> need RNA replicase enzyme ro make new viral genomes. RNA replicase enzyme must be carried in the virus in a -strand Virus RNA

-retrovirus—> strand ssRNA genomes uses a dsDNA intermediate
-carries the enzymes reverse transcriptase and integrate
-DNA intermediate integrates into host genome

Question 12

What are early proteins?

Answer 12

hijack the cell; force the synthesis of new viral genomes and viral coats
-example: viral sigma factor

Question 13

What are late proteins?

Answer 13

Viral proteins that are part of the mature virion

Question 14

What is the fourth step of virus replication?

Answer 14

Assembly–> capsids self assemble; genomes packaged inside
-phage assemble in the cytoplasm
-animal viruses may assemble in the nucleus or cytoplasm depending on the virus

Question 15

What is the final step of virus replication?

Answer 15

Release—> some enveloped viruses are released by budding from the plasma membrane which doesn’t necessarily kill the host
-some types of viruses instead gain their envelope by budding into the ER, ERGIC, or Golgi during assembly nd are released by exocytosis

Question 16

Virulent phage

Answer 16

can only use lytic replication

Question 17

Temperate phage

Answer 17

Can use both lytic an lysogenic replication

Question 18

Lysogen

Answer 18

Bacterial cell containing a prophage

Question 19

Prophage

Answer 19

The phage genome integrated into the host cell genome

Question 20

What is the lambda repressor important for?

Answer 20

Is essential for maintaining lysogeny
-is a phage encoded protein that represses the transcription of most phage genes except itself

Question 21

What is the role of Hfl protease

Answer 21

Can degrade the lambda repressor
High glucose–> low cAMP–> high Hfl
-high glucose lead to increased degradation of lambda repressor by Hfl which favors the lytic cycle

Question 22

Replication of temperate phage

Answer 22

integration

-circularization(so not degraded)
-site specific recombination(not homologous recombination) between attP and attB catalyzed by phage encoded integrase

Maintenance of lysogeny
-the lambda repressor id essential for maintaining lysogeny
-represses the transcription of most phage genes

Excision:
prophage induction occurs due to environmental conditions that are harmful to bacteria

Question 23

How can coronavirus enter the cell?

Answer 23

-can enter cells via fusion with the plasma membrane or through endocytosis
-either way spikes of SARS-coV2 binds to ACE2

Question 24

What are prions?

Answer 24

an infectious proteinaceous particle
-thought to be incorrectly folded proteins that induce other proteins to be misfodled and aggregate

Question 25

What are characteristics of prions?

Answer 25

1. resistant to inactivation by heating to 90 C. A temperature that will inactivate viruses
2. not sensitive to radiation which ordinarily damages virus genome
3. not destroyed by enzymes that digest RNA or DNA
4. sensitive to protein denaturing agent

Question 26

What is the harmless form of prions?

Answer 26

PrP A which is rich in alpha helices

Question 27

What is the harmful form of prions

Answer 27

The beta sheet form

Question 28

Describe the 4 different outcomes of infection of an animal cell by an animal virus. How do these differ from the outcomes of infection of a bacterial cell by phage?

Answer 28

Latency is a characteristic of the herpesviruses, which include Herpes simple viruses, chickenpox virus (varicella), and the virus that causes mononucleosis (Epstein-Barr)
-Latent infection: virus present but not causing harm to cell; later emerges in lytic infection –> long term chronic infection

–the viral genome becomes an episome
–the expression of genes involved in lytic replication is suppressed
–reactivation can occur due to stress or immunosuppression

Question 29

Describe the steps in the replication of the 2009 A(H1N1) influenza virus. What are the roles of the HA, NA, and PB proteins in the spread of the virus? Why is this virus considered a “quadruple reassortant”?

Answer 29

Roles of proteins in virus
-HA (hemagglutinin): binds to sialic acids on cells of respiratory tract; also plays an important role during virus uncoating in the endosome
-NA (neuraminidase): cleaves the sialic acid residues; role in release/shedding of virion during budding
-PB1 (viral RNA polymerase/RNA replicase): RNA replicase is only present in the virus’s virion; it is an RNA dependent RNA Polymerase that uses the RNA as a template to make DNA.

-the 2009 A(H1N1) is considered a Quadruple Reassortment b/c it has 4 distinct sources of the gene segments in the virus
–Segments: Avianlike, Humanlike, Swinelike, & Eurasian like

Question 30

Which viruses can rely on the host cell to supply the enzyme that replicates the viral genome? Which viruses cannot rely on the host cell to supply the enzyme that replicates the viral genome? Why?

Answer 30

x-double stranded DNA and single stranded DNA viruses can use the host enzyme s to make new viral genomes b/c the DNA polymerase can use the DNA template to make more DNA

-double stranded RNA and single stranded RNA viruses need RNA replicase enzyme (RNA dependent RNA polymerase) to make new viral genomes. RNA replicase enzyme MUST be carried in the virion in a negative (-) strand RNA virus

Question 31

Virus vs bacteria

Answer 31

Viruses vs. Bacteria
➢ Bacteria:
-living organism; unicellular; one cell
-larger (1000 nm)
-fission: a form of asexual reproduction
-cell wall: peptidoglycan or lipopolysaccharide
-has ribosomes
-DNA and RNA floating freely in cytoplasm
-“localized” infection
-usually treated w/ antibiotics

➢Viruses:
-not living; no cells
-smaller (20-400 nm)
-reproduction: invades a host cell, taking control and copies the viral DNA/RNA, then destroys the host cell and releases new viruses
-No cell wall; has protein coat (capsid)
-No ribosomes
-DNA or RNA enclosed inside a coat of protein
-“systemic” infection
-antibiotics will not effect the disease

Question 32

Lysogenic conversion

Answer 32

The prophage alters the genome of the bacterium conferring new properties

Question 33

what did the the Luria Delbruick fluctuation test show

Answer 33

That mutations occur spontaneously