Viruses

Question 1

What is the structure of a virus?

Answer 1

Nucleic acid encased in a protein coat

Question 2

Where does a virus replicate?

Answer 2

In the host cell only

Question 3

What are the 4 steps of viral replication in a host cell?

Answer 3

Replication of viral genome, transcription, translation, reassembly

Question 4

What does it mean when a virus is an inert particle?

Answer 4

No metabolism, replication, or motility

Question 5

What is the protein coat of a virus called?

Answer 5

Capsid, comprised of subunits called capsomeres and carries enzymes

Question 6

What is the difference between an enveloped and non-enveloped virus?

Answer 6

enveloped viruses have a lipid bilayer, making them less resistant to disinfectants

Question 7

Where is the matrix protein located?

Answer 7

Between the envelope and nucleocapsid

Question 8

What are the different types of viral genome?

Answer 8

DNA or RNA, linear or circular, double or single-stranded

Question 9

How do viruses attach to the host cell?

Answer 9

Protein components, tail fibers in phages, spikes in some animal viruses

Question 10

What are the 4 different types of viruses?

Answer 10

helical, icosahedral, complex, and spherical

Question 11

What are the 3 types of bacteriophages(viruses that infect bacteria)?

Answer 11

Lytic phages, temperate phages, filamentous phages

Question 12

What is the characteristic of a lytic phage?

Answer 12

When they exit the host cell, the cell undergoes lysis(it bursts)

Question 13

What are the 5 steps of the lytic cycle?

Answer 13

attachment, entry of phage dna and degradation of host dna, synthesis of viral genomes/proteins, self-assembly of proteins, release

Question 14

What is the burst size of a bacterial cell?

Answer 14

The amount of phage particles released upon lysis

Question 15

What are the steps of the lysogenic cycle?

Answer 15

integration of phage DNA, cell division, formation of daughter cell with prophage

Question 16

What are the bacterial defenses against phages?

Answer 16

preventing phage attachment, restriction enzymes, crispr/cas

Question 17

How do bacteria prevent phage attachment?

Answer 17

Absence of receptors on surface, or alteration of receptors so that phages cannot bind

Question 18

How do restriction enzymes work?

Answer 18

They prevent phages from replicating genome inside the bacterial cell by recognizing and cutting short nucleotide sequences into small, non-infectious fragments. Can also occur by methylating host DNA to distinguish from phage DNA

Question 19

How does the CRISPR/Cas system work?

Answer 19

Infection by phage triggers expression of CRISPR(clustered regularly interspaced short palindromic repeats), from phages that previously infected the cell. Then the RNA transcript is processed into short strands, and each strand binds to a CAS protein forming a complex. Complementary RNA binds to phage dna, and then CAS cuts the segment. the DNA from the phage is now degraded.

Question 20

What are the key characteristics of animal viruses?

Answer 20

DNA or RNA based, single or double stranded, enveloped or non enveloped, hosts are infected

Question 21

What is the central dogma of biology?

Answer 21

DNA to RNA to proteins

Question 22

What are some aspects of synthesis of viral genetic material?

Answer 22

Expression of viral genes to provide structural and catalytic genes(capsid, replication enzyme)
synthesis of multiple copies of genome

Question 23

What are the three viral replication strategies?

Answer 23

DNA viruses, RNA viruses, reverse transcribing viruses

Question 24

What is the difference between sense and antisense strands?

Answer 24

the template strand is antisense and noncoding, and the nontemplate strand is sense and coding

Question 25

Why is antisense RNA present in a cell?

Answer 25

inhibits translation machinery by base pairing with sense RNA and activating RNAse H to develop novel transgenic

Question 26

How do DNA viruses replicate?

Answer 26

ds dna becomes rna and then protein; for ss rna the complement is synthesized and the same thing happens. uses dna and rna-dependent dna polymerase

Question 27

How do RNA viruses replicate?

Answer 27

replicate in cytoplasm, require virally encoded RNA polymerase(replicase), which allows genetic drift because it lacks proofreading. ss sense RNA is used as MRNA, anything else is converted by synthesizing complement

Question 28

What is the replicative cycle of an enveloped RNA virus?

Answer 28

glycoproteins on viral membrane bind to host cell, capsid and viral genome enter cell and enzymes release the genome, viral rna polymerase synthesizes complement of viral genome, new copies of genome are synthesized, mrna(complementary) is translated into protein, vesicles transport protein to virus and the capsid assembles. then the virus exits with a shit ton of glycoproteins on the membrane.

Question 29

How do new viruses emerge?

Answer 29

mutation of existing viruses, spread due to international travel, spread of existing viruses from other animals

Question 30

How do reverse transcribing viruses replicate?

Answer 30

encode reverse transcriptase(make DNA from RNA)(retroviruses have ss + rna), then the complementary strand is synthesized and the dsdna is integrated into the host cell’s chromosome.

Question 31

What are the 3 genes all reverse transcribing viruses have?

Answer 31

gag(viral protein coat), pol(reverse transcriptase and integration of DNA), env(glycoproteins on viral membrane)

Question 32

What is the replicative cycle of HIV?

Answer 32

1. envelope glycoproteins enable the virus to bind receptors on white blood cells
2. virus fuses w host cells plasma membrane
3. capsid is removed, releasing rna, viral proteins, adn reverse transcriptase
   4.rt synthesizes dna
4. rt catalyzes complementary strand synthesis
5. dna is integrated into host cell dna
6. proviral genes are transcribed onto rna
7. capsid and rt are made in cytosol, envelope glycoproteins made in er
8. capsid and glycoproteins assemble around the viral molecule

Question 33

What are prions?

Answer 33

proteinaceous infectious agents, no nucleic acid
causes slow fatal diseases like mad cow