Viruses

Question 1

Reverse transcriptase catalyzes _____ production from a _____ template.

Answer 1

DNA; RNA,

Question 2

Compared with the number of antibiotics, the number of antiviral drugs is small because

Answer 2

viruses use host cell machinery to replicate.

Question 3

Which viral genome is likely to require an RNA-dependent RNA polymerase for transciption upon viral entry?

A. (+) sense single-stranded RNA
B. double-stranded DNA
C. single-stranded DNA
D. (–) sense single-stranded RNA

Answer 3

(–) sense single-stranded RNA does not appear like any of the genome intermediates of an animal cell. Consequently, (–) sense ssRNA viruses must encode a viral RNA-dependent RNA polymerase to transcribe the viral genome from a (–) RNA to a (+) mRNA. The viral mRNA can then be translated at ribosomes creating the remaining viral proteins needed for genome synthesis.

Question 4

The viral capsid is comprised of

Answer 4

The viral capsid is made of proteins.

Question 5

Which of the following statements is true?

Choose one:
A. Viruses limit evolution.
B. Since viruses are so small, they have a negligible impact on the environment.
C. Viruses may limit host population density.
D. Viruses do not jump from one species to another.

Answer 5

Viruses may limit host population density.

Question 6

In what ways do virions resemble living cells?

Answer 6

Some virions possess genes for tRNA.Their genomes can be larger than some cellular genomes.They possess genes that can direct their own replication. Just missing the ribosomes

Question 7

Phage lambda can undergo a lytic cycle or a lysogenic cycle where the phage DNA is integrated into the genome in the form of a prophage. In the case of lysogeny, what induces phage lambda to transition to the lytic cycle?

Answer 7

stress

Question 8

Which of the following is not an evolutionary adaptation by bacteria to escape viral infection?

Answer 8

A. CRISPR sequences
B. mutation of host surface proteins
C. histone acetylation
D. DNA methylation

Question 9

Which of the following conditions may lead to a switch from a lysogenic to a lytic life cycle?
A. A lack of glucose in the environment
B. High cellular ATP levels
C. An abundance of leucine in the environment
D. A polarized bacterial cell membrane

Answer 9

A lack of glucose

Question 10

Which viruses may enter cells via receptor-mediated endocytosis?

Answer 10

Animal viruses

Question 11

Compared with cells that are surrounded by a lipid membrane, viruses

Answer 11

Not all viruses contain a membrane envelope external to the capsid. Although enveloped viruses do contain a membrane external to the capsid, this membrane is derived from the host.

Question 12

What are the components common to all virions?

Answer 12

capsid, DNA or RNA genome

Question 13

CRISPR Bacterial Defense Mechanisms

Answer 13

protect from bacteriophage infection
- when viral DNA is inserted in the cell it is integrated at the CRISPR site (contain short repeats of DNA sequences alternating with short variable spacers corresponding to memory of foreign DNA)
- Cas9 protein binds with the spacer DNA forming surveillance sequence
upon re-exposure the CRISPR Cas9 protein will recognize the viral DNA and cut it
Cas9 proteins when seeing a new viral DNA will bind to the spacer and also integrate it into the CRISPR

Question 14

entry mechanism of animal viruses

Answer 14

• endocytosis of non-enveloped virus
• mb fusion of enveloped virus
• endocytosis of enveloped virus
  difference with bacterial viruses: entire virion enters the cell

Question 15

lytic cycle

Answer 15

attachment, virion enters, viral contents are released, Viral DNA or RNA isn’t integrated into genome new phages are assembled in the cytoplasm and leave in bacteriophages this causes cell lysis in animals the cell won’t die but will continue to make new virus

Question 16

lysogenic cycle

Answer 16

DNA or RNA of the virus is integrated in to the hose genome in stress the cell will enter the lytic cycle

Question 17

Genetic resistance defense

Answer 17

• altered receptor proteins, modification of the cell host recognition, can like obscure phage receptors or mask them

Question 18

Restriction Enzymes defense

Answer 18

bacteria digest viral genome using restriction enzymes

Question 19

viral tropism

Answer 19

• kinda like specificity
  ability to infect a particular tissue type within a host

Question 20

virulent vs latent

Answer 20

• always lyse and kill host after infection (lytic cycle always)
• temperate replicate their genome in tandem with host genome without killing host (can be lytic/ virulent or become so)

Question 21

Lysogen and lysogeny

Answer 21

geny: most viral genes not transcribed and viral genome is replicated and passed to daughter cells

gen: host cell harbours temperate virus can result in lysogenic conversion with new properties (can cause virulence in pathogens)

Question 22

retroviruses

Answer 22

use reverse transcriptase to copy their genomic sequence into DNA for insertion in the host membrane

Question 23

dna viruses

Answer 23

use host machinery
- can’t treat/make anti viral cause that would literally mean killing the host cell too usually

Question 24

rna viruses

Answer 24

use ran-dependent rna pol to transcribe mRNA

Question 25

latent

Answer 25

the virus is dormant within a cell, not producing more virus but still present in the body

Question 26

What is a virus and what’s it made of

Answer 26

noncellular particle that infects a host cell and directs it to produce it’s progeny, either DNA or RNA contained within a plasmid