Deck 27: Viruses of Algae and Mimivirus

Question 1

There is a 1788bp sequence in the middle of the genome of PBCV-1,a phycodnavirus,that does not code for any proteins.What is the function of this region of the genome?

A)It contains 11 tRNA genes.
B)It is the origin of DNA replication.
C)It is an enhancer involved in regulating gene expression.
D)It is a packaging sequence involved in insertion of the viral genome into the capsid.
E)None of the above.

Answer 1

A

Question 2

What does mimivirus have in common with poxviruses?

A)They both have genomes of over 1 million base-pairs.
B)Their virions are both large enough to be easily seen with a light microscope.
C)They both have a brick shaped virion.
D)They both replicate in the cytoplasm of their host cell.
E)The both cause severe and deadly diseases in humans.

Answer 2

D

Question 3

The virion of the chlorovirus PBCV-1 has a spike located at one of the 12 pentameric vertices.Which of the following describes the function of this spike?

A)It represents the point in the capsid where the DNA is packaged into the virion.
B)It attaches to the host cell and initiates entry of the virion.
C)It contains enzymes at its outer tip that degrade the cell wall of the host.
D)It is an important intermediate in the assembly of the capsid.
E)It is the point of attachment between the internal lipid envelope and the outer capsid.

Answer 3

B

Question 4

What does the name "mimivirus" refer to?

A)The name of the person who discovered the virus.
B)A shortened version of "microbe-mimicking" virus.
C)Abbreviation of "mega informational monstrous infectious" virus
D)The name of the host species that the virus infects.
E)The name of the location where the virus was discovered.

Question 5

The coccolithoviruses encode enzymes that produce the sphingolipid ceramide.What is the proposed function of this lipid in infected cells?

A)It enhances the production of cellular membranes,which the virus requires for replication.
B)It modifies cellular membranes,which enhances binding and entry of virions.
C)It activates apoptosis,causing host cells to lyse and release virus particles.
D)It inhibits apoptosis,allowing host cells to stay alive longer.
E)It induces signaling pathways in the host cell that increase viral replication.

Question 6

Which of the following represents the group of organisms infected by phycodnaviruses?

A)Insects.
B)Plants.
C)Prokaryotic cyanobacteria.
D)Eukaryotic algae.
E)Amoeba.

Question 7

Which of the following characteristics distinguishes the coccolithoviruses from the chloroviruses,which are both member of the phycodnavirus family?

A)Only the coccolithoviruses have a virion with an internal envelope.
B)Only the coccolithoviruses are predicted to encode over 300 proteins.
C)Only the coccolithoviruses replicate entirely in the nucleus of the host cell.
D)Only the coccolithoviruses encode their own DNA polymerase.
E)Only the coccolithoviruses encode their own RNA polymerase.

Question 8

Upon infection with a coccolithovirus,the microalgal host cell may switch from the usual diploid life stage to a haploid cell.Which of the following describes the advantage this has for the host cell?

A)The haploid cell can not replicate the viral genome,so no new viruses are produced.
B)The haploid cell produces a barrier that prevents virus particles from entering.
C)The haploid cell can swim away from virus infested waters.
D)The haploid cell can fuse with other haploid cells,producing virus resistant strains.
E)The haploid cell does not produce the host cell receptor for virus entry.

Question 9

The primary capsid protein of the phycodnavirus PBCV-1,Vp54,is glycosylated.Which of the following describes how the viral protein is thought to acquire its sugar residues?

A)The sugars are added to the protein inside the lumen of the rough ER.
B)Cellular enzymes in the cytoplasm add the sugars to the capsid protein.
C)Viral enzymes add the sugars directly to the capsid protein.
D)The sugars are added to the protein in the Golgi of the host cell.
E)The sugars are added by viral enzymes after release of the virion from the host cell.

Question 10

All of the following virus families are members of the superfamily of Nucleo-Cytoplasmic Large DNA viruses EXCEPT...

A)Phycodnaviridae
B)Adenoviridae
C)Mimiviridae
D)Poxviridae
E)Asfarviridae

Question 11

Which of the following describes the primary distinguishing feature of the prasinoviruses?

A)They have the largest virions of any known virus.
B)They have the largest genome of any known virus.
C)They produce more virions per round of replication than any known virus.
D)They infect the smallest free-living eukaryotic cell.
E)They only replicate inside the nucleus of their host cell.

Question 12

Which of the following mechanisms is thought to have caused the mimivirus genome to become so large?

A)Insertion of the genome of another virus into the mimivirus genome.
B)The insertion of a large transposon into the genome.
C)Acquisition of new genes from the genome of its host.
D)Acquisition of large segments of non-coding DNA.
E)Self-duplication of regions of the genome.

Question 13

While mimiviruses encode more of the components of the protein synthesis machinery than other viruses,they still do not produce which of the following?

A)Aminoacyl-tRNA synthetases.
B)Ribosomes
C)tRNA methyltransferases
D)tRNAs
E)Translation initiation factors

Question 14

Which of the following may explain why mimiviruses encode a high number of DNA repair enzymes?

A)Their host produces a large number of nucleases.
B)The method used to replicate the viral genome introduces many mutations.
C)During long periods between infections,they are exposed to UV light.
D)During entry,the genome would be exposed to oxidizing conditions.
E)Both "c" and "d" are correct.

Question 15

All of the following characteristics are common to the virions of all of the phycodnaviruses EXCEPT:

A)They have a core which contains the double-stranded DNA genome.
B)The DNA containing core is surrounded a lipid bilayer.
C)The internal lipid membrane is surrounded by an icosahedral capsid.
D)The presence of an outer membrane acquired by budding from the host cell.
E)All of the above are found in the virions of all phycodnaviruses.

Question 16

One of the reasons why the phcyodnaviruses are so diverse is that their hosts are ancient and equally as diverse.

Question 17

Which of the following statements about the phaeoviruses,members of the phycodnavirus family,is FALSE?

A)They infect the multicellular brown algae.
B)They integrate their viral genome into the host cell genome.
C)They are found in both marine and freshwater environments.
D)They only infect the free-swimming gametes of their host.
E)Productive replication of the virus makes the host sterile.

Question 18

Like most other eukaryotic viruses,the entire virion of the chlorovirus PBCV-1,a phycodnavirus,enters the host cell and releases the viral genome into the nucleus.

Question 19

Which of the following statements describes a characteristic of the late genes of the phycodnavirus PBCV-1?

A)They are only transcribed after DNA synthesis has begun.
B)They are transcribed by the host cell RNA polymerase.
C)They encode structural proteins.
D)They were detected by hybridizing RNA to probes of each viral gene.
E)All of the above are characteristics of late genes.

Question 20

The prasinovirus which infects the green alga Ostreococcus only produces 6-15 virus particles per infectious cycle.Which of the following explains why the burst size is so small?

A)The host cell is not big enough to hold any more virus particles without lysing.
B)The host cell has a hard outer coating that makes it difficult for virus particles to leave the cell.
C)The host cell dies too quickly to allow more virus particles to be produced.
D)The cell does not contain enough raw materials to allow production of any more virions.
E)The host cell produces an inhibitor that halts viral DNA replication after the first few virus genomes are produced.

Question 21

Discuss the evidence that mimiviruses may have transferred a gene from a bacterium to a eukaryote.Why would amoebae,the host cell of the mimivirus,be hypothesized to be sources of this type of horizontal gene transfer?

Question 22

Describe how the viruses that infect the marine coccolithophore Emiliania huxleyi can change local weather patterns.

Question 23

The famous white cliffs of Dover were formed by shells of a marine organism killed by coccolithoviruses.

Question 24

The enzymes encoded by the phycodnavirus PBCV-1 are notable because they are the largest known enzymes of their type found in a viral genome.

Question 25

The genome of the giant mimivirus contains more non-coding and "junk" DNA than most other DNA viruses.

Question 26

Chloroviruses,like PBCV-1,encode enzymes which can produce hyaluronan and chitin,two different saccharide polymers.