Chapter 9 mini quiz

Give two reasons why a universal phylogenetic tree of viruses may prove hard to construct

1. The highly diverse sequence variation in the viral genomes 2. The scrambled genomes of all known viruses that make it difficult to link them evolutionarily

Compared with other archaeal viruses, what are two unusual features of the virus that infects Acidianus

1. These viuses change their shape from a lemon shape to one with long and thin tails at either ends after their release from host cells. 2. These viruses are lysogenic when most other archaeal viruses are lytic.

what is unusual about the envelope of a herpes virus

Its unusual because it is produced from the nuclear envelope of the host cells through a budding process. The envelopes of other enveloped virus are produced from the cytoplasimsic membrane from host cells.

Why are protease inhibitors an effective treatment for human AIDS

Because AIDs consist of many additional small genes for this virus to express itself. Extensive processing of proteins of proteins by protase enzymes is necessary. It also requires alternative splicing of introns from its genome in order to express. Thus, by having particular protease inhibitors you can stop the virus.

Contrast the genome of HIV and Hepatitis B

HIV comprises of two identical RNA copies. HepB is comprised of DNA that is present as partially ds Structure. They utilize reverse transcriptase differently. HIV occurs through a DNA intermediate. Whereas HepB involves an NA intermediate.

How can the outcome of an SV40 viral infection differ in permissive versus nonpermissive

In permissive the SV40 viral infection takes the lytic approach where the virions are released from lysis of host. in nonpermissive hosts the viruses do not lyse. Their genomes integrate within the host genome. This changes the host cell genomes which can transform the host cells into malignant cells.

What is unusual about the replication mechanism of the Mu genome

It involves transposition. The replication in these phages involves the enzyme transposase and replication occurs with its genome as a constituent of a larger genome. In short, the Mu bacteriophage necessarily integrates its own genome with the host genome and the enzyme transposase which is important for integration.

In influenza virus, what is antigenic shift and how does it occur

It occurs by reassorting of RNA genomes of two different strains of the virus that have infected a same cell. This reassortment results in the formation of virions that are hybrids of the parent strains and have different antigenic profile compared to the two parental strains.

Explain how viruses could have "invented" the genetic material found in cells

Its sugested that RNA was the first genetic material in primordial life forms. The DNA as is commonly present in most life forms currently would have formed from primordial RNA. Thus, RNA viruses which are more primitive are thought to have invented DNA.

How can poliovirus RNA be synthesized in the cytoplasm whereas host RNA must be made in the nucleus

Its synthesized in the cytoplasm of the host cells because the genome of the poliovirus binds to the host cells ribosomes. The RNA replicase enzyme helps in the synthesis of viral mRNA. (both the plus and minus strands)

Contrast mRNA production in the two classes of single-stranded RNA viruses

Positive strand have mRNA as the genome and hence the mRNA production is direct. Negative strands have to synthesize RNA plus strand from the negative strand template which functions as the mRNA

How does a prion differ from viriod.

Prions are infectious proteins and have the native/pathogenic forms as different by their secondary structures. Viroids are RNA molecules devoid of protein.

On what basis can prions be differentiated from all other infectious agents

Prions are infectious proteins. They differ because these are only infectious agents. they do not consist of nucleic acids, either DNA or RNA.

In what major way does transcription of phage DNA differ in phage T4 and T7

The T4 phage utilizes the RNA polymerase from host host cells for the transcription process. T7 phages utilize their own RNA polymerase for the transcription process

What is a segmented genome

The genome is often divided up into separate parts. All segments are not required to be in the same virion for the virus to be infectious.

What is unusual about genetic information flow in retroviruses

The information flow is from RNA to DNA which is known as reverse transcription. Its catalyzed by the enzyme called reverse transcriptase.

What is the difference between the native and pathogenic forms of the prion protein

The major difference is in their secondary structures. The native prion has an alpha-Helix The infectious prion has a beta-Helix.

What type of genome is seen most in archaeal viruses

The most commonly seen are of the DNA type. Most contain dsDNA and a circular DNA genome.

What is present in the poliovirus polyprotein

The polyprotein consists of virion structural proteins. The VPg protein, RNA replicase, and a virus-encoded protease.

Distinguish between Positive and Negative strand RNA virus

The positive strands have mRNA as the genome. The negative strands have the RNA genome that is complementary to mRNA

How does the role of transcriptase in the replication cycles of retroviruses and Hepadnaviruses

The retrovirus contains two RNA copies. It uses reverse transcriptase to make one of those RNA copies into DNA. Hepadnaviruses also uses reverse transcriptase for replication. But it replicates its DNA by the use of an RNA intermediate. After DNA is formed, the viral reverse transcriptase enzyme copies it and packages in into the virion head.

What is unusual about genome replication in adenoviruses

The unusual feature is that the genomic replication process occurs from both directions of the DNA template strands in a leading manner. Usually replication while one strand progress in the leading direction, the other proceeds as a lagging strand.

Why is the adenoviruses terminal protein essential for replicating its genome

They contain terminal protein attached to the 5' end. This protein is essential for the genomic replication, the proteins help in the replication process that start at the two ends of the genome.

How could viruses have accelerated the evolution of cells

They could have helped due to their mode of functioning. The lysogentic and latent periods integrate their genome into the host cell genome which can induce genetic variation.

If viriods are circular molecules, why are they depicted as hairpins

This is due to the configuration it has as a result of extensive folding in its secondary structure.

Why must reoviral replication events occur within the nucleocapsid

Upon infection the reoviruses are taken up by the host cell lysosomes from where they are released into the cytoplasm. The genome of these viruses contain dsRNA and require replicating enzymes of their own for the synthesis of mRNA. Also the dsRNA are seen as "non-self" by the host and will be destroyed. which is why it occurs in the nucleocapsid to prevent genomic destruction by host.

How might viriods cause disease in plants

Viroids are circular ssRNA. They gain entry into the plants cells through wounds and use of plasmodesmata for their movement between plants. They induce diseases by a mechanism as similar to siRNA (small interfering ribonucleic acids). These siRNA's which are produced as a result of viroid replication cause disturbance in the host cell functioning by silencing certain genes important for normal functioning.

What is unusual about genome replication in pox viruses

What is unusual is that all genomic replication steps involved occur in the cytoplasm of the host cell. Whereas normally they would happen in the hosts nucleus.

What does the reovirus genome consist of

dsRNA as their genetic materiel. Nonenveloped nucleocapsid. Have virus encoded enzymes that are required in synthesis of mRNA and replication of RNA genome. Also have a segmented genome that is seprated into 10-12 segments of linear dsRNA.