Viruses & Genome Evolution

Why is it unwise to try to relate an organism's complexity with its size or number of cells?

A single-celled organism, such as a bacterium or a protist, still has to conduct all the complex life functions of a large multicellular organism.

What is the function of reverse transcriptase in retroviruses?

It uses viral RNA as a template for DNA synthesis.

Which of the following is a representation of gene density?

Humans have ~20,000 genes in 2,900 Mb.

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have

T4 protein and T4 DNA.

A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur?

The plants would develop the typical symptoms of TMV infection.

Which of the following represents a difference between viruses and viroids?

Viruses have capsids composed of protein, whereas viroids have no capsids.

What is the most probable explanation for the continued presence of pseudogenes in a genome such as our own?

They are genes that are not expressed, even though they have nearly identical sequences to expressed genes.

Which of the following describes plant virus infections?

They are spread via the plasmodesmata.

Which procedure is not required when the shotgun approach to sequencing is modified as sequencing by synthesis, in which many small fragments are sequenced simultaneously?

cloning each fragment into a plasmid

Which of the following most correctly describes a shotgun technique for sequencing a genome?

cloning several sizes of fragments into various size vectors, ordering the clones, and then sequencing them

What is bioinformatics?

a method that uses very large national and international databases to access and work with sequence information

In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following would you expect of the genes of the bacteriophage?

control of more than one gene in an operon

Which of the following accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of his or her life?

copies of the herpesvirus genome permanently maintained in host nuclei

Which of the three types of viruses shown above would you expect to include a capsid(s)?

all three

Viral envelopes can best be analyzed with which of the following techniques?

antibodies against specific proteins not found in the host membranes

RNA viruses require their own supply of certain enzymes because

host cells lack enzymes that can replicate the viral genome.

Homeotic genes

encode transcription factors that control the expression of genes responsible for specific anatomical structures.

Bioinformatics can be used to scan sequences for probable genes looking for start and stop sites for transcription and for translation, for probable splice sites, and for sequences known to be found in other known genes. Such sequences containing these elements are called

expressed sequence tags.

What is gene annotation in bioinformatics?

finding transcriptional start and stop sites, RNA splice sites, and ESTs

A multigene family is composed of

genes whose sequences are very similar and that probably arose by duplication.

Which of the following characteristics, structures, or processes is common to both bacteria and viruses?

genetic material composed of nucleic acid

Which of the following can be effective in preventing the onset of viral infection in humans?

getting vaccinated

In the figure, at the arrow marked II, what enzyme(s) are being utilized?

host cell DNA polymerase

Which viruses have single-stranded RNA that acts as a template for DNA synthesis?

retroviruses

) Which of the following can be duplicated in a genome?

sequences, chromosomes, or sets of chromosomes

What is metagenomics?

sequencing DNA from a group of species from the same ecosystem

Viral genomes vary greatly in size and may include from four genes to several hundred genes. Which of the following viral features is most apt to correlate with the size of the genome?

size and shape of the capsid

The comparison between the number of human genes and those of other animal species has led to many conclusions, including

the number of proteins expressed by the human genome is far more than the number of its genes.

The host range of a virus is determined by

the proteins on its surface and that of the host.

What is proteomics?

the study of the full protein set encoded by a genome

Which of the following is characteristic of the lytic cycle?

A large number of phages are released at a time.

Which of the following series best reflects what we know about how the flu virus moves between species?

An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted to humans.

What is the difference between a linkage map and a physical map?

For a linkage map, markers are spaced by recombination frequency, whereas for a physical map they are spaced by numbers of base pairs (bp).

Which of the three types of viruses shown above would you expect to include glycoproteins?

I and II only

Which treatment could definitively determine whether or not the component is a viroid?

I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious

If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities?

III. culturing the substance by itself on nutritive medium, away from any plant cells

Which treatment would you use to determine if the agent is a prion?

IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious

Why do RNA viruses appear to have higher rates of mutation?

Replication of their genomes does not involve proofreading

Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host?

The newly emerging virus will die out rather quickly or will mutate to be far less lethal.

Which of the following statements describes the lysogenic cycle of lambda (λ) phage?

The phage genome replicates along with the host genome.

Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory?

Viral genomes are usually similar to the genome of the host cell.

Which of the following studies would not likely be characterized as eco-devo?

a comparison of the functions of a particular homeotic gene among four species of reptiles

Which of the following is the best predictor of how much damage a virus causes?

ability of the infected cell to undergo normal cell division

To cause a human pandemic, the H5N1 avian flu virus would have to

become capable of human-to-human transmission.

If scientists are trying to use what they know about HSV to devise a means of protecting other people from being infected, which of the following would have the best chance of lowering the number of new cases of infection?

interference with new viral replication in preexisting cases

Antiviral drugs that have become useful are usually associated with which of the following properties?

interference with viral replication

What are prions?

misfolded versions of normal brain protein

The biggest problem with the shotgun technique is its tendency to underestimate the size of the genome. Which of the following might best account for this?

missing some duplicated sequences

Emerging viruses arise by

mutation of existing viruses, the spread of existing viruses to new host species, and the spread of existing viruses more widely within their host species.

In the figure, when new viruses are being assembled (IV), what mediates the assembly?

nothing; they self-assemble

Homeotic genes contain a homeobox sequence that is highly conserved among very diverse species. The homeobox is the code for that domain of a protein that binds to DNA in a regulatory developmental process. Which of the following would you then expect?

that homeotic genes are selectively expressed over developmental time

One of the characteristics of retrotransposons is that

they code for an enzyme that synthesizes DNA using an RNA template.

Fragments of DNA have been extracted from the remnants of extinct woolly mammoths, amplified, and sequenced. These can now be used to

understand the evolutionary relationships among members of related taxa.

Bioinformatics includes all of the following except

using molecular biology to combine DNA from two different sources in a test tube.

How is a physical map of the genome of an organism achieved?

using restriction enzyme cutting sites

The difference between vertical and horizontal transmission of plant viruses is that

vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant.