There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?

• It makes a repressor that binds CAP

• It cannot make a functional repressor

• It makes molecules that bind to one another

• It cannot bind to the inducer.

Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following?

• Eukaryotic mRNAs get 5' caps and 3' tails.

• Eukaryotic coded polypeptides often require cleaving of signal sequences before localization.

• Prokaryotic genes are expressed as mRNA, which is more stable in the cell.

• Eukaryotic exons may be spliced in alternative patterns.

You are given an experimental problem involving control of a gene's expression in the embryo of a particular species. One of your first questions is whether the gene's expression is controlled at the level of transcription or translation. Which of the following might best give you an answer?

• An analysis of amino acid production by the cell shows you that there is an increase at this stage of embryonic life.

• You measure the quantity of the appropriate pre-mRNA in various cell types and find they are all the same.

• You assess the position and sequence of the promoter and enhancer for this gene.

• You use an antibiotic known to prevent translation.

Refer to the treatments listed below to answer the following question:

You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent.

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

II. Filtering the substance to remove all elements smaller than what can be easily seen under a light microscope.

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

IV. Treating the sample with proteases that digest all proteins 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?

• I

• III

• II

• IV

Refer to the treatments listed below to answer the following question:

You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent.

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

II. Filtering the substance to remove all elements smaller than what can be easily seen under a light microscope.

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

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

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

• II only

• III only

• I only

• Either I or IV

The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others.

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.

• treatment of the HSV lesions to shorten the breakout

• education about avoiding sources of infection

• vaccination of all persons with preexisting cases.

The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others.

In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell-surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty". Which of the following best fits these observations?

• The viral envelope mediates entry into the cell, the cell capsid enters into the nuclear membrane, and the genome is all that enters the nucleus.

• Viral capsids are needed for the cell to become infected; only the capsids enter the nucleus

• Only the genetic material of the virus is involved in the cell's infectivity, and is injected like the genome of a phage.

• The viral capsid mediates entry into the cell, and only the genomic DNA enters the nucleus where it may or may not replicate.

Evidence suggests that factors which contribute towards the virulence of E. coli strain O157:H7, a bacterial strain reported to cause several food poisoning deaths, are caused by genes from a virus that infects bacteria. Considering this evidence, which statement most likely explains how the O157:H7 population acquired the genetic variation that distinguishes the strain from harmless E. coli strains, such as those that reside in our intestines?

• The virus entered the bacterial cell and incorporated its DNA into the bacterial genome, allowing the bacteria's cellular machinery to create new viruses.

• The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium.

• The virus entered the cell and acquired specific genes from the bacteria to increase the virulence of the virus.

• Viral envelope proteins bind to receptors on the bacterial membrane, allowing the viral genetic material to enter the bacterium and become translated into proteins.

In 2009, a flu pandemic was believed to have originated when viral transmission occurred from pig to human, thereby earning the designation "swine flu". ALthough pigs are thought to have been the breeding ground for the 2009 virus, sequences from bird, pig, and human viruses were all found within thin newly identified virus. What is the most likely explanation of why this virus contained sequences from bird, pig, and human viruses?

• The human was likely infected with various bacterial strains that contained all three RNA viruses.

• The infected individuals happened to be infected with all three virus types.

• Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly.

• The virus was descended from a common ancestor of bird, pig, and human flu viruses.

Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations?

• High mutation rate due to lack fo proofreading of RNA genome replication errors.

• Viral RNA is translated by host cell ribosomes

• Capsid proteins from the host cell can replace the viral capsid

• Transcription from the host cell RNA polymerase introduces numerous mutations.