Which one of the following proteins would most

| March 14, 2016

1. Which one of the following proteins would most likely be expressed constitutively?

A – RNA polymerase

B – Beta-galactosidase

C – Thiogalactoside transacetylase

D – Lactose permease

E – A tissue-specific transcription factor

2. Which of the following is least likely to be used as a form of regulation in living cells?

A – Using nucleases to degrade DNA when that region does not need to be expressed

B – Turning an enzyme on and off as the needs of the cell change

C – Feedback inhibition

D – Using proteases to degrade a protein that is no longer needed

E – Post-translational modification of proteins

3. Which one of the following statements about an E. coli culture growing in the presence of both glucose and lactose is incorrect?

A – At high glucose concentrations, the cells exhibit a strong growth curve.

B -The amount of beta-galactosidase increases as glucose gets depleted.

C – In the presence of glucose, no beta-galactosidase will be detectable.

D – As glucose supplies are exhausted, the cells enter a stationary phase of growth as they shift their metabolism to use the lactose.

E – With high amounts of glucose, the level of the enzyme beta-galactosidase is low.

4. Which one of the following is characteristic of the lac operon in E. coli?

A – Multiple genes

B – Monocistronic genes

C – A single stop codon

D – Multiple operator regions

E – mRNAs with 5′ caps

5 . Which of the following statements about the lacZ gene in E. coli is correct?

A – It is negatively regulated by a repressor protein that is bound to a lactose molecule.

B – When glucose and lactose levels are high, no ?-galactosidase is produced in the cell.
C – It is constitutively expressed.
D – It is under the control of a weak promoter.

E – It is transcribed independently from thelacY andlacA genes of thelac operon.

6. How is negative regulation lifted in the lac operon?

A – Lactose levels fall in the cell.
B – Glucose levels fall in the cell.
C – The Lac Repressor protein undergoes a conformational change when lactose is present.
D – CRP recruits RNA polymerase to the promoter.
E – None of the above; negative regulation is never lifted.

7. If a culture of E. coli is being grown with glucose and lactose as carbon sources, and levels of both sugars are high, which one of the following statements is correct?

A – CRP will not be expressed.
B – lacY will be expressed at its highest level.
C – The Lac Repressor will be bound to the lac operator, causing negative regulation.
D – The lac operon will be expressed at a low (but not basal) level.
E – Lac Repressor expression will be reduced.

8. An E. coli cell wants to control expression of Yfg protein. The mRNA has already been transcribed and is being stably maintained in the cell. How can translation of Yfg specifically be controlled?

A – An allosteric regulator can bind the Yfg protein and prevent it from being active.
B – The DNA can be degraded.
C – Non-preferred codons are used to specify key amino acids, and translation slows.
D – A repressor can bind to the promoter for the yfg gene.
E – All cellular ribosomes can be degraded, preventing translation of Yfg.

9. Which one of the following statements about phage is correct?

A – They enter the cells they infect through endocytosis.
B – They transfer genes from bacteria to animal cells.
C – They encode most of the enzymes and proteins required for intracellular metabolism and survival.
D – They are replicated only within bacterial cells.
E – They always contain circular RNA genomes.

10. Which one of the following describes an enzyme that a non-retroviral RNA virus would most likely have to provide on its own (or have produced from the viral genome)?

A – DNA polymerase
B – A DNA-dependent, RNA-synthesizing enzyme
C – Primase
D – Helicase
E – Replicase

11. Which one of the following is an example of a DNA virus?

A – Reverse transcriptase
C – T4
D – Capsid
E – Replicase

12. Arrange the replicative cycle of a human immunodeficiency virus in order from infection of a new cell [1] to release from that infected cell [8].

Viral RNAse H removes the RNA portion of a hybrid molecule, leaving ss-DNA

Assembly of new viral particles in the cytoplasm followed by budding off from the membrane

ss-DNA gets replicated to a ds-DNA, and together with integrase, is transported to the nucleus

Integrase incorporates viral DNA into the host chromosome

Release of viral ss-RNA genome and proteins into the cytoplasm

Viral reverse transcriptase synthesizes a DNA-RNA hybrid

HIV uses its glycoproteins to attach to host cells via the host’s CD4 receptors and co-receptors

Production of multiple copies of viral mRNA and proteins

13. For a bacteriophage which exhibits a clearly defined late gene expression stage in its replicative cycle, which one of the following would most likely occur during late gene expression?

A – Production of capsid proteins
B – Production of enzymes needed for replication of host genome
C – Production of membrane components needed to envelop the viruses following release from host cell
D – Production of enzymes needed to degrade host genome
E – Production of enzymes needed for replication of viral genome

14. Which one of the following is an activity of reverse transcriptase?

A – Proteolysis
B – DNA-dependent RNA synthesis
C – RNA-dependent RNA synthesis
D – RNA degradation
E – Phosphorylation

15. Which one of the following statements about T4 is correct?

A – The genes expressed early in its replicative cycle are under the control of a weak promoter.
B – It expresses a replicase enzyme in the early stage of its replicative cycle.
C – The capsid, tail fiber protein, and base protein are examples of proteins expressed early in its replicative cycle.
D – It expresses nucleases during early gene expression to degrade the host genome, thus diverting resources to viral production.
E – Upon attachment to a cell surface, the capsid injects a double-stranded RNA to the host cytosol.

16. Which one of the following enzymes is an RNA virus most likely to use to directly replicate its genome?

A – Primase
B – DNA polymerase I
C – DNA polymerase III
D – RNA polymerase I
E – Reverse transcriptase

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