GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Genetic Cloning, Splicing, and Sequencing

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

varsity tutors app store varsity tutors android store

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept

Example Questions

← Previous 1

Example Question #1 : Help With Genetic Cloning, Splicing, And Sequencing

When performing heat shock transformation of a DNA plasmid into Escherichia coli, what purpose does the heat shock serve?

Possible Answers:

Introduce pores in the membrane

Denature the plasmid DNA

Stimulate Escherichia coli proliferation

Linearize the plasmid

Mask the negative charge of phosphate groups on DNA

Correct answer:

Introduce pores in the membrane

Explanation:

The correct answer is introduce membrane pores. Escherichia coli grows optimally at 37 degrees Celcius. However, an increase in temperature causes the plasma membrane to become more fluid, introducing small pores through which plasmid DNA can enter into the cell.

Example Question #2 : Help With Genetic Cloning, Splicing, And Sequencing

Two students receive 1 microliter of plasmid DNA that expressed beta-lactamase under a constitutive promoter, and green fluorescent protein (eGFP) under an arabinose inducible promoter. 

The students decide to heat shock transform the entire volume of plasmid DNA into chemically competent bacterial cells to ensure that they have enough replicated plasmid for future experiments. The students also transform the same volume of sterile water as a control. They plate their transformations on the following plates:

1. Nutrient agar

2. Nutrient agar plus ampicillin

3. Nutrient agar plus ampicillin and arabinose

The next day, the students observe a lawn of bacteria on each plate for bacterica transformed with the plasmid, with only 1/10 of the bacteria glowing green on plate 3. Additionally, they observe a lawn of bacteria on each plate for the control condition.

Which is most likely the cause of their results?

Possible Answers:

The heat shock transformation did not successfully introduce plasmid DNA into the bacteria

The ampicillin in the nutrient agar plates expired

There is not enough information given to interpret the results

The plasmid does not confer ampicillin resistance to the bacteria

The plasmid mutated and now expresses eGFP constitutively

Correct answer:

The ampicillin in the nutrient agar plates expired

Explanation:

The correct answer is the ampicillin the nutrient agar plates expired. The plasmid expresses beta-lactamase, an enzyme that degrades ampicillin. Successfully transformed bacteria will be able to grow in the presence of ampicillin, but untransformed bacteria should not grow. Since the bacteria in our control transformation do not have ampicillin resistance conferred by beta-lactamase, we would expect that no growth would be observed on any nutrient agar plates with ampicillin. However, we observe uncontrolled growth on these plates, indicating that the ampicillin has expired and is no longer a viable selectable marker for transformed bacteria. 

Example Question #3 : Help With Genetic Cloning, Splicing, And Sequencing

When performing a polymerase chain reaction, what is the purpose of the annealing temperature?

Possible Answers:

Annealing temperatures do not apply to polymerase chain reactions

The temperature at which the template DNA denatures

The temperature at which nucleotides are incorporated into the newly synthesizing DNA strand

The optimal temperature at which primers bind specifically to their complementary sequences

The optimal temperature at which DNA polymerase is active

Correct answer:

The optimal temperature at which primers bind specifically to their complementary sequences

Explanation:

The annealing temperature is the optimal temperature at which the primers bind the template DNA sequence. This temperature takes into account several factors: the number of basepairs in the primers, the relative guanine-cytosine content, and their melting point. 

Example Question #4 : Help With Genetic Cloning, Splicing, And Sequencing

A researcher wants to clone a bacterial gene into a mammalian expression vector for his project. Which of the following most accurately represents the chronological steps the researcher should take in order to successfully obtain the construct? 

Possible Answers:

Restriction digest the bacterial gene from genomic DNA, PCR amplify the vector backbone from genomic DNA, ligate the gene and vector backbone

Ligate the bacterial gene and vector backbone, PCR amplify the bacterial gene from cDNA, restriction digest the vector backbone

None of these

Restriction digest the bacterial gene from cDNA, restriction digest the vector backbone, PCR amplify the bacterial gene and vector backbone together

Restriction digest the vector backbone from genomic DNA, restriction digest the bacterial gene, ligate the bacterial gene and vector backbone

Correct answer:

None of these

Explanation:

None of the answer choices are correct. In order to successfully clone a bacterial gene into a mammalian expression vector, the following must be completed: First, the bacterial gene should be PCR amplified from bacterial cDNA, which contains only exons. Second, the vector backbone should be digested with restriction enzymes to linearize the vector so that the bacterial gene can be inserted at a specifc locus (multiple cloning site). Third, the amplified bacterial gene and the digested vector backbone are ligated together to create the desired expression construct. 

Example Question #5 : Help With Genetic Cloning, Splicing, And Sequencing

A student researcher wants to amplify a transcription factor gene from humans and clone it into an expression vector. What template should the student use for PCR? 

Possible Answers:

Primary amino acid chain

gDNA

cDNA

RNA

mRNA

Correct answer:

cDNA

Explanation:

The correct answer is cDNA. Given that this gene most likely has several introns, complementary DNA (cDNA) should be used as a template since it only contains exons. When subcloning a gene into an expression vector, only coding sequence should be present because the transcribed RNA will not be processed like it is in host cells.

Example Question #6 : Help With Genetic Cloning, Splicing, And Sequencing

Why are plasmids typically used in bacterial cloning and expression as opposed to linear fragments of DNA?

Possible Answers:

Plasmids do not replicate or express in bacterial hosts

Plasmid replication is dependent on host replication 

None of these

Linear fragments of DNA are in a heterochromatin state

Plasmids are not degraded by exonucleases

Correct answer:

Plasmids are not degraded by exonucleases

Explanation:

Plasmids are circular pieces of DNA that are resistant to exonucleic degradation (exonucleases cut from DNA ends). Bacteria harbor native plasmids that replicate independently from their genome and express genes that often confer a survival advantage. Scientists often clone genes into plasmids and express them in a variety of host cells. 

Example Question #6 : Help With Genetic Cloning, Splicing, And Sequencing

Which scientist was responsible for the development of, and was the namesake for, the first widely used automated DNA sequencing method?

Possible Answers:

E. M. Southern

Frederick Sanger

Leroy Hood

Craig Venter

Kary Mullis

Correct answer:

Frederick Sanger

Explanation:

Frederick Sanger invented the chain termination method of DNA sequencing in 1977, which has been widely used since its invention for short DNA sequences. The method is know as Sanger Sequencing. Leroy Hood was responsible for automating this method, Kary Mullis was the inventor of the polymerase chain reaction to create copies of DNA, E. M. Southern lent his name to another DNA study method called Southerns, and Craig Venter was responsible for other later DNA sequencing methods.

Example Question #7 : Help With Genetic Cloning, Splicing, And Sequencing

Polymerase chain reaction, or PCR, was developed to create copies of DNA molecules for study. Which of these facts about PCR is false?

Possible Answers:

PCR generally only uses one synthesized primer DNA sequence for the reaction.

5' to 3' RACE and quantitative PCR are two specialized PCR types.

There are three temperature steps to a normal PCR cycle.

PCR is generally run in a very precise machine called a thermal cycler.

Most PCR reactions use a polymerase engineered from the bacterium Thermus aquaticus to synthesize new DNA.

Correct answer:

PCR generally only uses one synthesized primer DNA sequence for the reaction.

Explanation:

Polymerase chain reaction requires two, not one, synthesized primer molecules to correctly amplify a DNA molecule into new copies. One primer attaches to each end of your desired DNA segment, and amplification occurs from these sites by polymerase molecules. The other options are all correct facts about PCR.

Example Question #8 : Help With Genetic Cloning, Splicing, And Sequencing

Although they are not commonly used for modern genome projects, cosmids were important vectors for moderate length DNA cloning and sequencing. Which vectors could handle larger DNA insert sizes?

I. Bacterial artificial chromosomes (BAC's)

II. Plasmids

III. Yeast artificial chromosomes (YAC's)

Possible Answers:

III only

II only

I and III

I, II, and III

None of these

Correct answer:

I and III

Explanation:

Cosmids could handle DNA insert sizes of 25-50kb. BAC's could handle insert sizes of 100-300kb, and YAC's even more. These are still used for tricky genome projects due to this large insert size, like antifreeze protein genes in Arctic fish. Plasmids can generally only handle insert sizes of 5-10kb.

Example Question #10 : Help With Genetic Cloning, Splicing, And Sequencing

What important advance in Sanger chain termination based DNA sequencing technique allowed for vast improvements in sequence data output?

Possible Answers:

Capillary chromatography

Thermostable polymerases

None of these

Four different fluorescent DNA tags

All of these

Correct answer:

All of these

Explanation:

These were all important advances in improvement of the Sanger technique that increased DNA sequence output. Modification of polymerases allowed quicker thermal cycling reactions and incorporation of manufactured bases with fluorescent tags. Four different fluorescent tags for each base allowed for easy identification of different bases. Lastly, capillary chromatography allowed for huge parallelization of DNA sequencing.

← Previous 1

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: