All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #61 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
A scientist is trying to create a mutant cell line that has a specific non-functional protein. After many different mutagenesis techniques, he is unable to create a cell line with the mutation he desires. Which of the follow might be the reason he cannot generate a mutant for this protein?
The gene is buried deep within a region of heterochromatin
The gene is highly conserved throughout evolution
The mutant phenotype is lethal
The gene is buried deep within a region of euchromatin
The mutant phenotype is lethal
If he cannot generate a mutant, it is most likely because the mutant phenotype is lethal. In theory, this researcher was successful in mutating the target gene, however the result of the mutation was a failure during development. This would prevent any potential offspring with the mutation from developing, resulting in no viable specimens for the study.
Many proteins are conserved throughout evolution, but can still be easily mutated. For example, the gene for the protein hemoglobin is well-preserved between animal species, but can still be manipulated to generate animal models for various disorders. The distinction between heterochromatin and euchromatin doesn't really explain why the researcher would be unable to generate a mutant.
Example Question #62 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Which of the following techniques can be used for mutagenesis?
UV light exposure
PCR
Homologous recombination
All of these answers
All of these answers
All of the given answers could potentially be used in a mutagenesis procedure.
For PCR, special primers can be designed to introduce site-directed mutagenesis. UV light is a common mutagen and could be used to make random mutations throughout the genome. Homologous recombination can be used to incorporate a non-functional copy of a gene into an organism.
Example Question #63 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
In a knockout, what is a chimeric mouse?
A mouse homozygous for the knockout
A mouse derived from two different types of stem cells
A mouse heterozygous for the knockout
A mouse derived only from the modified stem cells
A mouse derived from two different types of stem cells
A chimeric mouse results from implanting altered stem cells into a fertile mother. Her offspring will consist of mice made partially of her own stem cells and partially from the stem cells that were implanted by the researcher. The term chimera does not necessarily reflect upon the genotype of the mice.
Example Question #64 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Which of the following gene editing technologies is not utilized to programmably alter/mutate specific genomic loci in uni/multicellular organisms?
None of these
Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9
Zinc-finger nucleases (ZFNs)
Restriction endonucleases
Transcription activator-like effector nucleases (TALENs)
Restriction endonucleases
CRISPR/Cas9 utilizes a gRNA sequence that directs the endonuclease activity of Cas9 to specific PAM recognition sites within the genome. TALENs harbor a DNA binding domain and a nuclease domain. Binding of the TALEN to a specific loci activates the nuclease domain to cut at that specific locus. ZFNs, similar to TALENs, have a Zinc-finger domain that binds specific DNA sequences and a DNA-cleavage domain. The above technologies are programmable to target varying genomic loci. Restriction endonucleases alone, however, are not utilized to stably alter genomes.
Example Question #65 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
A student researcher is trying to identify genes that are turned on by a specific transcription factor. Which of the following techniques can the student use?
All of these
Chromatin immunoprecipitation with sequencing
Transcription factor morpholino knockdown with microarray analysis
Chromatin immunoprecipitation with microarray analysis
Transcription factor morpholino knockdown with RNA sequencing
All of these
The correct answer is all of the answers. Chromatin immunoprecipitation with sequencing uses an antibody specific to the transcription factor to pull down crosslinked transcription factor-DNA complexes. Sequencing of this DNA then determines the promoters of genes that this transcription factor binds. Chromatin immunoprecipitation with microarray analysis is similar, however, the DNA bound in complex is analyzed by a designed microarray of select genes (promoters). Morpholinos are anti-sense DNA oligomers that prevent translation of their target genes, and as such, are an efficient way to knockdown gene expression. By knocking down a transcription factor, we can measure differentially regulated genes compared to a control. The read-out experiment for measuring up or down-regulated genes in the knockout condition can be either by RNA-sequencing or by microarray analysis.
Example Question #66 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Which of the following is not a way to disrupt the expression of a specific gene?
CRISPR/Cas9
Morpholino
Small interfering RNAs
None of these
Short hairpin RNAs
None of these
Morpholinos, short hairpin RNAs, and small interfering RNAs are methodologies to transiently knockdown the expression of a specific gene by complementary base pairing with the transcribed mRNA of gene of interest, inhibiting translation. CRISPR/Cas9 permanently mutates a gene of interest by introducing a double-stranded DNA break within the gene. All of these technologies are widely used in disruption of gene expression.
Example Question #67 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
When using the CRISPR/Cas9 gene editing technology, what genomic functional element does the Cas9 endonuclease recognize to indicate where it introduces a double stranded break?
Protospacer adjacent motifs
None of the other answers
Guide RNA
TATA box
Trans-activating CRISPR-RNA
Protospacer adjacent motifs
The correct answer is protospacer adjacent motifs (PAMs). gRNAs guide Cas9 to a specific genomic loci, however, in order for Cas9 to introduce a DNA break, a PAM, which are 5' NGG 3' sequences, must be present at the loci as well. TATA boxes are functional elements in eukaryotic promoters that promote activation of transcription. Trans-activating CRISPR-RNAs are important for pathogen defense in bacteria and archaea, but are not utilized in the gene editing technology.
Example Question #68 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
What is the purpose of adding sodium fluoride to a cell lysis buffer?
It is a serine/threonine phosphatase inhibitor
It is a cysteine protease inhibitor
It is a tyrosine phosphatase inhibitor
It is a serine protease inhibitor
It is a serine/threonine phosphatase inhibitor
Sodium fluoride is a serine/threonine phosphatase inhibitor. This is important to have in a cell lysis buffer if the protein of interest is phosphorylated. The presence of sodium fluoride will prevent the phosphoryl group from being removed by a serine/threonine phosphatase before it can be studied. It is often added to the cell lysis buffer along with sodium vanadate, which is a tyrosine/alkaline phosphatase inhibitor.
Example Question #69 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Which of the following techniques would best determine relative protein activity by its ability to bind specific DNA sequences in vitro?
Chromatin immunoprecipitation (ChIP)
Co-immunoprecipitation
Bradford protein assay
Electrophoretic mobility shift assay (EMSA)
Western blot
Electrophoretic mobility shift assay (EMSA)
The correct answer is electrophoretic mobility shift assay (EMSA). In an EMSA, specific DNA sequences are radioactively labelled and incubated with either protein lysates or purified proteins. The protein-DNA mixture is then loaded onto a non-denaturing gel to separate the proteins and DNA by size. DNA that is bound by protein will migrate more slowly than unbound DNA, which will migrate quickly. To detect radioactivity, a film is exposed to the gel, developed and interpreted. It is important to remember that the radioactivity is emitted by the DNA and not the protein.
Example Question #70 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Two students have cloned a bacterial DNA polymerase into a mammalian expression vector. The students then transfected the vector into human tissue culture cell lines to determine if the DNA polymerase retains its native function in human cells.
What technique is most suitable for the students to use to determine if the DNA polymerase is expressed in human cells?
Polymerase chain reaction (PCR)
Electroporation
Restriction digestion
Western blot
Electrophoretic mobility shift assay (EMSA)
Western blot
The correct answer is Western blot. In a Western blot, cell protein lysates are run on a denaturing gel and probed with a specific antibody. The student researchers can detect the existence of the DNA polymerase protein in the cell lysate using a specific antibody to that polymerase.
EMSAs determine a protein's ability to bind a DNA sequence, while electroporation, PCR, and restriction digests are not methods to detect protein expression.
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