GRE Subject Test: Biology : Understanding RNAi

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #24 : Lab Techniques

Which of the following techniques could help a researcher inhibit the expression of a target gene?

Possible Answers:

RNAi

qPCR

X-ray crystallography

FPLC

Correct answer:

RNAi

Explanation:

RNA interference (RNAi) takes use of the cell's internal machinery to locate a target mRNA transcript and stall its translation, or degrade it completely. It is a very powerful tool for silencing genes. Small RNA transcripts bind to mRNA, either silencing translation or labeling the mRNA for destruction.

qPCR is a technique used to measure gene expression. FPLC is used to purify proteins. X-ray crystallography is used to elucidate protein structures.

Example Question #25 : Lab Techniques

Which of the following statements best describes the function of RNAi?

Possible Answers:

Interfere with translation by blocking a target mRNA

Globally interfere with translation by blocking all mRNA

Interfere with translation by targeting specific tRNA molecules

Interfere with translation by targeting ribosomes 

Correct answer:

Interfere with translation by blocking a target mRNA

Explanation:

RNAi is a process that utilizes small molecules of RNA (miRNA or siRNA) to target specific molecules of mRNA, repressing their translation or cleaving them into non-functional units. This essentially prevents the expression of a particular protein by neutralizing its mRNA transcript. Ribosomes may fail to bond with the region of double-stranded RNA, created from the mRNA and RNAi dimer, or it may attract nucleases.

RNAi is not involved in globally halting translation and is not used to target tRNA or ribosomes.

Example Question #26 : Lab Techniques

Dicer is an endonuclease that cleaves __________ during the process of RNA-interference.

Possible Answers:

single-stranded DNA

single-stranded RNA

transcription factor mRNA

double-stranded RNA

double-stranded DNA

Correct answer:

double-stranded RNA

Explanation:

Double-stranded RNA molecules are dicer's substrate, and their presence initiates the RNAi process. The other molecules listed are not cleaved by dicer proteins.

Example Question #1 : Understanding Rn Ai

Which protein, associated with the RNA-inducing silencing complex (RISC), activates and cleaves mRNA in RNAi? 

Possible Answers:

Endonuclease

Argonaute

RNA helicase 

None of these

RNase III Dicer 

Correct answer:

Argonaute

Explanation:

The correct answer is argonaute. Argonaute is part of the RISC and binds small non-coding RNAs. These RNAs guide argonaute to their specific targets via complementary base pairing, leading to mRNA cleavage and subsequent inhibition of translation. Dicer generates double-stranded RNA fragments, and endonucleases and RNA helicases are not specific to RNAi. 

Example Question #28 : Lab Techniques

Many strains of the model organism Drosophila have been engineered to express RNAi transgenes; that is, these transgenes express a moiety that is capable of targeting specific mRNAs to be degraded. This effectively results in downregulation of certain genes, permitting scientists to study how loss of that gene effects the organism. 

What is the structure of the RNAi moiety that targets and binds to specific mRNAs?

Possible Answers:

Single sheet polypeptide

Double stranded DNA

DNA-protein complex

Single stranded RNA

Double stranded RNA

Correct answer:

Double stranded RNA

Explanation:

RNAi molecules are double stranded RNAs. Their sequences are complementary to the sequence of the mRNA in which they are designed to destruct, thus allowing them to bind and trigger the degradation process. 

Example Question #29 : Lab Techniques

Many strains of the model organism Drosophila have been engineered to express RNAi transgenes; that is, these transgenes express a moiety that is capable of targeting specific mRNAs to be degraded. This effectively results in downregulation of certain genes, permitting scientists to study how loss of that gene effects the organism. 

Consider the following hypothetical situation. Gene A codes for the protein Enzyme A; that is, Gene A is expressed and is translated to make Enzyme A. You obtain a fly expressing an RNAi that targets Gene A's mRNA. If you express this RNAi in a fly (Drosophila), which of the following is the most likely result you'd expect if you were able to monitor Enzyme A levels with a fluorescent antibody and compared a wild-type fly to one expressing the RNAi?

Possible Answers:

Enzyme A levels would be reduced in the RNAi expressing fly, resulting in less fluorescence in the RNAi expressing fly.

Enzyme A levels would be increased and more fluorescence would be apparent in the RNAi expressing fly.

Enzyme A levels would be unchanged because RNAi targets mRNA, thus no differences in fluorescence would be apparent between wild-type and RNAi expressing flies. 

Enzyme A levels would be decreased in both the wild-type and RNAi expressing flies.

Enzyme A levels, and therefore fluorescence, would be decreased only in the nucleus of the RNAi expressing fly because this is where translation occurs.

Correct answer:

Enzyme A levels would be reduced in the RNAi expressing fly, resulting in less fluorescence in the RNAi expressing fly.

Explanation:

Since we can assume the RNAi correctly targets and degrades the proper mRNA, we can expect that the levels of Enzyme A will be decreased in the fly expressing the RNAi against Enzyme A. Because Gene A's mRNA will be degraded, little or no protein will be produced from Gene A, and thus the fluorescent antibody against Enzyme A will have nothing to bind to, which will result in less fluorescence in the fly expressing the RNAi versus the fly with undisturbed translation of the mRNA.

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