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All questions of Control of Gene Expression in Prokaryotes and Eukaryotes (BIO) for MCAT Exam
In a bacteria possessing the lac operon, which of the following occurs when glucose is low and lactose is abundant?- a)Beta-galactosidase acetylases the operon
- b)Lactose permease cleaves lactose to glucose and galactose
- c)Lactose metabolism is increased by lactose binding to the operon
- d)Transport of lactose into the cell is enhanced
Correct answer is option 'D'. Can you explain this answer?
In a bacteria possessing the lac operon, which of the following occurs when glucose is low and lactose is abundant?
a)
Beta-galactosidase acetylases the operon
b)
Lactose permease cleaves lactose to glucose and galactose
c)
Lactose metabolism is increased by lactose binding to the operon
d)
Transport of lactose into the cell is enhanced
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Carter Mitchell answered |
Transport of lactose into the cell is enhanced
When glucose levels are low and lactose is abundant in a bacterium with the lac operon, the following events occur:
- Induction of the lac operon: The lac operon is activated in response to low glucose levels and the presence of lactose. This leads to the expression of genes involved in lactose metabolism.
- Lactose binds to the repressor: In the absence of glucose and the presence of lactose, lactose binds to the lac repressor protein. This causes a conformational change in the repressor, preventing it from binding to the operator region of the lac operon.
- Enhanced transport of lactose: Lactose permease, a membrane protein encoded by the lac operon, is responsible for transporting lactose into the cell. When the lac operon is induced, more lactose permease is produced, leading to an increase in the transport of lactose into the bacterial cell.
- Lactose metabolism: Once inside the cell, lactose is cleaved by the enzyme beta-galactosidase into glucose and galactose. This allows the bacterium to utilize lactose as a carbon source in the absence of glucose.
Therefore, when glucose is low and lactose is abundant, the lac operon is activated, leading to enhanced transport of lactose into the cell, ultimately allowing the bacterium to metabolize lactose for energy production.
When glucose levels are low and lactose is abundant in a bacterium with the lac operon, the following events occur:
- Induction of the lac operon: The lac operon is activated in response to low glucose levels and the presence of lactose. This leads to the expression of genes involved in lactose metabolism.
- Lactose binds to the repressor: In the absence of glucose and the presence of lactose, lactose binds to the lac repressor protein. This causes a conformational change in the repressor, preventing it from binding to the operator region of the lac operon.
- Enhanced transport of lactose: Lactose permease, a membrane protein encoded by the lac operon, is responsible for transporting lactose into the cell. When the lac operon is induced, more lactose permease is produced, leading to an increase in the transport of lactose into the bacterial cell.
- Lactose metabolism: Once inside the cell, lactose is cleaved by the enzyme beta-galactosidase into glucose and galactose. This allows the bacterium to utilize lactose as a carbon source in the absence of glucose.
Therefore, when glucose is low and lactose is abundant, the lac operon is activated, leading to enhanced transport of lactose into the cell, ultimately allowing the bacterium to metabolize lactose for energy production.
What is an operon?- a)A protein that binds to an RNA segment and blocks the attachment of DNA polymerase, halting transcription
- b)A reversibly-bound protein that enhances the transcription of a particular segment of RNA
- c)A unit of DNA containing a cluster of genes under control of a promoter and a repressor
- d)A protein around which DNA is coiled until it is transcribed; also the chief protein component of chromatin
Correct answer is option 'C'. Can you explain this answer?
What is an operon?
a)
A protein that binds to an RNA segment and blocks the attachment of DNA polymerase, halting transcription
b)
A reversibly-bound protein that enhances the transcription of a particular segment of RNA
c)
A unit of DNA containing a cluster of genes under control of a promoter and a repressor
d)
A protein around which DNA is coiled until it is transcribed; also the chief protein component of chromatin
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Orion Classes answered |
An operon is a regulatory unit in bacterial and some eukaryotic genomes that consists of a cluster of genes with related functions, along with the regulatory elements that control their expression. It typically includes a promoter, operator, and one or more structural genes. The promoter is the DNA sequence where RNA polymerase binds to initiate transcription. The operator is a regulatory region where a repressor protein can bind and control the transcription of the genes within the operon.
The operon concept was first described by François Jacob and Jacques Monod in their studies of the lac operon in E. coli. The operon allows for the coordinated expression of multiple genes involved in a specific metabolic pathway or cellular function. By controlling the expression of these genes together, the cell can efficiently respond to environmental changes and regulate the production of proteins needed for specific functions.
Which of the following is NOT a function of the 5’ terminus of mRNA?- a)Promotes polyadenylation of the 3’ terminus
- b)Regulates nuclear export of mRNA
- c)Protects the mRNA from degradation
- d)Promotes ribosomal binding for translation
Correct answer is option 'A'. Can you explain this answer?
Which of the following is NOT a function of the 5’ terminus of mRNA?
a)
Promotes polyadenylation of the 3’ terminus
b)
Regulates nuclear export of mRNA
c)
Protects the mRNA from degradation
d)
Promotes ribosomal binding for translation
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Orion Classes answered |
The 5’ terminus of mRNA is involved in various functions, but promoting polyadenylation of the 3’ terminus is not one of them. Polyadenylation is the process of adding a poly(A) tail to the 3’ end of mRNA and is important for stability and translation efficiency.
Which of the following is a mechanism of transcriptional gene control?- a)Alternative splicing
- b)mRNA degradation
- c)DNA methylation
- d)Protein phosphorylation
Correct answer is option 'C'. Can you explain this answer?
Which of the following is a mechanism of transcriptional gene control?
a)
Alternative splicing
b)
mRNA degradation
c)
DNA methylation
d)
Protein phosphorylation
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Orion Classes answered |
DNA methylation is a mechanism of transcriptional gene control that can influence gene expression by affecting the accessibility of DNA to transcription factors and RNA polymerase. It can lead to the repression or silencing of specific genes.
Micro RNA (miRNA) primarily aids in transcriptional and post-transcriptional regulation by which method?- a)RNA editing via deamination of specific DNA sequences
- b)Cleavage of telomeres from 5’ termini
- c)Gene amplification through binding directly to critical DNA promoter regions
- d)Gene silencing through translational repression or target degradation
Correct answer is option 'D'. Can you explain this answer?
Micro RNA (miRNA) primarily aids in transcriptional and post-transcriptional regulation by which method?
a)
RNA editing via deamination of specific DNA sequences
b)
Cleavage of telomeres from 5’ termini
c)
Gene amplification through binding directly to critical DNA promoter regions
d)
Gene silencing through translational repression or target degradation
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Orion Classes answered |
MicroRNAs (miRNAs) primarily function in gene regulation by silencing gene expression at the post-transcriptional level. They do so through translational repression or target degradation.
When miRNAs bind to target messenger RNA (mRNA) molecules, they can inhibit translation, preventing the synthesis of the corresponding protein. This translational repression occurs through base pairing between the miRNA and the complementary sequences on the target mRNA, leading to the formation of an RNA-induced silencing complex (RISC). The RISC complex inhibits translation initiation or promotes mRNA degradation, ultimately reducing the protein levels.
What is the role of an activator?- a)Enhances interaction between RNA polymerase and the promoter
- b)Binds to an operon and transcribes RNA
- c)Causes conformational changes in the DNA, bringing promoter regions into proximity with enhancer regions
- d)Displaces a repressor protein from an operon, allowing RNA polymerase to proceed in transcription
Correct answer is option 'A'. Can you explain this answer?
What is the role of an activator?
a)
Enhances interaction between RNA polymerase and the promoter
b)
Binds to an operon and transcribes RNA
c)
Causes conformational changes in the DNA, bringing promoter regions into proximity with enhancer regions
d)
Displaces a repressor protein from an operon, allowing RNA polymerase to proceed in transcription
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Orion Classes answered |
The role of an activator is to enhance the interaction between RNA polymerase and the promoter region of a gene. Activator proteins are transcription factors that bind to specific DNA sequences known as enhancer regions, which are usually located upstream or downstream of the promoter. By binding to the enhancer, the activator protein can interact with other components of the transcription machinery, including RNA polymerase, and facilitate their recruitment to the promoter.
The activator protein helps to stabilize the formation of the transcription initiation complex and promotes efficient transcriptional initiation. It can also interact with other coactivator proteins to enhance the transcriptional activity of RNA polymerase.
Deacetylation of histones has which of the following effects?- a)Uncoiling of histone structure, preventing it from being accessed by transcriptional machinery
- b)Uncoiling of histone structure, allowing it to be accessed by transcriptional machinery
- c)Coiling of the histone structure, allowing it to be accessed by transcriptional machinery
- d)Coiling of the histone structure, preventing it from being accessed by transcriptional machinery
Correct answer is option 'D'. Can you explain this answer?
Deacetylation of histones has which of the following effects?
a)
Uncoiling of histone structure, preventing it from being accessed by transcriptional machinery
b)
Uncoiling of histone structure, allowing it to be accessed by transcriptional machinery
c)
Coiling of the histone structure, allowing it to be accessed by transcriptional machinery
d)
Coiling of the histone structure, preventing it from being accessed by transcriptional machinery
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Orion Classes answered |
Deacetylation of histones involves the removal of acetyl groups from histone proteins, leading to the tightening or coiling of the chromatin structure. This compacted state of chromatin makes it less accessible to the transcriptional machinery, such as transcription factors and RNA polymerase, thereby inhibiting gene expression.
What is the role of a repressor protein in gene regulation?- a)Enhancing transcription
- b)Initiating translation
- c)Activating enhancers
- d)Inhibiting transcription
Correct answer is option 'D'. Can you explain this answer?
What is the role of a repressor protein in gene regulation?
a)
Enhancing transcription
b)
Initiating translation
c)
Activating enhancers
d)
Inhibiting transcription
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Orion Classes answered |
Repressor proteins bind to specific DNA sequences, such as operator regions, and prevent the binding of RNA polymerase or other transcription factors to inhibit transcription. They play a role in negative regulation of gene expression.
Which of the following is an epigenetic modification involved in gene control?- a)DNA replication
- b)DNA methylation
- c)RNA splicing
- d)Transcription initiation
Correct answer is option 'B'. Can you explain this answer?
Which of the following is an epigenetic modification involved in gene control?
a)
DNA replication
b)
DNA methylation
c)
RNA splicing
d)
Transcription initiation
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Orion Classes answered |
DNA methylation is an epigenetic modification that involves the addition of a methyl group to cytosine residues in DNA. Methylation can regulate gene expression by blocking the binding of transcription factors or recruiting proteins involved in chromatin remodeling, ultimately influencing transcription and gene control.
The binding of a transcription factor to an enhancer region is likely to result in:- a)Repression of gene expression
- b)Activation of gene expression
- c)Termination of transcription
- d)mRNA degradation
Correct answer is option 'B'. Can you explain this answer?
The binding of a transcription factor to an enhancer region is likely to result in:
a)
Repression of gene expression
b)
Activation of gene expression
c)
Termination of transcription
d)
mRNA degradation
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Orion Classes answered |
Transcription factors binding to enhancer regions can enhance gene expression by recruiting the transcriptional machinery and promoting the initiation of transcription. Enhancers are DNA sequences that can be located far from the gene they regulate and can interact with the promoter region to enhance transcriptional activity.
Which of the following is a key component of the RNA-induced silencing complex (RISC) involved in RNA interference?- a)Small interfering RNA (siRNA)
- b)Ribosomal RNA (rRNA)
- c)Messenger RNA (mRNA)
- d)Transfer RNA (tRNA)
Correct answer is option 'A'. Can you explain this answer?
Which of the following is a key component of the RNA-induced silencing complex (RISC) involved in RNA interference?
a)
Small interfering RNA (siRNA)
b)
Ribosomal RNA (rRNA)
c)
Messenger RNA (mRNA)
d)
Transfer RNA (tRNA)
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Orion Classes answered |
Small interfering RNA (siRNA) molecules are key components of the RNA-induced silencing complex (RISC) involved in RNA interference (RNAi). siRNAs guide RISC to target mRNA molecules, leading to their degradation and silencing of gene expression.
Which of the following is an example of a global gene regulatory mechanism in eukaryotic cells?- a)DNA replication
- b)RNA editing
- c)Histone acetylation
- d)DNA repair
Correct answer is option 'C'. Can you explain this answer?
Which of the following is an example of a global gene regulatory mechanism in eukaryotic cells?
a)
DNA replication
b)
RNA editing
c)
Histone acetylation
d)
DNA repair
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Orion Classes answered |
Histone acetylation is an example of a global gene regulatory mechanism that affects chromatin structure and gene expression on a larger scale. It involves the addition of acetyl groups to histone proteins, leading to a more relaxed chromatin state and increased transcriptional activity.
Methylation of CpG islands is essential to which process(es)?- a)Stable silencing of DNA as cells terminally differentiate
- b)Enhancing cell differentiation into different organ systems with distinct functions
- c)Reversible inactivation of genes as cells terminally differentiate
- d)Enhancing oncogenic potential of rapidly-differentiating cells
Correct answer is option 'A'. Can you explain this answer?
Methylation of CpG islands is essential to which process(es)?
a)
Stable silencing of DNA as cells terminally differentiate
b)
Enhancing cell differentiation into different organ systems with distinct functions
c)
Reversible inactivation of genes as cells terminally differentiate
d)
Enhancing oncogenic potential of rapidly-differentiating cells
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Orion Classes answered |
Methylation of CpG islands, which are regions of DNA rich in CpG dinucleotides, plays a crucial role in the stable silencing of DNA during cellular differentiation. CpG islands are often found in the promoter regions of genes, and methylation of these CpG sites can lead to gene silencing by inhibiting the binding of transcription factors and other proteins necessary for gene expression. This process is particularly important during cellular differentiation when specific sets of genes need to be turned off or silenced in order to establish and maintain specialized cell types with distinct functions.
A proto-oncogene can be converted to an oncogene by all of the following EXCEPT:- a)Gene deletions
- b)Increased repressor binding
- c)Gene amplification
- d)Chromosomal rearrangement
Correct answer is option 'B'. Can you explain this answer?
A proto-oncogene can be converted to an oncogene by all of the following EXCEPT:
a)
Gene deletions
b)
Increased repressor binding
c)
Gene amplification
d)
Chromosomal rearrangement
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Orion Classes answered |
A proto-oncogene is a normal gene that has the potential to become an oncogene, which is a gene that promotes cancer development. Various genetic alterations can convert a proto-oncogene into an oncogene. These alterations can lead to uncontrolled cell growth and division, contributing to tumor formation.
Increased repressor binding: This option does not represent a mechanism for the conversion of a proto-oncogene into an oncogene. Increased binding of repressor proteins to a proto-oncogene would generally inhibit its expression and reduce its potential to promote cancer development.
What is the function of the spliceosome?- a)To condense DNA into small, manageable units
- b)To cause conformational changes in DNA that are amenable to splicing
- c)To cleave introns from RNA and ligate the cut ends
- d)To cleave telomeres prior to transcription
Correct answer is option 'C'. Can you explain this answer?
What is the function of the spliceosome?
a)
To condense DNA into small, manageable units
b)
To cause conformational changes in DNA that are amenable to splicing
c)
To cleave introns from RNA and ligate the cut ends
d)
To cleave telomeres prior to transcription
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Orion Classes answered |
The spliceosome is a complex of RNA and proteins that plays a crucial role in the process of RNA splicing. RNA splicing is a post-transcriptional modification in which introns, non-coding regions within a pre-mRNA molecule, are removed and the remaining exons are joined together to produce a mature mRNA molecule that can be translated into a protein.
The spliceosome recognizes specific sequences at the boundaries of introns, known as splice sites, and catalyzes the cleavage of the RNA at these sites. It then brings together the adjacent exons and ligates them, resulting in the removal of the intron and the formation of a continuous coding sequence.
In summary, the function of the spliceosome is to cleave introns from RNA molecules and ligate the cut ends, allowing for the production of mature mRNA molecules that can be translated into proteins.
Which of the following is an example of a post-transcriptional modification involved in gene control?- a)DNA methylation
- b)Promoter binding
- c)Alternative splicing
- d)RNA polymerase activity
Correct answer is option 'C'. Can you explain this answer?
Which of the following is an example of a post-transcriptional modification involved in gene control?
a)
DNA methylation
b)
Promoter binding
c)
Alternative splicing
d)
RNA polymerase activity
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Orion Classes answered |
Alternative splicing is a post-transcriptional modification in which different exons of a gene can be selectively included or excluded during mRNA processing. This process allows for the production of multiple mRNA isoforms and different protein products from a single gene.
Which of the following is a key regulatory protein involved in the lac operon of E. coli?- a)RNA polymerase
- b)Repressor protein
- c)Inducer molecule
- d)Operator sequence
Correct answer is option 'B'. Can you explain this answer?
Which of the following is a key regulatory protein involved in the lac operon of E. coli?
a)
RNA polymerase
b)
Repressor protein
c)
Inducer molecule
d)
Operator sequence
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Orion Classes answered |
In the lac operon of E. coli, the repressor protein binds to the operator sequence and inhibits transcription when lactose is absent. The presence of an inducer molecule (C), such as lactose or allolactose, prevents the repressor protein from binding to the operator, allowing RNA polymerase (A) to transcribe the genes involved in lactose metabolism.
The effect of allolactose is:- a)Enhancement of binding of RNA polymerase to DNA, increasing gene transcription
- b)Repression of the lac operon when glucose is present
- c)Conformational change in the repressor protein, inducing the lac operon
- d)Dissociation of RNA polymerase from DNA, terminating transcription of genes regulated by the lac operon
Correct answer is option 'C'. Can you explain this answer?
The effect of allolactose is:
a)
Enhancement of binding of RNA polymerase to DNA, increasing gene transcription
b)
Repression of the lac operon when glucose is present
c)
Conformational change in the repressor protein, inducing the lac operon
d)
Dissociation of RNA polymerase from DNA, terminating transcription of genes regulated by the lac operon
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Orion Classes answered |
Allolactose, an isomer of lactose, acts as an inducer of the lac operon in bacteria. When allolactose is present, it binds to the lac repressor protein, causing a conformational change in the repressor. This conformational change prevents the repressor from binding to the operator region of the lac operon.
As a result, the lac operon is derepressed, allowing for the transcription and expression of the genes involved in lactose metabolism.
Therefore, option C is the correct answer as it describes the effect of allolactose on inducing the lac operon by inducing a conformational change in the repressor protein.
In eukaryotic cells, which protein complex is responsible for the unwinding of DNA during transcription?- a)DNA polymerase
- b)RNA polymerase
- c)Helicase
- d)Topoisomerase
Correct answer is option 'B'. Can you explain this answer?
In eukaryotic cells, which protein complex is responsible for the unwinding of DNA during transcription?
a)
DNA polymerase
b)
RNA polymerase
c)
Helicase
d)
Topoisomerase
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Orion Classes answered |
During transcription, RNA polymerase is responsible for unwinding the DNA double helix and synthesizing an RNA molecule using one of the DNA strands as a template. DNA polymerase (A) is primarily involved in DNA replication, while helicase (C) and topoisomerase (D) are involved in DNA unwinding and supercoiling regulation.
Which of the following is a characteristic of microRNAs (miRNAs) in gene regulation?- a)They are translated into proteins
- b)They bind to DNA promoters
- c)They degrade mRNA molecules
- d)They initiate transcription
Correct answer is option 'C'. Can you explain this answer?
Which of the following is a characteristic of microRNAs (miRNAs) in gene regulation?
a)
They are translated into proteins
b)
They bind to DNA promoters
c)
They degrade mRNA molecules
d)
They initiate transcription
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Orion Classes answered |
MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression post-transcriptionally. They typically bind to complementary sequences in mRNA molecules and can lead to their degradation or inhibit their translation into proteins, thereby regulating gene expression.
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