Block 1 Gene Expression

1.

Chromatin remodeling occurs by covalent changes to nucleosomal proteins. What other covalent change can contribute to altered patterns of general gene expression?

A.

Proteolysis of general transcription factors
B.

Myristoylation of CREB-1 transcription factor
C.

Methylation of DNA cytosines
D.

Hydroxylation of TATA box purines
E.

Glycosylation of RNA polymerase II

Correct Answer
C. Methylation of DNA cytosines

Explanation
Methylation of DNA cytosines can contribute to altered patterns of general gene expression. Methylation is a covalent modification of DNA where a methyl group is added to the cytosine base. This modification can affect gene expression by blocking the binding of transcription factors to the DNA, preventing the initiation of transcription. Methylation patterns can be heritable and can play a role in regulating gene expression during development and in response to environmental factors.

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2.

How is the process of ubiquitination of some cellular proteins associated with levels of functional gene expression?

A.

It determines the half-life of functional proteins, after expression
B.

It determines the rate of mRNA translation in the cytosol
C.

It determines the rate that an mRNA traverses the nuclear pore
D.

It determines the Km and Vmax of enzymes
E.

It determines a protein's membrane affinity

Correct Answer
A. It determines the half-life of functional proteins, after expression

Explanation
Ubiquitination is a process where ubiquitin molecules are attached to proteins, marking them for degradation by the proteasome. This process plays a crucial role in regulating protein levels and controlling their half-life. By ubiquitinating proteins, the cell can target them for degradation, thus reducing their abundance and controlling their functional expression. Therefore, the process of ubiquitination is associated with the half-life of functional proteins after they have been expressed.

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3.

The trp operon is associated with biosynthesis of tryptophan. In cases where there is plenty of tryptophan in the environment, what happens at the level of the promoter of the trp operon?

A.

The CRP protein binds to the CAP site
B.

The repressor binds to tryptophan in is released from its binding to the operator
C.

The activator binds and facilitates RNA polymerase binding to the promoter
D.

The attenuation of translation is relieved by the slower processivity of RNA polymerase
E.

The amount of trp repressor protein is decreased by regulation of its own transcription

Correct Answer
D. The attenuation of translation is relieved by the slower processivity of RNA polymerase

Explanation
In cases where there is plenty of tryptophan in the environment, the trp operon is not needed for the biosynthesis of tryptophan. The trp repressor protein, which normally binds to the operator and prevents transcription, is decreased by regulation of its own transcription. This allows RNA polymerase to bind to the promoter and transcribe the trp operon. However, the attenuation of translation is relieved by the slower processivity of RNA polymerase. This means that the RNA polymerase pauses and allows the formation of a hairpin structure in the mRNA, which prevents the formation of the transcription termination hairpin. As a result, transcription continues and the trp operon is transcribed.

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4.

Analysis of a patient’s blood proteins shows that all the proteins needed for blood clotting are present. However, on of the proteins is at a much lower concentration than in normal subjects. Only 10 % of the normal subjects’ protein X concentration is present. What is the MOST LIKELY explanation?

A.

The rate of transcription of the gene encoding protein X is only 10 % of that of normal subjects.
B.

The protein degradation rate of this protein X is at a much faster rate in the patient.
C.

The post-translational modifications to this protein occur only to the extent of 10 % of a normal subject.
D.

The Ribosomal machinery of this individual is compromised and inefficient in translating the mRNA encoding protein X
E.

The blood test is very likely to be in error.

Correct Answer
A. The rate of transcription of the gene encoding protein X is only 10 % of that of normal subjects.

Explanation
The most likely explanation is that the rate of transcription of the gene encoding protein X is only 10% of that of normal subjects. This means that the gene responsible for producing protein X is not being transcribed at the same rate as in normal individuals, resulting in a lower concentration of the protein. This could be due to a mutation or malfunction in the regulatory mechanisms that control gene expression.

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5.

The tryptophan operon of prokaryotes is optimally activated when the growth media contains which nutritional mixture described below?

A.

High tryptophan, low glucose
B.

High tryptophan, high glucose
C.

Low tryptophan, glucose doesn’t matter
D.

Low tryptophan, high glucose
E.

Low tryptophan, low glucose

Correct Answer
C. Low tryptophan, glucose doesn’t matter

Explanation
The tryptophan operon is a group of genes that are involved in the synthesis of tryptophan, an essential amino acid. The operon is regulated by a repressor protein that binds to the operator region of the operon. When tryptophan levels are low, the repressor is unable to bind to the operator, allowing for transcription and synthesis of tryptophan. In this case, the presence or absence of glucose does not affect the activation of the operon. Therefore, the optimal condition for activation of the tryptophan operon is when tryptophan levels are low, regardless of the presence or absence of glucose.

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6.

The control of gene expression for particular proteins is at the level of transcript stability. What is one example of a gene which is controlled primarily by the rate of hydrolysis of mRNA transcripts?

A.

The insulin gene
B.

The glucose transporter gene, GLUT4
C.

The transferrin receptor gene
D.

The dystrophin gene
E.

The retinoblastoma gene

Correct Answer
C. The transferrin receptor gene

Explanation
The correct answer is the transferrin receptor gene. This gene is primarily controlled by the rate of hydrolysis of mRNA transcripts. This means that the stability of the mRNA transcripts for the transferrin receptor gene determines the level of expression of this gene. If the mRNA transcripts are rapidly degraded, the gene will be expressed at a lower level, whereas if the mRNA transcripts are stable, the gene will be expressed at a higher level.

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7.

The action of transcription factors in control many eukaryotic genes include one transcription factor which binds to the TATAA sequence, the “TATA box”. Which is a true statement concerning this transcription factor?

A.

It is called the sterol-receptor binding protein (SRBP)
B.

It is one of several general transcription factors
C.

It binds DNA by intercalation between DNA bases
D.

It recognizes DNA in the enhancer region
E.

It causes RNA polymerase I binding to the promoter region

Correct Answer
B. It is one of several general transcription factors

Explanation
The correct answer states that the transcription factor that binds to the TATAA sequence is one of several general transcription factors. This means that there are multiple transcription factors involved in the regulation of gene expression, and this particular transcription factor is one of them. It does not specify any other characteristics or functions of the transcription factor.

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8.

One mechanism of bacterial antibiotic resistance involves the destruction of a covalent bond in the structure of drugs such as penicillin. What do bacteria which are susceptible to beta-lactam drugs lack which results in their demise?

A.

An extracellular matrix glycoprotein
B.

A lipid which is susceptible to lipase action
C.

An enzyme which cleaves the beta-lactam ring
D.

A protein complex called the proteosome
E.

A protein which lacks any alpha helical structure

Correct Answer
C. An enzyme which cleaves the beta-lactam ring

Explanation
Bacteria that are susceptible to beta-lactam drugs lack an enzyme that is responsible for cleaving the beta-lactam ring in the structure of the drugs. This ring is essential for the drugs' antibacterial activity. Without this enzyme, the drugs are able to effectively target and inhibit the growth of the bacteria. Therefore, the absence of this enzyme in susceptible bacteria leads to their demise when exposed to beta-lactam drugs.

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