Exam 17: Control of Gene Expression in Eukaryotes

A) core promoter
B) enhancer element
C) response element
D) boundary element
E) silencer element

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A) cleavage of RISCs by endonucleases.
B) cleavage of functional mRNA within the cytoplasm.
C) cleavage of pre-mRNA in the nucleus.
D) cutting and processing of double-stranded RNA by Dicer enzymes.
E) cutting and processing of double-stranded RNA by Slicer enzymes.

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A) Transcription of the genes involved in galactose metabolism would occur both in the presence and in the absence of galactose.
B) GAL80 would be able to bind to GAL4, and transcription of the genes involved in galactose metabolism would be repressed.
C) GAL4 would no longer be able to bind to the DNA; thus, transcription of the genes involved in galactose metabolism would occur.
D) GAL80 would no longer be able to stimulate transcription of the genes involved in galactose metabolism.
E) There would be no change in the regulation of galactose metabolism because GAL3 normally binds to GAL80 to cause a conformation change in GAL80.

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A) cleavage of mRNA
B) inhibition of translation
C) posttranslational modification
D) degradation of mRNA
E) transcriptional silencing

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A) production of heat-shock elements.
B) mammalian SV40 virus.
C) lac operon in E. coli.
D) metallothionein gene.
E) None of the answers is correct.

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A) active transcription
B) active translation
C) RNA degradation
D) transcriptional stalling
E) DNA hypermethylation

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C

A) core promoter
B) general transcription factors
C) TATA box
D) RNA polymerase
E) enhancer

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The stability of eukaryotic messenger RNAs (mRNAs) is influenced by several factors that can affect their degradation rates and, consequently, the level of gene expression. Four key factors that influence the stability of eukaryotic mRNAs are: 1. **5' Cap Structure**: The 5' end of eukaryotic mRNAs is modified with a 7-methylguanosine cap, which is essential for mRNA stability. This cap structure protects the mRNA from exonucleases that degrade RNA from the 5' end. It also plays a role in the initiation of translation and the export of mRNA from the nucleus to the cytoplasm. 2. **3' Poly(A) Tail**: The 3' end of eukaryotic mRNAs typically has a polyadenylate (poly(A)) tail, which is a string of adenine nucleotides. The length of the poly(A) tail influences mRNA stability, with longer tails generally conferring greater stability. The poly(A) tail also interacts with poly(A)-binding proteins (PABPs) that protect the mRNA from degradation and assist in the regulation of translation. 3. **mRNA Sequence Elements**: Specific sequence elements within the mRNA itself can influence its stability. These include AU-rich elements (AREs) and GU-rich elements, which are often found in the 3' untranslated region (UTR) of the mRNA. These elements can be recognized by specific RNA-binding proteins that either destabilize or stabilize the mRNA. For example, AREs are known to target mRNAs for rapid degradation. 4. **RNA-Binding Proteins**: The interaction of mRNAs with RNA-binding proteins (RBPs) can significantly affect their stability. RBPs can bind to specific sequences or structures in the mRNA and either protect it from degradation or target it for rapid turnover. Some RBPs stabilize mRNAs by competing with or blocking the access of decay enzymes, while others recruit components of the degradation machinery to the mRNA. These factors work in concert to finely tune the half-life of each mRNA, thereby controlling the levels of protein synthesis within the cell. The balance between mRNA synthesis and degradation is crucial for proper cellular function and response to environmental changes.

A) at the 5' end with the removal of the poly(A) tail
B) at the 5' end with the removal of the methyl cap
C) at the 3' end with the removal of the poly(A) tail
D) at the 3' end with the removal of the methyl cap
E) Removal from either end is equally likely.

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A) siRNAs and proteins.
B) miRNAs and proteins.
C) RISCs and mRNAs.
D) methyl groups and histone proteins.
E) DNA, histone proteins, and mRNAs.

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Gene regulation through the modification...

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A) becoming transcriptionally active.
B) becoming more condensed.
C) binding to the single-strand binding proteins.
D) destabilizing and transcriptionally inactive.
E) becoming highly methylated by a methylase.

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A) In a general sense, highly condensed DNA bound with histone proteins represses gene expression.
B) Acetylation involves the addition of acetyl groups to histone proteins, and it usually results in repression of transcription.
C) Addition of methyl groups to the tails of histone proteins always results in activation of transcription.
D) Histone code refers to the modification that takes place on the globular domain of the octamer histone core.
E) Phosphorylation of cytosines generally leads to increase in transcription..

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A) changes in chromatin structure
B) changes in transcriptional regulator proteins
C) assembly of the basal transcription apparatus
D) factors that increase RNA polymerase stalling
E) association of transcriptional coactivators

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D

A) DNAse I.
B) ribozymes.
C) heat-shock proteins.
D) silencers.
E) ribonucleases.

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A) There is a mutation in the gene that encodes the Dicer enzyme that makes it nonfunctional.
B) There is a mutation that results in an overexpression of siRNAs.
C) There is a mutation in the gene that encodes the Slicer enzyme that allows it to cut RNA more efficiently.
D) There is a mutation in a gene that encodes an acetylase enzyme that prevents histone acetylation.
E) There is a mutation in a gene that encodes an enzyme that selects the correct splice site for alternative splicing.

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A) insulator.
B) repressor.
C) enhancer.
D) coactivator.
E) mediator.

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1. Post-transcriptional gene silencing: ...

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