This set of Molecular Biology Problems focuses on “Transcriptional Regulation in Eukaryotes is More Complex than in Prokaryotes – 2”.
1. Which of the following is not a target site for repressor molecules?
d) Promoter sites
Explanation: Several distinct types of repression domains have been identified. The functional targets of repressors are also diverse. Repressors can inhibit transcription by interacting with specific activator proteins, with mediator proteins or general transcription factors, and with co-repressors that act by modifying chromatin structure.
2. Which of the following about the enhancers is false?
a) They function in orientation
b) They function as promoter sequences
c) They work as both cis and trans-acting sequences
d) They are tissue specific.
Explanation: Enhancers are sequences that are present in the genome of an organism that help regulate the expression of the gene in coordination with other mediators and factors. They are distinct sequences that lie upstream or downstream of a gene or even on the other homologous chromosome. The can regulate the function of gene even from a distance and are tissue specific in nature.
3. In case of transcription regulation what is the function of enhancer molecules?
a) Helps initiate transcription
b) Transcription elongation
c) Stimulates the rate of transcription
d) mRNA stability enhancement
Explanation: In case of transcription regulation the enhancer molecules stimulates the rate of transcription. They help in the binding of the required mediators thus stimulating correct and fast transcription of the specific gene.
4. Gene imprinting involves ___________
a) DNA methylation
b) DNA phosphorylation
c) DNA glycosylation
d) DNA oxidation
Explanation: Genome imprinting involves the methylation of DNA. It is an epigenetic phenomenon that allows the monoallelic expression of subsets of genes dependent on parental origin.
5. Acetylation of histone increases transcription of gene due to ___________
a) Increase in the DNA-histone interaction
b) It loosens the DNA-histone complex thus making it accessible to RNA polymerase
c) It induces DNA blending which is recognized by RNA polymerase
d) The acetyl groups are recognizable by RNA polymerase
Explanation: Acetylation of histone H3 molecule occurs at the N-terminal tail. The addition of two acetyl group at the two H3 molecules loosens up the higher order of chromatin structure thus helping the RNA polymerase to bind to the respective DNA sequence thus increases transcription of gene.
6. With respect to the methylation of bases which of the following is correct?
a) Protects against the action of S1 nuclease
b) Methyl groups are added to cystine in eukaryotic cells
c) It results in localized conversion of A-DNA to Z-DNA
d) Involved in translation
Explanation: DNA methylation protects against the action of endonucleases. They are added to cytosine residues. Methylation occurs in the DNA bases thus helps in transcription and not translation.
7. Which of the following about enhancer sequence is incorrect?
a) They are required for transcriptional regulation of some genes
b) They can work in both directions
c) They can work when present in any position of the DNA
d) They are not responsible for specificity of tissues
Explanation: Enhancer sequences are partly responsible for specificity of certain tissues. For example, the enhancer that controls the transcription of immunoglobulin is active in lymphocytes, but not in other types cells. Thus, this regulatory sequence is at least partly responsible dor tissue-specific expression of the immunoglobulin genes in the appropriate differentiated cell type.
8. The most commonly observed modification in the histone includes ___________
a) Acetylation of lysine and phosphorylation of serine
b) Acetylation of lysine and phosphorylation of threonine
c) Acetylation of arginine and phosphorylation of threonine
d) Acetylation of arginine and phosphorylation of serine
Explanation: Lysine groups generally undergo acetylation and methylation and serine undergo phosphorylation. They regulate the expression of the gene thus regulating transcription in the genome of an organism.
9. Which of the following about the differences between the prokaryotic and eukaryotic genes are true?
a) Prokaryotic genes are large, polycistronic and contains enhancers
b) Eukaryotic genes are large, polycistronic and contains enhancers
c) Prokaryotic genes are large, monocistronic and contains introns
d) Eukaryotic genes are large, monocistronic and contains introns
Explanation: Prokaryotic genes are polycistronic whereas Eukaryotic genes are monocistronic. Eukaryotic genes contain introns whereas prokaryotic genes do not. Both prokaryotic and eukaryotic genes contain enhancers.
Sanfoundry Global Education & Learning Series – Molecular Biology.
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