Molecular Cell Biology - Problem Drill 10: Gene Expression in Eukaryotes

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1 Molecular Cell Biology - Problem Drill 10: Gene Expression in Eukaryotes Question No. 1 of Which of the following statements about gene expression control in eukaryotes is correct? Question #1 (A) In prokaryotes, the control of gene expression includes: Transcriptional Control, proteins secretion control and mrna stability control. (B) In prokaryotes, the control of gene expression includes: Transcriptional Control, mrna export control and mrna stability control. (C) mrna stability or longevity plays no role in the control of gene expression. (D) DNA stability or longevity plays a role in the control of gene expression. In prokaryotes, the control of gene expression includes: Transcriptional Control, mrna export control and mrna stability control. B. Correct! In prokaryotes, the control of gene expression includes: Transcriptional Control, mrna export control and mrna stability control. mrna stability or longevity plays a role in the control of gene expression. mrna stability or longevity plays a role in the control of gene expression. A eukaryotic gene is transcribed in nucleus, which is under the transcriptional control. Then the pre-mrna undergoes RNA processing and mrna export, which belongs to post-transcriptional control. When mrna is translated into protein, it is under the translational control. The newly synthesized protein is modified and sorted into different compartment of the cell for proper function, which is under the post-translational control.

2 Question No. 2 of Which of the following statements about the regulation of gene expression at the level of mrna is correct? Question #2 (A) Promoter, enhancer, and mrna splicing normally involve the initiation step of transcription. (B) Promoter, mrna splicing and transcription factors normally involve the initiation step of transcription. (C) Post-Transcriptional Control includes pre-mrna splicing, polyadenylation, capping, mrna sequestration and mrna export and finally mrna stability and availability for translation. (D) Post-Transcriptional Control includes pre-mrna splicing, mrna sequestration and mrna export and finally mrna stability and availability for translation. Promoter, enhancer, and transcription factors, normally involve the initiation step of transcription. Promoter, enhancer, and transcription factors, normally involve the initiation step of transcription. C. Correct! Post-Transcriptional Control includes pre-mrna splicing, polyadenylation, capping, mrna sequestration and mrna export and finally mrna stability and availability for translation. Post-Transcriptional Control includes pre-mrna splicing, polyadenylation, capping, mrna sequestration and mrna export and finally mrna stability and availability for translation. The control at mrna level includes transcriptional control and post-transcriptional control. Transcriptional control is coordinated by promoter, enhancer, and transcription factors, normally involve the initiation; polyadenylation and capping; mrna sequestration and mrna export; mrna stability and availability for translation.

3 Question No. 3 of Which of the following statements about basal transcription factors is correct? Question #3 (A) Most contain a motif to bind DNA (DNA binding domain). (B) There are three types of DNA binding motifs: Zinc-finger, Valine-zipper and Helix-loop-helix (HLH). (C) There are three types of DNA binding motifs: Zinc-finger, Leucine-zipper and Helix-loop-helix (HLH). (D) Zinc-finger is a repetitive four Cysteine repeat which forms a finger structure. All contain a motif to bind DNA (DNA binding domain). There are three types of DNA binding motifs: Zinc-finger, Leucine-zipper and Helixloop-helix (HLH). C. Correct! There are three types of DNA binding motifs: Zinc-finger, Leucine-zipper and Helixloop-helix (HLH). Zinc-finger is a repetitive two cystein, two histidin that bind a Zn which forms a finger structure. Common feature of transcription factors is that they all contain a motif to bind DNA called DNA-binding domain. There are three types of DNA binding motifs: (1) Zinc-finger: repetitive two cystein and two histidine to bind a Zn, form a finger structure. (2) Leucine-zipper: leucine residue at every other turn of helix, 7 amino acid apart. (3) Helix-loop-helix (HLH): homeodomain, contain many basic amino acid, also called basic HLH (bhlh).

4 Question No. 4 of Which of the following statements about transcription initiation is correct? Question #4 (A) Eukaryotic RNA polymerase itself does not bind to DNA; therefore the Basal TFs are required for initiation. (B) Eukaryotic RNA polymerase binds directly to DNA. (C) Basal TFs are not required for initiation. (D) Transcription initiation involves the following steps: First TBP binds to the TATA box, then TFIIA followed by TFIIB joins initiation complex and then RNA polymerase binds. A. Correct! Eukaryotic RNA polymerase itself does not bind to DNA; therefore the Basal TFs are required for initiation. Eukaryotic RNA polymerase itself does not bind to DNA; therefore the Basal TFs are required for initiation. Basal TFs are required for initiation. Transcription initiation involves the following steps: First TFIID and TBP binds to the TATA box, then TFIIA followed by TFIIB joins initiation complex and then RNA polymerase binds. Steps of transcription initiation involving basal transcription factors are: First TFIID and TBP binds to the TATA box in the promoter region. Then TFIIA joins initiation complex, TFIIB joins initiation complex. TFIIF binds RNA polymerase, RNA pol II - THIIF complex binds initiation complex on DNA, then the transcription begins.

5 Question No. 5 of Which of the following statements about intron splicing is correct? Question #5 (A) Spliceosome is made up of snrna. (B) In alternative splicing, introns are spliced out from a single position and this can cause many isoforms for certain proteins. (C) Introns can be removed by self-splicing such as those in rrna genes and mitochondrial mrna genes, and spliceosome mediated splicing such as those in nuclear mrna genes. (D) Introns are removed by spliceosome mediated splicing. Spliceosome contains both snrna and protein. In alternative splicing, introns are spliced out at different positions, which cause many isoforms for certain proteins. C. Correct! Introns can be removed by self-splicing such as those in rrna genes and mitochondrial mrna genes, and spliceosome mediated splicing such as those in nuclear mrna genes. Introns can be removed by self-splicing such as those in rrna genes and mitochondrial mrna genes, and spliceosome mediated splicing such as those in nuclear mrna genes. After transcription, Post-Transcriptional control plays an important role. First step is splicing which is a process to remove introns from RNA. There are three types of introns, group I and group II introns are found in rrna genes and mitochondrial mrna genes, these are self-spliced, no protein factors required. The third class is pre-mrna introns which are found in nuclear mrna genes, and require spliceosome to remove. Pre-mRNA splicing depends on a Conserved sequence around the intron/exon boundary, notice the GU-AG sequence is 100% conserved in the exonintron boundary. This splicing requires spliceosome, which contains both snrna and protein.

6 Question No. 6 of Which of the following statements about the role 5 capping has in the regulation of gene expression is correct? Question #6 (A) Most mrna is capped at 5 end. (B) Capping at the 5 end protects mrna from export out of the nucleus. (C) Capping at the 5 end protects mrna from nuclease and increases its stability. (D) Capping at the 5 end allows RNA polymerase to bind to mrna and initiate translation. All mrna is capped at 5 end. Capping at the 5 end protects mrna from nuclease and increases its stability. C. Correct! Capping at the 5 end protects mrna from nuclease and increases its stability. Capping at the 5 end allows ribosomes to bind to mrna and initiate translation. Another important post-transcriptional control is 5 capping. All mrna is capped at 5 end. This protects mrna from nuclease and increases its stability. 5 caps also allow ribosome to bind to mrna and initiate translation.

7 Question No. 7 of Which of the following statements about mrna stability and availability is correct? Question #7 (A) Once the mrna gets out of nucleus, they are translated immediately. (B) Once the mrna gets out of nucleus, they may be translated immediately, or they may be degraded. (C) mirna binds to mrna and leads to mrna degradation. (D) sirna: binds to mrna in cytoplasm, inhibit translation. Once the mrna gets out of nucleus, they may be translated immediately, or they may be degraded. B. Correct! Once the mrna gets out of nucleus, they may be translated immediately, or they may be degraded. mirna: binds to mrna in cytoplasm, inhibit translation. sirna: binds to mrna and leads to mrna degradation. Once the mrna gets out of nucleus, they may be translated immediately, or they may be inhibited by mirna or degraded by sirna. mirna binds to mrna in cytoplasm, inhibit translation; sirna: binds to mrna and leads to mrna degradation.

8 Question No. 8 of Which of the following statements about Cap-independent Translation Initiation is correct? Question #8 (A) Mediated by IRES sequence, which is close to AUG. (B) Mediated by IRES sequence, which is distant to AUG. (C) Mostly used by normal eukaryotic cells. (D) Mostly used by normal eukaryotic cells once they are infected by bacteria. A. Correct! Mediated by IRES sequence, which is close to AUG. Mediated by IRES sequence, which is close to AUG. Mostly adopted by virus to escape the host shut down. Mostly adopted by virus to escape the host shut down. A second type of translation initiation is cap-independent, which is mediated by IRES sequence located close to AUG. IRES direct the general initiation factors directly to AUG, and initiate translation. This is mostly adopted by virus to escape the host shut down.

9 Question No. 9 of Which of the following statements about upstream open reading frames is correct? Question #9 (A) Inhibit main open reading frame by its AUG which is upstream of the main ORF AUG, has the priority to attract the scanning initiation complex. (B) Enhances the main open reading frame by its AUG which is upstream of the main ORF AUG. (C) The main open reading frame can be initiated by re-initiation. (D) The main open reading frame can be initiated by leaky scanning. A. Correct! Inhibit main open reading frame by its AUG which is upstream of the main ORF AUG, has the priority to attract the scanning initiation complex. Inhibit main open reading frame by its AUG which is upstream of the main ORF AUG, has the priority to attract the scanning initiation complex. The main open reading frame can be initiated by two mechanisms: re-initiation and leaky scanning. The main open reading frame can be initiated by two mechanisms: re-initiation and leaky scanning. uorf stands for upstream open reading frame. They are short open reading frame upstream of main ORF AUG. They inhibit main ORF by its own AUG which is upstream of the main ORF AUG, has the priority to attract the scanning initiation complex. The uorf peptide can also inhibit translation of main ORF by occupying ribosomes. The main ORF can be initiated by two mechanisms: re-initiation and leaky scanning.

10 Question No. 10 of Which of the following statements about the 3 Untranslated Region is correct? Question #10 (A) 3 UTR binds mirna and other proteins for translation initiation. (B) 3 UTR binds mirna and other proteins for translation inhibition. (C) The longer the poly A, the more deficient the translation. (D) The shorter the poly A, the more efficient translation. 3 UTR binds mirna and other proteins for translation inhibition. B. Correct! 3 UTR binds mirna and other proteins for translation inhibition. The longer poly A, the more efficient translation. The longer poly A, the more efficient translation. 3 UTR stands for 3 Untranslated Region. It binds mirna and other proteins for translation inhibition. Poly A binds a protein which can interact with a translation initiation factor; folds back the mrna molecule, and promote translation. The longer poly A, the more efficient translation.