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BCMB 412 exam 3
| Question | Answer |
|---|---|
| During the cleavage stage of animal embryogenesis, cells go through multiple rounds of cell division without intervening growth. | True |
| The cleavage stage in animal embryos results in a ball of cells with a fluid-filled interior called a blastula | True |
| Muscles are derived from ectoderm | false, mesoderm |
| Nerves are derived from mesoderm | False, ectoderm |
| Delta is a diffusible signaling protein that activates the Notch receptor protein on target cells. | False, its a transmembrane |
| Notch functions both as a cell-surface receptor protein and as a transcriptional regulator. | True |
| Signaling by Spatzle leads to activation of the Cactus protein | False, causes ubiquitylation of Cactus so it dissociates from Dorsal protein |
| During embryonic development, differentiation of previously similar cells is usually accompanied by divergence in patterns of gene expression | True |
| The sog gene is activated only at the highest concentrations of Dorsal. | False, it has the highest affinity for dorsal so it works at low concentration |
| The Dorsal-binding sites in the sog gene have a higher affinity for Dorsal than those in the twist gene. | True |
| Oskar mRNA is transported to the _______ (posterior)pole of Drosophila oocytes along microtubules by the motor protein _______ (kinesin). | posterior, kinesin |
| Bicoid mRNA is transported to the ____ (anterior) pole of the oocyte along microtubules by the motor protein ______ (dynein) | anterior, dynein |
| .The sequences at the 5’ end of a mature mRNA for the adenovirus hexon protein are transcribed from DNA sequences well separated from the coding sequences of the hexon gene in the adenovirus genome. | true |
| All of the mature mRNAs for late-gene adenovirus proteins have identical 5’ ends. | True |
| The exons of a gene include only the protein-coding sequences. | False, the 5’ leader and 3’ non-coding regions are also exons because they are retained in the mature mRNA. |
| Most introns in human genes are less than 100 bases in length | False, up to 800 kb |
| Conventional cis-splicing can occur only if the two exons are encoded on the same DNA strand. | True |
| Step 1 of the splicing reaction can occur only if the branch point A is correctly base paired as part of an RNA duplex with U2 snRNA. | True |
| The sequence AG is nearly always present at the 3’ end of mRNA introns | True |
| A unique feature of the intron downstream of exon 5 in the Dscam pre-mRNA is the presence of a docking site sequence complementary to “selector sequences” located upstream of each of the 48 alternative exon 6 sequences | True |
| SR proteins are splice repressors that prevent recruitment of spliceosome components to their intronic binding sites. | False |
| An important function of U5 snRNA is to help position the upstream and downstream exons near each other in preparation for the second step of the splicing reaction. | True |
| The levels of Sis-a and Sis-b proteins are higher in female embryos than in male embryos but the levels of Dpn protein are the same in female and male embryos. | True |
| A fruit fly with 2 X chromosomes but four copies of each of the autosomes would be a female. | False ratio of 1:1 in females and 0.5:1 in males |
| Sxl protein functions as a splice site repressor on both Sxl and Tra pre-mRNAs. | True |
| Tra protein binds to both the Tra and Dsx pre-mRNAs and regulates their splicing. | False |
| Assembly of the large and small subunits of eukaryotic ribosomes takes place in the nucleolus. | True |
| Isoacceptor tRNAs are tRNAs that have different anticodon sequences but bind to the same codon. | False |
| Translation and transcription occur simultaneously in eukaryotes but not in prokaryotes. | False |
| All tRNAs have the same three bases at their 3’ ends | True. An enzyme adds CCA to the 3’ end. |
| The differentiation of different types of neurons in the vertebrate neural tube is controlled by a gradient of Sonic Hedgehog (Shh) resulting from Shh secretion by the floorplate cells. | True |
| In Drosophila embryos, the cleavage divisions involve mitosis without accompanying cytokinesis. | True. The 14 cleavage divisions involve mitosis but not cytokinesis. |
| During dorsal-ventral axis determination, Dorsal is present at the highest concentration in nuclei on the dorsal side of the embryo. | False - Doral has highest concentration on the ventral side. |
| The Dorsal-binding sites in the sog gene have a higher affinity for Dorsal than those in the twist gene. | True and more of them |
| Why is the sog gene not expressed in the future mesodermal cells near the ventral midline of Drosophila embryos despite having multiple binding sites for Dorsal in its regulatory DNA? | The transcriptional repressor Snail, which is expressed exclusively in mesodermal cells, binds to sog regulatory DNA and overrides Dorsal, keeping sog expression off in the mesoderm. |
| The sequences at the 5’ end of a mature mRNA for the adenovirus hexon protein are transcribed from DNA sequences well separated from the coding sequences of the hexon gene in the adenovirus genome | True |
| The exons of a gene include only the protein-coding sequences. | False, the 5’ leader and 3’ non-coding regions are also exons because they are retained in the mature mRNA. |
| The only absolutely conserved base in the branchpoint of introns is the A that initiates the first splicing reaction. | False |
| A unique feature of the intron downstream of exon 5 in the Dscam pre-mRNA is the presence of a docking site sequence complementary to “selector sequences” located upstream of each of the 48 alternative exon 6 sequences | True |
| The effect of Sxl protein on Tra pre-mRNA splicing is to truncate the 5’ end of an exon (or, equivalently, extend the 3’ end of an intron). | True |
| SR proteins are splice repressors that prevent recruitment of spliceosome components to their intronic binding sites | False |
| An important function of U5 snRNA is to help position the upstream and downstream exons near each other in preparation for the second step of the splicing reaction. | True |
| Sxl protein functions as a splice site repressor on both Sxl and Tra pre-mRNAs | True |
| Tra protein binds to both the Tra and Dsx pre-mRNAs and regulates their splicing. | False |
| Assembly of the large and small subunits of eukaryotic ribosomes takes place in the nucleolus. | True |
| Synthesis of a mature mRNA for an adenovirus protein would require splicing out a minimum of ______ introns from the pre-mRNA | 3 |
| Which of the following statements about exons and introns in the fly and human genomes is true? | On average, human exons are shorter than fly exons. |
| Which of the following statements about the branch point site of an intron is true? | It is located near the 3’ end of the intron but 5’ to the polyPy tract. |
| 20. In the first step of the splicing reaction, the bond between phosphate and the ______ of the ____ is broken due to nucleophilic attack of the 2’OH of the branch site A. | 3’OH, last (3’-most) nucleotide of the upstream exon |
| The first spliceosome component to bind to the 5’ splice site is: | U1 |
| The first spliceosome component to bind to the branch point site is: | BBP |
| At the end of the splicing reaction, the intron is released as a: | lariat structure in which the branch point A is joined to the 5’ end of the intron through a 2’ O-P bond, in addition to being bonded to its neighboring nucleotides by conventional 5’ O-P and 3’ O-P bonds. |
| The order of release of spliceosome components during the splicing pathway is: | BBP, U2AF, U1, U4 |
| the spliceosome component that binds initially to the 3’ splice site is: | U2AF |
| Where do SR proteins bind during the splicing reaction? | exonic splicing enhancers (ESEs) in the flanking exons. |
| U6 snRNA forms base pairing complexes with which of the following components at some point during the splicing reaction pathway? | U2 snRNA |
| In the second step of the splicing reaction, the 3’ OH of the _____ attacks the sugar-phosphate bond of the 3’ OH of the ______. | 3’-most nucleotide of the upstream exon, 3’-most intron nucleotide |
| What event is thought to create the spliceosome active site and trigger the first catalytic step of the splicing reaction? | Base pairing between the U6 and U2 snRNAs |
| U2 snRNA interacts by base-pairing with which of the following spliceosome components at some point in the splicing pathway? | the branch point site and U6 snRNA |
| The active site of the spliceosome is thought to consist of: | components of the U2 and U6 snRNAs. |
| . Which of the following statements about Sex-lethal (Sxl) protein is not true | Sxl protein functions as a splice site repressor on Sxl pre-mRNA but as a splice site activator on Tra pre-mRNA. |
| Which of the following statements about Tra protein is true? | Tra protein functions to activate a cryptic 3’ splice site on Dsx pre-mRNA. |
| 34. Sxl pre-mRNA is produced in _______ in early embryos and in ________ during and after late embryogenesis. | females only, both sexes |
| Transcription of the Sxl gene in early embryos occurs only if the ratio of Sis-a + Sis-b proteins to Dpn protein is: | 2:1 |
| A good example of “exon-skipped” type alternative splicing is splicing of the pre-mRNA for: | troponin T |
| During the splicing reaction, the 5’ splice site of the intron is bound first by _______, then by _______. | U1 snRNA, U6 snRNA |
| What event is thought to create the spliceosome active site and trigger the first catalytic step of the splicing reaction? | Base pairing between the U6 and U2 snRNAs. |
| Which of the following statements about Sxl promoters is not true? | Pe and Pm are both regulated by dimeric transcription factors constructed from the Sis-a, Sis-b and Dpn proteins. |
| Which part of an intron would the sequence GUAAGU likely represent? | 5’ splice site |
| The Toll receptor is a transmembrane protein ubiquitously distributed throughout the plasma membrane of early Drosophila embryos. | True |
| Mammals have four separate homeotic gene complexes, all of which are involved in establishing cellular identities along the anterior-posterior axis. | true- gene complexes are hoxa, hoxb, hoxc, and hoxd |
| Development of wings and legs in thoracic segments in Drosophila requires high levels of expression of the homeotic protein Antp. | true |
| Misexpression of Drosophila Ubx in all of the cells of the future T2 segment of a Drosophila embryo would likely lead to: | absence of legs and replacement of the wings with halteres in T2. |
| The Twist gene is activated only in the cells nearest to the ventral midline of blastoderm embryos because: | Twist transcription requires very high levels of Dorsal protein, levels present only in ventral cells, because there are only two low-affinity Dorsal binding sites in its upstream regulatory. |
| Hunchback protein is expressed only in the anterior half of Drosophila embryos because: | a and b |
| Which of the following statements about pair-rule genes is true? | all of the above |
| Which of the following statements about homeotic genes is not true? | Homeotic genes are present only in genomes of animals with highly segmented body plans, like arthropods. |
| Why is the sog gene not expressed in the future mesodermal cells near the ventral midline of Drosophila embryos despite having multiple binding sites for Dorsal in its regulatory DNA? | The transcriptional repressor Snail, which is expressed exclusively in mesodermal cells, binds to sog regulatory DNA and overrides Dorsal, keeping sog expression off in the mesoderm. |
| Why is the mesodermal gene Twist not expressed in future neurectoderm cells of Drosophila embryos despite having Dorsal binding sites in its regulatory DNA? | The Dorsal binding sites in Twist regulatory DNA are low-affinity sites that cannot recruit enough Dorsal protein in neuroectoderm cells, where Dorsal nuclear concentration is relatively low, to activate transcription. |
| A mutation that prevents expression of Ubx in the T3 (third thoracic) segment would likely result in flies with: | two pairs of wings but no halteres. |
| The anterior and posterior borders of Eve stripe-2 are set by binding of the _____ and ______ repressors, respectively, to the stripe-2 enhancer. | Giant Kruppel |
| Which of the following statements about lateral inhibition in differentiation of Drosophila neurons and epidermal cells is true? | Binding of Delta to Notch induces cleavage of its cytoplasmic domain, which then translocates into the nucleus and activates target genes. |
| How do the Ubx proteins of Drosophila and brine shrimp differ? | The brine shrimp protein has an anti-repression domain not present in the Drosophila protein. |
| In four-winged insects like the Lepidopterans butterflies and moths, the extra pair of wings (relative to dipterans like Drosophila) can develop because: | The promoters of wing development genes like wingless in Lepidopterans lack binding sites for Ubx. |
| Step 1 of the splicing reaction can occur only if the branch point A is correctly base paired as part of an RNA duplex with U2 snRNA. | false, step 1 involves BBP binding to the branch point |
| The sequence AG is nearly always present at the 3’ end of mRNA introns. | True |
| The only absolutely conserved base in the branchpoint of introns is the A that initiates the first splicing reaction | False |
| An important function of U5 snRNA is to help position the upstream and downstream exons near each other in preparation for the second step of the splicing reaction. | True |
| The levels of Sis-a and Sis-b proteins are higher in female embryos than in male embryos but the levels of Dpn protein are the same in female and male embryos | True |
| Sxl protein functions as a splice site repressor on both Sxl and Tra pre-mRNAs. | True |
| Tra protein binds to both the Tra and Dsx pre-mRNAs and regulates their splicing. | False |
| Which of the following statements about the branch point site of an intron is true? | It is located near the 3’ end of the intron but 5’ to the polyPy tract. |
| In the first step of the splicing reaction, the bond between phosphate and the ______ of the ____ is broken due to nucleophilic attack of the 2’OH of the branch site A. | 3’OH, last (3’-most) nucleotide of the upstream exon |
| The first spliceosome component to bind to the 5’ splice site is: | U1 |
| The order of release of spliceosome components during the splicing pathway is | d. BBP, U2AF, U1, U4 |
| U6 snRNA forms base pairing complexes with which of the following components at some point during the splicing reaction pathway? | f. b, c and d only. |
| In the second step of the splicing reaction, the 3’ OH of the _____ attacks the sugar-phosphate bond of the 3’ OH of the ______. | d. 3’-most nucleotide of the upstream exon, 5’-most nucleotide of the downstream exon |
| What event is thought to create the spliceosome active site and trigger the first catalytic step of the splicing reaction? | Base pairing between the U6 and U2 snRNAs. |
| U2 snRNA interacts by base-pairing with which of the following spliceosome components at some point in the splicing pathway? | the branch point site and U6 snRNA |
| The active site of the spliceosome is thought to consist of: | components of the U2 and U6 snRNAs. |
| Which of the following statements about Sex-lethal (Sxl) protein is not true? | Sxl protein functions as a splice site repressor on Sxl pre-mRNA but as a splice site activator on Tra pre-mRNA. |
| .Which of the following statements about Tra protein is true? | Tra protein functions to activate a cryptic 3’ splice site on Dsx pre-mRNA. |
| During the splicing reaction, the 5’ splice site of the intron is bound first by _______, then by _______. | U1 snRNA, U6 snRNA |
| What event is thought to create the spliceosome active site and trigger the first catalytic step of the splicing reaction? | Base pairing between the U6 and U2 snRNAs. |
| Which of the following statements about Sxl promoters is not true? | Pe and Pm are both regulated by dimeric transcription factors constructed from the Sis-a, Sis-b and Dpn proteins. |
| What reaction takes place in the synthetic center of an amino acyl tRNA synthetase? | A and b |
Created by:
baverwat