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Gene Expression and Regulation - Part 2 (19 test)
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1. Aminoacyl-tRNA synthetases must be capable of recognizing which of the following?
- A specific tRNA and a specific amino acid
- A specific rRNA and a specific amino acid
- A specific tRNA and the 40S ribosomal subunit
- A specific amino acid and the 40S ribosomal subunit
- A specific amino acid and the 60S ribosomal subunit
2. Ribosomes similar to those of bacteria are found in which of the following?
- Cardiac muscle cytoplasm
- Liver endoplasmic reticulum
- Neuronal cytoplasm
- Pancreatic mitochondria
- Plant nuclei
3. Endogenous insulin is ineffective in type 2 diabetes mellitus (MIM*222100), leading to high blood glucose levels (hyperglycemia) with gradual effects on blood vessels in eye, kidney, and skin. Pregnant women with diabetes mellitus present high glucose loads to their fetus; this stimulates production of fetal insulin (hyperinsulinemia) and causes rapid fetal growth with large birth weight (macrosomia). The stimulation of fetal growth by insulin may be correlated with its effect on gene expression, which is which of the following?
- Stimulation of mRNA production by enhancing 5′ capping
- Acceleration of protein synthesis by phosphorylating initiation inhibitors
- Acceleration of protein synthesis by phosphorylating the 40S ribosomal subunit
- Acceleration of protein synthesis by phosphorylating proteinase K
- Stimulation of mRNA production by enhancing RNA splicing
4. Which of the following eukaryotic promoter/regulatory elements has the most variable position with respect to the start site of transcription?
- Downstream promoter element (DPE)
- Initiator sequence
- TATA box
5. Which of the following is required for certain types of eucaryotic protein synthesis, but not for prokaryotic protein synthesis?
- Messenger RNA
- Ribosomal RNA
- Peptidyl transferase
- Signal recognition particle
6. A 26-year-old black African American suffers vision loss after hitting his head while playing Ophthalmologic evaluation reveals detachment of the retina that seems unusual for such mild trauma, and further medical history notes that the male has lax joints, tall and thin build, and chronic joint pain after exercise. The family history is further revealing in that several individuals have had arthritis and detached retina. The symptoms and history suggest a diagnosis of Stickler syndrome (MIM*108300), a collagen disease that results in lax joints, arthritis, and retinal detachments. The locus for Stickler syndrome has been mapped near that for type II collagen on chromosome 12, and mutations in the COL2A1 gene have been described in Stickler syndrome. The family became interested in molecular diagnosis to distinguish normal from mildly affected individuals. Which of the following results would be expected in an individual with a promoter mutation at one COL2A1 gene locus?
- Western blotting detects no type II collagen chains.
- Southern blotting using intronic restriction sites yields normal restriction fragment sizes.
- Reverse transcriptase-polymerase chain reaction (RT-PCR) detects one-half normal amounts of COL2A1 mRNA in affected individuals.
- Fluorescent in situ hybridization (FISH) analysis using a COL2A1 probe detects signals on only one chromosome 12.
- DNA sequencing reveals a single nucleotide difference between homologous COL2A1 exons.
7. Gyrate atrophy (MIM*258870) is a rare autosomal recessive genetic disorder caused by a deficiency of ornithine aminotransferase. Affected individuals experience progressive chorioretinal degeneration with vision and neurologic The gene for ornithine aminotransferase has been cloned, its structure has been determined, and mutations in affected individuals have been extensively studied. Which of the following mutations best fits with test results showing normal Southern blots with probes from all ornithine aminotransferase exons but absent enzymatic activity?
- Duplication of entire gene
- Two-kb deletion in coding region of gene
- Two-kb insertion in coding region of gene
- Deletion of entire gene
- Missense mutation
8. A 1-year-old Caucasian girl who has been treated for scoliosis and clubfoot is noted to be developmentally delayed with no walking and no speech. Examination reveals increased subcutaneous tissue in her face that causes a coarse appearance, enlarged liver and spleen, scoliosis with a posterior spinal prominence called a gibbus, and increased body hair (hirsutism). A diagnosis of Hurler syndrome (MIM*252800) is considered, and analysis of her white blood cells shows the characteristic deficiency of L-iduronidase. Exogenous L-iduronidase can be taken up by deficient cells via a targeting signal that directs the enzyme to its normal lysosomal location. Which of the following therapeutic strategies is the most realistic and efficient mode of therapy?
- Germ-line gene therapy
- Heterologous bone marrow transplant
- Infection with a disabled adenovirus vector that carries the L-iduronidase gene
- Injection with L-iduronidase purified from human liver
- Autologous bone marrow transplant after transfection with a virus carrying the L-iduronidase gene
9. It is now recognized that all cancers involve genetic changes, even though few are hereditary. An early example was the discovery of a Philadelphia chromosome (terminal deletion of chromosome 22) in leucocytes from patients with chronic myeloid leukemia (MIM*608232). Later work demonstrated that the deleted material was in fact translocated to the terminus of chromosome 9, being an example of a balanced translocation between 9 and Of the following results, which would be the most diagnostic of the 9;22 translocation in chronic myeloid leukemia?
- All chromosome 22 genes show increased incorporation of labeled acetate into histones of chromatin regions.
- A particular gene near the terminus of chromosome 22 shows altered DNA restriction endonuclease patterns.
- The pattern of small RNA “decoration” along leukemic chromatin is changed.
- Increased transcription of mRNA from genes near the terminus for chromosome 9.
- Decreased transcription of mRNA from all loci on the chromosome 22 long arm.
10. A 14-year-old Caucasian adolescent of Ashkenazi Jewish descent is evaluated for fatigue and aching legs at night that had been attributed to “growing pains.” Examination revealed a palpable spleen (splenomegaly because the spleen is not normally palpated at this age). His white blood cells showed the typical foamy appearance of cytoplasm due to lipid accumulation in Gaucher disease (MIM*231000). Gaucher disease was considered, and blood obtained for DNA testing, examining the gene for glucocerebrosidase enzyme that, when deficient, causes accumulation of complex lipids in white cells, brain, liver, and spleen. A homozygous glucocerebrosidase gene mutation was found that changed the mRNA sequence of codon 93 from UAC to the UAA depicted in the table below. Which of the following best describes this result?
- Missense mutation that may interfere with glucocerebrosidase function and could be diagnostic of Gaucher disease
- Silent mutation that should not interfere with glucocerebrosidase function and is not diagnostic of Gaucher disease
- Nonsense mutation that produces a truncated, nonfunctional glucocerebrosidase polypeptide and is diagnostic of Gaucher disease
- Suppressor mutation that interferes with glucocerebrosidase mRNA transcription and is diagnostic of Gaucher disease
- Frameshift mutation that produces a nonfunctional glucocerebrosidase and is diagnostic of Gaucher disease
11. A 3-month-old Caucasian boy fails to grow and has very low muscle tone with strange “kinky” A diagnosis of Menkes kinky hair syndrome (MIM*309400) is made by showing deficient copper in fibroblasts. A likely candidate gene encoding an ATP-dependent copper transporter protein is known, and antibodies to this protein are available. Experimental analysis of the patient’s fibroblast DNA is performed to see if a pathologic mutation can be found, thus confirming the copper transport gene as the cause of Menkes disease. The table below shows a partial DNA sequence from the transporter coding strand as amplified by PCR; the amplified sequence is from a region where a TATA box has been located.
Which of the following experimental results would be the most compatible with a pathologic mutation in the transporter gene
- Usual band of usual intensity on Northern and Western blots
- Absent bands on Northern and Western blots
- Usual band plus a second band of lower size on Northern blot, usual band on Western blot
- Usual band on Northern blot, band of unusual size and reduced intensity on Western blot
- Two unusual bands on Northern blot, usual bands on Western blot
12. Lipoproteins transport lipids from intestine and liver, where they are absorbed and metabolized to peripheral tissues via the They contain core proteins (apo proteins) that bind various types of lipids, thus producing lipoprotein complexes of varying densities—very low density lipoproteins (VLDL), low- density lipoproteins (LDL), and high-density lipoproteins (HDL) after plasma lipoprotein electrophoresis. A disorder called abetalipoproteinemia (MIM*200100) was distinguished by its deficiency of the bands for very low density lipoproteins (VLDL) and low-density lipoproteins (LDL) after plasma electrophoresis. Affected patients have ataxia (wide gait, incoordination), retinopathy (retinal degeneration with blindness), and myopathy (muscle weakness). VLDL and LDL contain the same apoB core protein, their different densities produced by association with different lipids, and apoB became good candidate for mutation in the disorder. Initial characterization of the apoB gene together with its mRNA and protein products demonstrated identical mRNA sizes in all tissues. Western blotting using antibody specific for the amino-terminus of apoB protein showed a 100-kDa species in liver and a 48-kDa species in intestine, as did antibody specific for the C-terminus of the 48-kDa intestinal protein. Molecular study of a patient with abetalipoproteinemia showed normal mRNA sizes, but 100-kDa peptide species were identified in both liver and intestine using the amino- or carboxy-terminus antibody probes. Which of the following processes is most likely deficient in this patient with apobetalipoproteinemia?
- RNA splicing
- DNA amplification
- Transcription initiation
- Transcription factor phosphorylation
- RNA editing
13. During the analyses described in Question 226, another patient with abetalipoproteinemia was found to have negligible amounts of apoB protein in either liver or intestine. Analysis of the patient’s DNA and RNA would most likely yield which of the following results?
- Substitution of the last base of a codon near the middle of the first apoB exon
- Insertion of two bases near the apoB amino-terminus
- Transversion producing a nonsense mutation within the first apoB intron
- Transition affecting the 30th base of the first apoB intron
- Base substitution changing glycine for alanine near the apoB carboxyl-terminus
14. Part of the triplet genetic code involving mRNA codon triplets that start with U is shown below. Using the portion of the genetic code shown, which of the following mutations in the 3′ to 5′ DNA template segments corresponds to a nonsense mutation?
- ACGACGACG to ACAAACACG
- AGGAATATG to AGGAATATT
- AGAATAACA to AAAATAACA
- AAAATGAGC to AAAATAAGC
- AACAACAAC to AACAAGAAC
15. The lactose operon is negatively controlled by the lactose repressor and positively controlled by which of the following?
- Increased concentrations of glucose and cyclic AMP (cAMP)
- Decreased concentrations of glucose and cAMP
- Increased concentrations of glucose, decreased concentration of cAMP
- Decreased concentrations of glucose, increased concentration of cAMP
- Increased concentrations of glucose and adenosine triphosphate (ATP)
16. Which of the following regulators are said to act in “cis?”
- The lac repressor and the lac operator
- The lac operator and mammalian transcription factors
- The lac operator and mammalian enhancers
- Mammalian transcription factors and enhancers
- The lac repressor and mammalian transcription factors
17. The proopiomelanocortin (POMC-MIM*176830) gene encodes several regulatory proteins that affect pituitary function. Children with severe brain defects such as holoprosencephaly (MIM*157170) often have abnormalities in the hypothalamic-pituitary In different brain regions, proteins encoded by this gene have different carboxy-terminal peptides. Which of the following best explains the regulatory mechanism?
- POMC transcription is regulated by different factors in different brain regions.
- POMC translation elongation is regulated by different factors in different brain regions.
- POMC transcription has different enhancers in different brain regions.
- POMC protein undergoes different protein processing in different brain regions.
- POMC protein forms different allosteric complexes in different brain regions.
18. A 3-year-old Chinese boy has severe anemia with prominence of the forehead (frontal bossing) and The red cell hemoglobin concentration is dramatically decreased, and it contains only β-globin chains with virtual deficiency of α-globin chains. Which of the following mechanisms is the most likely explanation?
- A transcription factor regulating the α-globin gene is mutated.
- A regulatory sequence element has been mutated adjacent to an α-globin gene.
- A transcription factor regulating the β-globin gene is mutated.
- A transcription factor regulating the α- and β-globin genes is deficient.
- A deletion has occurred surrounding an α-globin gene.
19. A mutation that results in a valine replacement for glutamic acid at position 6 of the β chain of hemoglobin S hinders normal hemoglobin function and results in sickle cell anemia (MIM*602903) when the patient is homozygous for this mutation. This is an example of which of the following types of mutation?