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Gene Expression and Regulation - Part 1 (20 test)
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1. A 6-year-old boy of Scandinavian descent presents with recurrent vomiting, fatigue, and weight Physical examination reveals scleral icterus (yellow whites of eyes) and tenderness over the right upper quadrant of the abdomen. Laboratory studies reveal elevated levels of serum glutamic oxaloacetic transaminase (AST— reflecting liver or heart cell death) and bilirubin (reflecting icterus or jaundice), but no hepatitis A or B viral antigens. A diagnosis of nonviral hepatitis is made, and a family history reveals that the father and his sister suffer from early-onset emphysema, and that the paternal grandmother died from this illness. A suspected diagnosis of α1 antitrypsin (AAT-MIM*104700) deficiency is confirmed by finding the child has only the Z form of AAT on protein electrophoresis, confirmed by DNA sequencing showing homozygous AAG sequences at the 342nd codon (expected to encode lysine) rather than normal GAG (expected to encode glutamine). Which of the following statements about the “genetic code” explain this molecular diagnosis?
- There are 64 codons, each of which can encode several different amino acids.
- There are 64 possible combinations of 3 nucleotides, each combination specifying a specific amino acid or serving as a termination signal.
- There are 16 possible combinations of 2 nucleotides, allowing the first two nucleotides of each codon to specify unique amino acids and rendering the third nucleotide as irrelevant (degenerate).
- Information is stored as sets of trinucleotide repeats called codons, accounting for the evolution of complex genes from simpler ones.
- The 5′ to 3′ sequence of 3-base pair codons within genes is exactly matched by the amino to carboxy sequence of amino acids within the translated protein.
2. A 3-year-old Caucasian boy has grown along the third percentile for age, despite his parents being He also has required treatment for chronic asthma, and his pediatrician notes unusual curvature of his knees and wrists typical of rickets. Testing confirms rickets by x-ray and deficiency of vitamin D, a fat-soluble vitamin that can become deficient with inadequate sunlight or intestinal malabsorption. The latter possibility, together with the asthma and growth delay, suggests a diagnosis of cystic fibrosis (MIM*219700). DNA testing is now very accurate, examining over 100 possible mutations including the 3 bp deletion that removes a codon for phenylalanine (ΔF508). The DNA sequence shown below is the sense strand from a coding region known to be a mutational “hot spot” for a gene. It encodes amino acids 21 to 25. Given the genetic and amino acid codes CCC = proline (P), GCC = alanine (A), TTC = phenylalanine (F), and TAG = stop codon, which of the following sequences is a frameshift mutation that causes termination of the encoded protein 5′-CCC-CCT-AGG-TTC-AGG-3′?
3. A 5-year-old Caucasian girl returns from a mushroom hunt in Northern Michigan and begins vomiting, then shows tremors, extreme anxiety, and finally disorientation—not recognizing her She is taken to the emergency room where jaundice and delirium are noted and followed by liver function tests showing elevated ammonia, liver enzymes, and bilirubin. A toxicologist is called, who suggests poisoning from Amanita phalloides, a mushroom containing the toxin α-amanitin that inhibits RNA polymerase II. The child’s liver failure is most likely due to which of the following?
- Inhibition of tRNA and protein synthesis
- Inhibition of mRNA synthesis
- Inhibition of small RNA synthesis
- Inhibition of ribosomal RNA synthesis
- Inhibition of mitochondrial RNA synthesis
4. A 9-month-old Italian American boy presents with tachypnea and respiratory distress. His physical examination reveals a large spleen and his blood counts reveal severe anemia with targeted red blood cells on smear. A diagnosis of β-thalassemia (MIM*141900) is suggested and analysis of gene structure and expression is As shown in the diagram above Questions 241 to 248, the β-globin gene contains three exons that encode a protein of 150 amino acids, separated by introns of 150 and 750 bp. The β-globin messenger RNA (mRNA) has 5′- and 3′-untranslated regions of 50 nucleotides. Choose the size of the mature β-globin messenger RNA and its amount in this boy with β-thalassemia:
- 1450 bp-normal amount of mRNA
- 700 bp-decreased amount of mRNA
- 550 bp-decreased amount of mRNA
- 500 bp-increased amount of mRNA
- 450 bp-decreased amount of mRNA
5. A “factor” is studied that stimulates a gene controlling differentiation of human immune stem cells into B-cells that fight bacterial infection. Some diseases such as Bruton agammaglobulinemia (MIM*300300) involve an inability to produce B-cells. The factor can hybridize to DNA, is hydrolyzed by alkali treatment, and migrates as a 2 to 30 bp species on electrophoresis. The differentiation gene is not stimulated by the factor if a 10 bp promoter element near the initiation site for transcription is Which of the following factors is most likely?
- A transfer RNA that recognizes a codon within the promoter element
- An mRNA that is translated to produce a stimulatory transcription factor
- A small RNA that binds the promoter and enhances transcription
- A transposon that recognizes the promoter element and inserts to activate the gene
- An RNA catalyst that is essential for mRNA splicing
6. A 3-week-old Caucasian girl has returned for follow-up after her initial newborn metabolic screen showed elevated levels of phenylalanine, causing concern for phenylketonuria (PKU-MIM*261600). The second screen performed at age 2 weeks showed a phenylalanine level of 30 mg/dL with upper limits of normal being 6 mg/dL. Molecular characterization demonstrated a single-base change GT to AT at an intron-exon junction in both of her phenylalanine hydroxylase (PAH) alleles and an unusually large PAH Which of the following most accurately describes these test results?
- The PAH mutation has disrupted RNA catalysis, producing a PKU carrier.
- The PAH mutation has disrupted RNA self-splicing and caused PKU.
- The PAH mutation has disrupted spliceosome activity and caused PKU.
- The PAH mutation has disrupted action of RNA polymerase and caused PKU.
- The PAH mutation has disrupted RNA helicase, producing a PKU carrier.
7. Antibiotics that selectively inhibit bacterial growth exploit differences between bacterial and mammalian Design of a drug that would selectively inhibit bacterial RNA synthesis would target which of the following?
- Spliceosome components
- 3′ ends of tRNA unprotected by caps
- 3′ ends of mRNA unprotected by caps
- 5′ ends of mRNA unprotected by caps
- Poly(A) addition to the 5′ end
8. A 36-year-old female elects to have amniocentesis with her third pregnancy because of “advanced” maternal age—her family history and that of her 38-year-old husband are The fetal chromosomes show a normal number of 46, but one chromosome 21 has a large satellite region. The couple is called back for parental chromosomes and is extremely anxious that their fetus may have Down syndrome. The same enlarged satellite is seen on one chromosome 21 of the father, and silver staining shows this amplified DNA to be part of the nucleolar organizing region (NOR). The counselor explains that these NOR regions are seen on chromosomes 13 and 15 and 21 and 22 (acrocentric chromosomes) and are transcriptionally active in the nucleolus. The molecules associated with these NOR would most likely be which of the following?
- Messenger RNA used to synthesize histone proteins
- Small silencing RNA (siRNA)
- Poly(A) RNA
- Ribosomal RNA
- Transfer RNA
9. Which one of the following statements best describes the synthesis of mammalian messenger RNA (mRNA)?
- There is colinearity of the RNA nucleotides transcribed from a gene and the amino acids encoded by each nucleotide.
- Each mRNA often encodes several different proteins.
- Several different genes may produce identical mRNA molecules.
- The RNA sequence transcribed from a gene is virtually identical to the mRNA that exits from nucleus to cytoplasm.
- Mammalian mRNA undergoes minimal modification during its maturation.
10. A 35-year-old African American male has noted deteriorating skills in activities such as golf and tennis, lately noting difficulties with handwriting. Evaluation reveals poor tandem walking and finger-to-nose coordination, and a peripheral smear shows shrunken and spiny red blood cells called Serum lipoprotein electrophoresis shows very low density lipoproteins (VLDL) and low-density lipoproteins (LDL), suggesting a diagnosis of abetalipoproteinemia (MIM*200100). Which of the following is the best method to demonstrate yield of different apolipoprotein B (apoB) protein sizes through RNA editing?
- Western blot using apoB DNA as probe
- Northern blot using antibody to apoB protein as probe
- Southern blot using the proximal apoB gene segment as probe
- Western blot using apoB cDNA as probe
- Western blot using antibody to the amino-terminal portion of apoB protein
11. A 26-year-old male medical student contracts a skin infection from an elderly patient and notes an expanding circular red lesion on his thigh at dinner that He places a warm washrag on the lesion at bedtime and awakens in early morning feeling hot with shortness of breath. After reluctantly going to the health clinic, he faints during the registration process and awakens in the intensive care unit. An infectious disease specialist tells him he has methicillin-resistant Staphylococcus aureus with toxic shock syndrome (low blood pressure) and adult respiratory distress syndrome (swelling of alveolar membranes with hypoxemia). The attending wishes to use a new antibiotic that acts on the earliest step of protein synthesis. Which of the following steps would most likely be targeted?
- Peptide bond formation
- Loading of the small ribosomal subunit with initiation factors, messenger RNA, and initiation aminoacyl-tRNA
- Sliding of the ribosome three bases forward to read a new codon
- Binding of the small ribosomal subunit to the large ribosomal subunit
- Elongation factors deliver aminoacyl-tRNA to the A site of the small ribosomal subunit
12. A 15-year-old Caucasian adolescent of Scandinavian descent has suffered from mild liver disease thought to be related to receiving parenteral nutrition as a premature infant. Recently she has developed shortness of breath, and has decreased oxygen saturation measured at Emphysema is suspected that with liver disease suggests α1-antitrypsin (AAT) deficiency (MIM*107400), confirmed by protein electrophoresis that shows only mutant protein. Given that normal AAT blocks serum proteases, which of the following is the most likely mechanism for AAT disease?
- Disruption of signal peptide function with accumulation of AAT protein in the Golgi apparatus
- Disruption of signal peptide function with increased amounts of AAT in plasma
- Disruption of AAT protease function
- Decreased targeting of AAT mRNA to smooth ER ribosomes
- Increased targeting of AAT mRNA to rough ER ribosomes
13. A couple request genetic counseling because their first child had severe β-thalassemia (MIM*141900) and expired at age 1 year from graft-versus-host reaction after bone marrow transplant. DNA analysis of the child demonstrated a promoter mutation on one copy of the β-globin gene and a mutation in the middle of exon 2 on the other What is the most likely type of mutation in exon 2 that would lead to β-thalassemia (ie, decreased production of β-globin peptide from both β- globin gene copies), and what is the couple’s recurrence risk for their next child to be affected?
- Deletion of 3 bp, 50%
- Insertion of 1 bp, 25%
- Insertion of 3 bp, 25%
- Missense mutation, 25%
- Silent mutation, virtually zero recurrence risk
14. How many high-energy phosphate-bond equivalents are utilized in the process of activation of amino acids for protein synthesis?
15. The hydrolytic step leading to the release of a polypeptide chain from a ribosome is catalyzed by which of the following?
- Dissociation of ribosomes
- Peptidyl transferase
- Release factors
- Stop codons
16. The sequence of the template DNA strand is 5′-GATATCCATTAGT-GAC-3′. What is the sequence of the RNA produced?
17. Which of the following statements about ribosomes is true?
- They are composed of RNA, DNA, and protein.
- They are composed of three subunits of unequal size.
- They are bound together so tightly they cannot dissociate under physiologic conditions.
- They are found both free in the cytoplasm and bound to membranes.
- They are an integral part of transcription.
18. Guanosine triphosphate (GTP) is required by which of the following steps in protein synthesis?
- Aminoacyl-tRNA synthetase activation of amino acids
- Attachment of ribosomes to endoplasmic reticulum
- Translocation of tRNA-nascent protein complex from A to P sites
- Attachment of mRNA to ribosomes
- Attachment of signal recognition protein to ribosomes
19. A 50-year-old African American male develops cough and fever for 3 days while attending a convention, then returns to his home city for medical Chest x-rays reveal diffuse (interstitial) pneumonia, and the male’s poor oxygen saturation and severe cough mandate hospitalization. His physician calls a hospital in the convention town and hears that over a dozen conventioneers received ER treatment for similar symptoms. The physician suspects mycoplasma or pertussis infection similar to Legionnaires disease and prescribes erythromycin. Erythromycin, azithromycin (Zithromax), and clarithromycin (Biaxin) are macrolide antibiotics that inhibit protein synthesis in certain bacteria by doing which of the following?
- Inhibiting translocation by binding to 50S ribosomal subunits
- Acting as an analogue of mRNA
- Causing premature chain termination
- Inhibiting initiation
- Mimicking mRNA binding
20. An immigrant family from rural Mexico brings their 3-month-old son to the emergency room because of whistling inspiration (stridor) and high The child’s physician is perplexed because the throat examination shows a gray membrane almost occluding the larynx. A senior physician recognizes diphtheria, now rare in immunized populations. The child is intubated, antitoxin is administered, and antibiotic therapy is initiated. Diphtheria toxin is often lethal in unimmunized persons because it does which of the following?
- Inhibits initiation of protein synthesis by preventing the binding of GTP to the 40S ribosomal subunit
- Binds to the signal recognition particle receptor on the cytoplasmic face of the endoplasmic reticulum receptor
- Shuts off signal peptidase
- Blocks elongation of proteins by inactivating elongation factor 2 (EF-2 or translocase)
- Causes deletions of amino acid by speeding up the movement of peptidyl-tRNA from the A site to the P site