Biochem NBME questions
c. Multifactorial inheritance
A 2-year-old boy has a unilateral cleft lip and cleft palate. He has no other malformations and is otherwise healthy. He has no family history of birth defects. His parents are not related. Which of the following genetic mechanisms is most likely to have caused these congenital abnormalities? Select one: a. Autosomal recessive inheritance b. Chromosome deletion c. Multifactorial inheritance d. Autosomal dominant inheritance e. Chromosome aneuploidy f. Mitochondrial DNA mutation g. X-linked recessive inheritance
e. Maternal germline mosaicism
A 23-year-old woman (individual ||-1 in the pedigree) seeks genetic counseling because her brother has Duchenne muscular dystrophy (DMD). Her brother (II-2) has a deletion in the DMD gene. Although her mother (1-2) does not have the deletion, individual II-1 is told that her risk for carrying the DMD gene is greater than that of the general population. Which of the following best explains this increased risk? Select one: a. Suspected parental consanguinity b. Promoter mutation c. Locus heterogeneity for DMD d. X inactivation e. Maternal germline mosaicism f. De novo gene mutation
d. Sister 2 is a carrier
A 3-year-old boy is suspected of having an X-linked immunodeficiency. To establish the pattern of transmission of this genetic defect, DNA is extracted from the T and B lymphocytes of his parents, his two sisters ages 5 and 7 years, and his 3-month-old brother. After restriction enzyme digestion, the digested DNA is subjected to gel electrophoresis and probed with a DNA marker that distinguishes the maternal and paternal X chromosome alleles. The results are shown. Based on this DNA analysis, which of the following statements is correct concerning the inheritance of this genetic deficiency? Select one: a. Both sisters are carriers b. Neither sister is a carrier c. Both parents can transmit the defective gene d. Sister 2 is a carrier e. Sister 1 is a carrier f. The brother has inherited the defective gene
d. succinyl-CoA
A 3-year-old child presents with a history of recurrent rash upon sun exposure and passage of purple-colored urine. The child is diagnosed with congenital erythropoietic porphyria (CEP), a disorder associated with the pathway of heme biosynthesis. Which of the following intermediates of TCA cycle is used as a precursor for heme biosynthesis? Select one: a. succinate b. pyruvate c. malate d. succinyl-CoA e. acetyl-CoA
d. Expansion of trinucleotide repeat
A 35-year-old woman, gravida 2, para 2, comes to the physician for preconceptional counseling. She has an 8-year-old daughter and a 5-year-old son. Both have mild developmental delay. The woman's brother, aged 32 has mild mental retardation and fragile X syndrome. Which of the following is the most likely cause of the developmental delay in this woman's children? Select one: a. Chromosomal aneuploidy b. Uniparental disomy c. Imprinting d. Expansion of trinucleotide repeat e. X chromosome deletion
d. Regulation of apoptosis
A 48-year-old man has a painless enlarged axillary lymph node. Excisional biopsy shows replacement of nodal architecture by neoplastic follicles composed of small cleaved lymphocytes. Cytogenetic studies show a t (14;18). Alteration of which of the following processes most consistently underlies the pathogenesis of this lesion? Select one: a. Growth factor production b. Nuclear transcription factor expression c. Growth factor receptor regulation d. Regulation of apoptosis e. DNA repair
e. aconitase
A 5-year-old child was rushed to emergency room after accidentally consuming fluoroacetate, a known inhibitor of TCA cycle. Which of the following enzymes is inhibited by fluoroacetate? Select one: a.malate dehydrogenase b. succinate dehydrogen c. citrate synthase d. isocitrate dehydrogenase e. aconitase
d. stimulation of cyclic GMP formation
A 50-year-old man with anginal pain takes nitroglycerin. The pain is rapidly relieved because of Select one: a. stimulation of inositol 1,4,5-trisphosphate formation b. stimulation of cyclic AMP formation c. inhibition of phospholipase C activity d. stimulation of cyclic GMP formation e. stimulation of protein kinase C activity
a. mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS)
A 6-year-old boy is brought to his pediatrician because his parents are concerned about the appearance of seizures and stroke-like episodes. Upon examination the parents reveal that their son has recently begun to exhibit a progressive incoordination in his walking and also difficulty picking up his toys. The physician notes that the patient is short for his age and an eye examination reveals pigmentary retinopathy. Analysis of blood shows elevated levels of lactic acid. These signs and symptoms are most indicative of which of the following disorders? Select one: a. mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) b. Leigh syndrome c. Kearns-Sayre syndrome (KSS) d. erythrocyte pyruvate kinase deficiency e. Type 2 diabetes
e. Homologous sites
A geneticist has artificially produced a microorganism that contains a new combination of genes. He wants to know if recombination or transposition has occurred. The major difference between these two processes is that recombination involves which of the following? Select one: a. Endonuclease sites b. Sites on the same chromosome c. Gene rearrangement d. DNA repair e. Homologous sites
c. NADH dehydrogenase
A laboratory analysis of isolated mitochondria demonstrates that oxygen consumption is normal when succinate is added but extremely low when pyruvate and malate are used. The mitchondria are subsequently shown to have normal cytochromes but a reduced iron content. The reduced pyruvate/malate oxidation is due to a defect in which of the following respiratory components? Select one: a. ubiquinone b. succinate dehydrogenase c. NADH dehydrogenase d. cytochrome oxidase e. cytochrome c
e. enhanced rate of transcription
A mutation that resulted in the loss of histone deacetylation activity in a eukaryotic cell line would be expected to have what effect on transcription? Select one: a. reduced rate of transcription b. conversion of repressors into activators c. conversion of activators into repressors d. no effect e. enhanced rate of transcription
b. increases the apparent Km for glucose 1-phosphate
A newborn screening test for galactosemia is positive in your patient. Genetic studies demonstrate the infant harbors a particular mutation in the GALT gene that impairs the activity of galactose-1-phosphate uridyltransferase. The impaired enzyme cannot convert galactose 1-phosphate and UDP-glucose to UDP-galactose and glucose 1-phosphate. Galactose 1-phosphate accumulates and affects the activity of UTP-dependent glucose-1-phosphate pyrophosphorylase (UGP). Which of the following actions by galactose 1- phosphate proves that it is a competitive inhibitor of UGP? Select one: a. increases the Vmax for glucose 1-phosphate b. increases the apparent Km for glucose 1-phosphate c. decreases both the Vmax and the apparent Km for glucose 1-phosphate d. decreases the Vmax for glucose 1-phosphate e. decreases the apparent Km for glucose 1-phosphate
b. electron transport ejects H+ into the intermembrane space
According to the chemiosmotic theory of how oxidation and phosphorylation are coupled, which of the following processes produces the chemical gradient that drives the generation of ATP from ADP? Select one: a. electron transport causes H+ to penetrate the inner mitochondrial membrane b. electron transport ejects H+ into the intermembrane space c. NADH is regenerated from NAD+ d. osmotic forces cause H+ to bind with FAD in the mitochondrial matrix e. FADH2 is regenerated from FAD
a. aspartate, glycine, and glutamine
Amino acids that contribute at least one nitrogen or carbon to the purine ring during the biosynthesis of purine nucleotides are Select one: a. aspartate, glycine, and glutamine b. aspartate, arginine, and histidine c. alanine, asparagine, and lysine d. glycine, serine, and tyrosine e. alanine, methionine, and histidine
e. pyruvate carboxylase
Anaplerotic reactions are those that result in replenishing intermediates in the TCA cycle. Which of the following enzymes catalyzes an anaplerotic reaction? Select one: a. citrate synthase b. malate dehydrogenase c. succinyl-CoA synthetase d. pyruvate kinase e. pyruvate carboxylase
d. histone acetylation tends to destabilize chromatin structure
Chromatin remodeling is associated with alterations in the transcriptional activity of genes in the region of the remodeling. Which of the following statements is most correct concerning the events of chromatin remodeling? Select one: a. methylation of histone H1 is sufficient to stimulate remodeling b. chromatin remodeling occurs predominantly in regions enriched in CpG dinucleotides c. remodeling is necessary to induce the property of genomic imprinting d. histone acetylation tends to destabilize chromatin structure e. methylation of guanine residues induces the remodeling event
c. it is induced in the G1-phase nucleus
Control of specific steps in the cell cycle can be studied in cell culture by the use of cell fusion experiments. If cells that are currently in S-phase of the cell cycle are fused with cells that are in the G1-phase of the cell cycle, which of the following would most correctly reflect the process of DNA synthesis? Select one: a. it is stimulated in the S-phase nucleus b. it is unaffected in the G1-phase nucleus c. it is induced in the G1-phase nucleus d. it is inhibited in the S-phase nucleus
a. increase Km but no change in Vmax
Drugs that inhibit enzymes in a competitive manner will have which of the following effects on the Michaelis-Menten equation derived parameters: Vmax and/or Km? Select one: a. increase Km but no change in Vmax b. increase Vmax but no increase in Km c. decrease Km but no effect on Vmax d. decrease Vmax but no change on Km e. decrease both Vmax and Km
e. decrease Vmax but no change on Km
Drugs that inhibit enzymes in a noncompetitive manner will have which of the following effects on the Michaelis-Menten equation derived parameters: Vmax and/or Km? Select one: a. decrease Km but no effect on Vmax b. increase Vmax but no increase in Km c. increase Km but no change in Vmax d. decrease both Vmax and Km e. decrease Vmax but no change on Km
d. decrease both Vmax and Km
Drugs that inhibit enzymes in an uncompetitive manner will have which of the following effects on the Michaelis-Menten equation-derived parameters: Vmax and/or Km? Select one: a. decrease Km but no effect on Vmax b. increase Vmax but no increase in Km c. decrease Vmax but no change on Km d. decrease both Vmax and Km e. increase Km but no change in Vmax
b. −5.4 kJ/mol
During glycolysis, glucose 1-phosphate is converted to fructose 6-phosphate in 2 successive reactions: For the overall reaction which of the following correctly identifies the freeenergy change? Select one: a. +5.4 kJ/mol b. −5.4 kJ/mol c. +8.8 kJ/mol d. −8.8 kJ/mol e. −7.1 kJ/mol
a. ultraviolet light
Environmental factors can result in the incorporation of mutations into DNA. Many mutagenic compounds and various forms of radiation lead to mutations through the activity of an error-prone DNA repair mechanism. Which of the following causes mutations by the process of dimerization of adjacent pyrimidines? Select one: a. ultraviolet light b. nitrous acid c. γ-radiation d. 5-bromouracil e. hydroxylamine
b. shape and size of the subunit
Eukaryotic ribosomes consist of 2 subunits designated as 40S and 60S. The S value is most dependent on which of the following properties of the subunit? Select one: a. RNA content b. shape and size of the subunit c. composition of the RNA bases d. interactions between the RNA and protein components e. protein content
d. Y
From the values of AG˚ given in the table, which compound in the overall metabolic pathway V <->W <-> X <-> Y <-> Z will accumulate in the largest amount at equilibrium? Select one: a. W b. X c. V d. Y e. Z
c. telomere
Functional eukaryotic chromosomes contain stretches of DNA harboring specialized nucleotide sequences. Which of the following represents the type of DNA sequence that prevents the strands from becoming shorter with each replication cycle? Select one: a. intron b. centromere c. telomere d. kinetochore e. replication origin
a. phenotype differences are independent of genotype variation
Genomic imprinting is termed "epigenesist," which is defined by which of the following? Select one: a. phenotype differences are independent of genotype variation b. gene expression results from regulated levels of DNA methylation c. genotype differences are not reflected by phenotype differences d. gene expression that is restricted to a specific cell lineage e. gene regulation is exerted by sex-type specific factors
b. −7.8 kcal/mol
Given the table of values for the hydrolysis of some phosphorylated compounds, which of the following best describes the ΔG0′ for the following reaction? Select one: a. −7.0 kcal/mol b. −7.8 kcal/mol c. −22.1 kcal/mol d. −14.8 kcal/mol e. −5.0 kcal/mol
c. ΔG0′ = −11 kJ/mol
Hydrolysis of 1 M glucose 6-phosphate catalyzed by glucose 6-phosphatase is 99% complete at equilibrium (ie, only 1% of the substrate remains). Which of the following statements is most nearly correct? (R = 8.315 J/mol·K; T = 298 K) Select one: a. ΔG0′ = +11 kJ/mol b. ΔG0′ = −5 kJ/mol c. ΔG0′ = −11 kJ/mol d. ΔG0′ = 0 kJ/mol e. ΔG0′ cannot be determined from the information given
a. 115/200
In a clinical study, 100 subjects are examined for a particular genetic alteration hypothesized to be related to prostate cancer. The results are shown in the table. If A is one allele, and B is the other, which of the following is the frequency of the B allele? Select one: a. 115/200 b. 45/200 c. 25/200 d. 90/200 e. 50/200
e. Asp
In an enzyme with a critical glutamic acid residue (Glu, E) in the active site, which of the following amino acid substitutions would be expected to have the least effect on enzyme activity? Select one: a. Arg b. Lys c. Tyr d. Ser e. Asp
c. 30
In analyzing a sample of double-stranded DNA, it has been determined that the molar amount of adenosine is 20%. Given this information, what is the content of cytidine? Select one: a. 40 b. 20 c. 30 d. 10 e. 60
b. stimulation of pyruvate dehydrogenase activity by Ca2+
In exercising skeletal muscles, pyruvate oxidation in the TCA cycle is stimulated by which of the following? Select one: a. allosteric activation of malate dehydrogenase by NAD+ b. stimulation of pyruvate dehydrogenase activity by Ca2+ c. allosteric activation of isocitrate dehydrogenase by NADH d. phosphorylation of α-ketoglutarate dehydrogenase to an inactive form e. increased product inhibition of citrate synthase by oxaloacetate
c. Phosphoribosylpyrophosphate synthetase
In gout, hyperuricemia resulting from overproduction of urate is most likely to result from a lack of feedback inhibition by ADP or GDP at which enzyme? Select one: a. Glucose 6-phosphate dehydrogenase b. Nucleotide phosphorylase c. Phosphoribosylpyrophosphate synthetase d. Dihydrofolate reductase e. Adenosine deaminase
e. succinate-CoA synthetase
In the TCA cycle, GTP is produced via a process referred to as substrate-level phosphorylation. Which of the following enzymes is involved in this process of formation of GTP from GDP? Select one: a.malate dehydrogenase b. citrate synthase c. succinate dehydrogenase d. isocitrate dehydrogenase e. succinate-CoA synthetase
b. transferases
Kinases are a class of enzymes that incorporate a phosphate onto their substrates. The catalytic activity of kinases classifies them as members of which of the following enzyme families? Select one: a. oxidoreductases b. transferases c. isomerases d. ligases e. hydrolases
d. glycine
Mutational studies on collagen proteins demonstrate that substitution of one particular amino acid significantly affects the normal structure of the collagen molecules. Which of the following amino acids is absolutely required for the stable formation of the collagen triple helix? Select one: a. tryptophan b. alanine c. cysteine d. glycine e. phenylalanine
e. lactate
Pyruvate dehydrogenase complex (PDHc) deficiency is an autosomal recessive disorder and leads to anion gap metabolic acidosis. Which of the following accumulates to cause metabolic acidosis? Select one: a. acetoacetate b. β-hydroxy butyrate c. fumarate d. hydrochloric acid e. lactate
b. NAD+
Regeneration of which of the following participants in the TCA cycle is dependent on the presence of oxygen? Select one: a. ADP b. NAD+ c. citrate d. succinate e. α-ketoglutarate
d. 5′ → 3′ synthesis of DNA from an RNA template
Reverse transcriptase is a specialized form of polymerase. Which of the following most correctly describes the function of this special polymerase? Select one: a. 3′ → 5′ synthesis of RNA from a DNA template b. 5′ → 3′ synthesis of RNA from a DNA template c. 3′ → 5′ synthesis of DNA from an RNA template d. 5′ → 3′ synthesis of DNA from an RNA template
e. Restriction fragment length polymorphism
Southern blotting is used to distinguish maternal and paternal copies of chromosome 7 in a single person. The diagram on the top indicates the DNA region that is amplified and the predicted sites of digestion with restriction endonucleases. The site of hybridization of the labeled probe is also indicated. The gel pattern obtained is shown on the bottom. This pattern is most likely indicative of which of the following? Select one: a. Meiotic segregation b. Chromosome walking c. Recombination d. Nondisjunction of chromosomes during meiosis e. Restriction fragment length polymorphism
b. 1 in 3600
Tay-Sachs disease is an autosomal recessive disorder for which the carrier frequency in individuals of Ashkenazi Jewish descent is about 1 in 30. On the basis of this carrier frequency, which of the following is the best estimate of the probability that a child born to two parents, both of whom are of Ashkenazi Jewish descent, will be affected by Tay-Sachs disease? Select one: a. 1 in 60 b. 1 in 3600 c. 1 in 15 d. 1 in 900 e. 1 in 450 f. 1 in 1800
d. RNA-dependent DNA polymerase
Telomerase is the specialized activity that allows for replication of the telomeric ends of the chromosomes. In addition to an RNA that is complimentary to the telomeric repeat sequence what other component is required of this complex for its normal activity? Select one: a. RNA-dependent RNA polymerase b. DNA helicase c. DNA-dependent DNA polymerase d. RNA-dependent DNA polymerase e. DNA-dependent RNA polymerase
b. unwind the DNA duplex during replication
The anticancer drug etoposide functions because it inhibits the activity of topoisomerase. Which of the following represents the normal function of this enzyme? Select one: a. remove mismatched nucleotides at the end of replication b. unwind the DNA duplex during replication c. remove the RNA primer from each Okasaki fragment d. stabilize single-stranded regions of DNA at the replication fork e. introduce the primer onto the template of DNA prior to replication
d. Gly → Leu
The parents of a 3-year-old boy bring him to the hospital following a fall as they are concerned he has broken his arm. His parents report that over the past year he has had several episodes of what they think is uncharacteristically easy fractures in his legs from minor falls. They indicate that there is no family history of bone disease. Physical examination shows bowing and deformities of the legs, and x-rays show evidence of previous fractures and osteopenia. The physician suspects a collagen defect and orders a skin biopsy. The results of the biopsy show unstable type I collagen that is due to a single-point mutation in one of the type I genes. This mutation is most likely caused by which of the following amino acid substitutions in this patient? Select one: a. Tyr → Trp b. Ala → Asp c. Ser → Phe d. Gly → Leu e. Glu → Gln
b. C-N-C-C
The peptide bond of all proteins forms with highly specific orientation. This orientation contains atoms linked in which of the following ways? Select one: a. C-O-N-C b. C-N-C-C c. C-S-S-C d. C-N-H-C e. C-C-O-N
a. dephosphorylation
The pyruvate dehydrogenase complex (PDHc) is a multi-subunit enzyme whose activity is regulated by both allosteric effectors and covalent modification. Which of the following exerts a positive influence on the activity of PDHc toward pyruvate? Select one: a. dephosphorylation b. acetyl-CoA c. NADH d. phosphorylation e. ATP
b. ΔG0′
Which of the following indicates whether the reaction, A → B, is thermodynamically favorable under standard state conditions at near physiological pH? Select one: a. ΔG′ b. ΔG0′ c. Vmax d. Keq e. Km
c. 3′ to 5′ exonuclease activity
You are carrying out experiments to study DNA replication in a cell line derived from a breast cancer tumor. You discover that the DNA polymerase in these cells incorporates the incorrect nucleotide into the elongating strand approximately once every thousand bases. These errors suggest that the "proofreading" capacity of the polymerase is defective. This would be indicative of the following processes not being correctly carried out by the defective polymerase? Select one: a. topoisomerase-mediated cleavage of the DNA backbone b. insertion of nucleotides in 5′ to 3′ orientation c. 3′ to 5′ exonuclease activity d. 5′ to 3′ exonuclease activity e. synthesis of ribonucleotide polymers
c. aspartate
You are examining the lipid-interaction characteristics of a particularly hydrophobic protein. Mutational studies with this protein have been designed to examine these lipid interaction properties. Addition of which of the following amino acids to the protein would most likely be expected to interfere with the lipid-interaction properties? Select one: a. isoleucine b. glycine c. aspartate d. leucine e. valine
b. deoxyadenosine
You are treating a 4-year-old child who has been afflicted with recurrent infections. The child exhibits retarded development, weakness, and weight loss. Physical examination also shows absent tonsils and blood work reveals a lack of lymphocytes. These signs and symptoms are typical of severe combined immunodeficiency syndrome. Which of the following compounds would be expected to be elevated in the blood of this patient? Select one: a. xanthine b. deoxyadenosine c. bilirubin d. cytosine e. deoxythymidine
d. cystic fibrosis
A 12-year-old boy has suffered from chronic sinopulmonary disease including persistent infection of the airway with Pseudomonas aeruginosa. He has constant and chronic sputum production because of the airway infection. Additionally, he suffers from gastrointestinal (GI) and nutritional abnormalities that include biliary cirrhosis, meconium ileus, and pancreatic insufficiency. The symptoms are classical for which of the following disorders? Select one: a. Tay-Sachs disease b. sickle cell anemia c. renal Fanconi syndrome d. cystic fibrosis e. congenital adrenal hyperplasia
f. Methylation of E. Coli DNA
DNA from Escherichia coli and Haemophilus influenzae is digested with the restriction endonuclease EcoRI and the fragments separated by agarose gel electrophoresis. An examination of the gel shows that the DNA from H. influenzae was cleaved into numerous smaller fragments while that from E. Coli was not. Which of the following best explains this difference? Select one: a. Presence of introns in H. Influenzae DNA b. Presence of transposons in E. Coli DNA c. Presence of introns in E. Coli DNA d. Presence of transposons in H. Influenzae DNA e. Methylation of H. Influenzae DNA f. Methylation of E. Coli DNA
d. topoisomerase I
The camptothecins are an alkaloid class of anticancer drugs used in the treatment of colon and breast cancers. These compounds function by inhibiting the activity of which of the following enzymes? Select one: a. DNA polymerase b. DNA ligase c. histone deacetylase d. topoisomerase I e. ATP-dependent DNA helicase
e. DNA
This motif of a steroid homone receptor binds specifically to which of the following compounds? Select one: a. ATP b. Cyclic AMP c. RNA d. Steroid hormone e. DNA
d. changing the conformation of the enzyme
Which of the following is the mechanism by which allosteric effectors influence enzymatic activity? Select one: a. increasing hydration of the active site b. forming high-energy complexes with substrate c. protecting against degradation of the enzyme d. changing the conformation of the enzyme e. binding at the catalytic site
d. disruption of pH gradient across mitochondrial membrane
Which of the following is the most likely mechanism of action of a pharmacological agent that prevents ATP generation in isolated mitochondria? Select one: a. decrease of NADH generation by NADH dehydrogenase b. increase of transport of pyruvate through the mitochondrial membrane c. inhibition of glyceraldehydes-3-phosphate dehydrogenase d. disruption of pH gradient across mitochondrial membrane e. activation of cytochrome c
e. Nuclear transcription factors
Which of the following most affects expression of specific cellular RNAs in the fast-growing liver cells of an infant? Select one: a. Mitochondrial proteins b. Ribosomes c. Vitamins d. Peroxisomal proteins e. Nuclear transcription factors
d. correct folding of nascent proteins
You are studying the relationships between protein structure and function. You are most interested in the characteristics of a family of proteins termed chaperones. Which of the following processes requires chaperone activity in order to facilitate correct biological function? Select one: a. assembly of coated pits b. interaction between actin and myosin c. formation of tight junctions d. correct folding of nascent proteins e. processing of telomeres
c. Transmembrane diffusion and binding of signaling molecule to transcription factor
A 54-year-old man with alcoholism is brought to the emergency department because of a 10-day history of weakness, confusion, and shortness of breath. He drinks approximately three fourths of a liter of liquor daily. He appears wasted, and there is an odor of alcohol on his breath. His respirations are 32/min. Physical examination shows jaundice, abdominal distention, spider angiomata, and Tanner stage 2 gynecomastia. Laboratory studies show hypoalbuminemia and an increased serum estrogen-to-androgen ratio. The development of gynecomastia in this patient is mediated primarily by which of the following signal transduction pathways? Select one: a. Activation of phospholipase C and generation of inositol 1,4,5-trisphosphate b. G protein-coupled activation of adenylyl cyclase c. Transmembrane diffusion and binding of signaling molecule to transcription factor d. Receptor dimerization and autophosphorylation of tyrosine residues e. Activation of phospholipase A, and generation of arachidonic acid
b. Inhibiting thymidylate synthetase activity
A 56-year-old man who has colon cancer is being treated with 5-fluorouracil. Which of the following is the mechanism of the antineoplastic action of this drug? Select one: a. Inhibiting ribonucleotide reductase activity b. Inhibiting thymidylate synthetase activity c. Inhibiting carbamoyl phosphate synthetase I d. Binding free dihydrofolate
b. troponin I
A 57-year-old man has just returned from an overseas trip and reports having had severe substernal chest pain 3 days ago. Which of the following is the most appropriate laboratory test to order for this patient? Select one: a. lactate dehydrogenase, LD1 fraction b. troponin I c. aspartate aminotransferase d. creatine kinase, MB fraction e. creatine kinase, total
d. Free rotation of the two sections of the DNA helix on either side of the nick
During DNA replication in eukaryotic cells, which of the following occurs when topoisomerase I cleaves a phosphodiester bond in one DNA strand? Select one: a. Removal and subsequent transfer of a small piece of DNA to another position on the chromosome b. Removal of mismatched nucleotides that could result in deleterious mutations c. A recombination event between adjacent double helices d. Free rotation of the two sections of the DNA helix on either side of the nick
c. Multifactorial
The developmental anomaly shown in this stillborn fetus is most commonly characterized by which type of inheritance? Select one: a. Sex-linked b. Mitochondrial c. Multifactorial d. Autosomal recessive e. Autosomal dominant
d. decreases Vmax
The drug acetazolamide is used in the treatment of glaucoma since it decreases the production of aqueous fluid, thereby reducing intraocular pressures. This drug is a noncompetitive inhibitor of carbonic anhydrase. Which of the following statements most accurately relates to the actions of this type of inhibitor? Select one: a. decreases apparent Km b. increases apparent Km c. increases Vmax d. decreases Vmax e. decreases both Vmax and apparent Km
a. oxaloacetate is removed by citrate synthase
The equilibrium constant for the reaction catalyzed by malate dehydrogenase (malate + NAD+ ↔ oxaloacetate + NADH + H+) is 10−4. However, in vivo, the production of oxaloacetate is favored because of which of the following? Select one: a. oxaloacetate is removed by citrate synthase b. the buildup of malate results in the formation of succinate c. oxaloacetate cannot cross the mitochondrial membrane and is trapped in the matrix d. malate leaves the mitochondrial matrix by a symport carrier along with phosphate
e. histidine
The greatest buffering capacity at physiological pH would be provided by a protein rich in which of the following amino acids? Select one: a. alanine b. cysteine c. proline d. tyrosine e. histidine
d. B
The kinetics of an allosteric enzyme is shown in the graph. An experimental drug (Drug X) is added, and the results are shown. Which of the following sets of findings best describes the effect of Drug X on enzyme activity? Select one: a. F b. G c. D d. B e. I f. H g. E h. C i. A
a. Protein truncation
The nucleotide sequence encoding four amino acids near the amino terminus of a 10- kd protein is 5'- ACT GAT TGC GTT -3'. This sequence is mutated by insertion of a single nucleotide (A) in the second codon and becomes 5'- ACT GAA TTG CGT -3'. Which of the following consequences of this mutation is most likely? Select one: a. Protein truncation b. Single amino acid substitution c. Decreased rate of transcription d. Altered cell-cycle checkpoint
b. apo-B48
The process of RNA editing leads to sequence changes that are not reflective of the genetic information contained within the gene for an edited RNA. RNA editing occurs through the action of specific nucleotide deaminases that change either adenine to inosine or cytidine to uridine. These nucleotide changes can affect the coding or splicing capacity of the RNA. Which of the following proteins is an important example of the result of RNA editing? Select one: a. glutamate dehydrogenase b. apo-B48 c. tissue factor (factor III) d. calcitonin gene related peptide (CGRP) e. ferritin
d. structure resulting from the interactions between multiple polypeptide chains
The quaternary structure of a given protein is defined by which of the following? Select one: a. organization of super-secondary structures within the protein b. linear order of the amino acids c. overall structure resulting from association of domains within the protein d. structure resulting from the interactions between multiple polypeptide chains e. ordered organization of secondary structures within the protein
e. fumarate would become reduced, FADH2 would become oxidized
The standard reduction potentials (E0') for the following half reactions are given. If you mixed succinate, fumarate, FAD, and FADH2 together, all at 1-M concentrations and in the presence of succinate dehydrogenase, which of the following would happen initially? Select one: a. no reaction would occur because all reactants and products are already at their standard concentrations b. fumarate and succinate would become oxidized; FAD and FADH2 would become reduced c. succinate would become oxidized, FADH2 would be unchanged because it is a cofactor d. succinate would become oxidized, FAD would become reduced e. fumarate would become reduced, FADH2 would become oxidized
a. 2 moles of CO2 are released during each circuit of the cycle
There is no net synthesis of 4-carbon precursors of glucose during the metabolic breakdown of acetyl-CoA in the TCA cycle because of which of the following reason? Select one: a. 2 moles of CO2 are released during each circuit of the cycle b. oxidative decarboxylation reactions prevent oxaloacetate production by producing allosteric inhibitors c. insufficient NADH for gluconeogenesis is produced in the mitochondrial matrix during oxidation-reduction reactions of the cycle d. the mitochondrial membrane is impermeable to oxaloacetate which is trapped in the matrix
a. ΔG0′ is −4.44 kJ/mol
When a mixture of 3-phosphoglycerate and 2-phosphoglycerate is incubated at 25°C with phosphoglycerate mutase until equilibrium is reached, the final mixture contains 6 times as much 2-phosphoglycerate as 3-phosphoglycerate. Which one of the following statements is most nearly correct, when applied to the reaction as written? (R = 8.315 J/mol·K; T = 298 K) 3-Phosphoglycerate → 2-phosphoglycerate Select one: a. ΔG0′ is −4.44 kJ/mol b. ΔG0′ is +12.7 kJ/mol c. ΔG0′ is zero d. ΔG0′ is incalculably large and positive e. ΔG0′ cannot be calculated from the information given
e. p53
When dividing cells are progressing through the cell cycle, many checks are imposed to ensure that the process is occuring with fidelity. A critical checkpoint in the cell cycle occurs in response to DNA damage, such as that induced by UV light. Which of the following cell-cycle proteins is involved in DNA damage-mediated cell-cycle arrest? Select one: a. E2F b. cyclin D c. cyclin A d. CDK2 e. p53
a. cAMP
When glucagon binds to its receptors on the surface of adipose tissue, it activates a signaling cascade leading to the release of free fatty acids that can be utilized by the liver and other peripheral tissues for energy production. Which of the following is the correct nucleic acid involved in the triggering of this cascade? Select one: a. cAMP b. cGMP c. GTP d. ATP e. xanthine
a. acetyl-CoA
Which of the following CoA derivatives serves the dual function of channeling carbon units into the TCA cycle for oxidative catabolism and acting as a precursor for lipid biosynthesis? Select one: a. acetyl-CoA b. acetoacetyl-CoA c. propionyl-CoA d. malonyl-CoA e. HMG-CoA
d. transport down the axon from the neuronal cell body along the microtubules
Which of the following best describes how mitochondria reach the presynaptic endings of nerve cells? Select one: a. ameboid migration down the axon from the neuronal cell body b. assembly within the presynaptic ending from cytoplasmic lipids, amino acids, and other small molecules c. diffusion down the axon from the neuronal cell body d. transport down the axon from the neuronal cell body along the microtubules e. assembly within the presynaptic ending using recycled presynaptic membranes
d. their inhibitory activity is unaffected by substrate concentration
Which of the following best explains why noncompetitive inhibitors of enzymes generally make better pharmaceuticals? Select one: a. they bind to the same site as the substrate b. they affect only Km and not Vmax c. they increase the rate of degradation of the target enzyme d. their inhibitory activity is unaffected by substrate concentration e. they irreversibly inhibit the enzyme
e. anthracyclins
Which of the following class of compounds is known to inhibit topisomerse II and thus have shown utility as cancer chemotherapeutics? Select one: a.antimetabolites b. taxanes c. vinca alkaloids d. camptothecins e. anthracyclins
a. coenzyme Q and flavins
Which of the following components of mitochondrial electron transport can act as 1-electron or 2-electron carriers? Select one: a. coenzyme Q and flavins b. NADH, non-heme iron, cytochrome c, coenzyme Q, and flavins c. cytochrome c, coenzyme Q, and flavins d. non-heme iron, cytochrome c, coenzyme Q, and flavins
c. ATP synthase
Which of the following components of the electron transport system is inhibited by oligomycin? Select one: a. complex I b. complex IV c. ATP synthase d. complex III e. complex II
c. pH at which a molecule is electrically neutral
Which of the following correctly defines the isoelectric point (pI) of an amino acid or protein? Select one: a. the ion constant of water b. negative log of the concentration of H+ c. pH at which a molecule is electrically neutral d. pH at which an equivalent distribution of acid and conjugate base exists in solution e. the equilibrium constant for the ionization of the substance
b. pH at which an equivalent distribution of acid and conjugate base exist in solution
Which of the following correctly defines the term pKa? Select one: a. ion constant of water b. pH at which an equivalent distribution of acid and conjugate base exist in solution c. pH at which a molecule is neutrally charged d. equilibrium constant for the dissociation of HA to A− and H+ e. negative log of the concentration of H+
a. they possess binding sites for regulatory molecules in addition to substratebinding sites
Which of the following relates to allosteric enzymes? Select one: a. they possess binding sites for regulatory molecules in addition to substratebinding sites b. they require additional cofactor-binding sites for subsequent binding of substrate c. they can bind more than one substrate simultaneously d. they can convert multiple different substrates to product e. they are inactive on their substrates in the absence of accessory proteins
a. it is a methylated guanine
Which of the following represents a characteristic feature of the cap structure on the 5′ end of most eukaryotic mRNAs? Select one: a. it is a methylated guanine b. it is a guanine found attached to a cytidine dinucleotide in the context G-C-C c. it is a methylated adenine d. it is a methylated cytidine e. it is an adenine found attached to a cytidine dinucleotide in the context A-C-C
b. two copies each of histone H2A, H2B, H3, and H4
Which of the following represents the correct composition of a eukaryotic nucleosome core? Select one: a. one copy each of histone H2A, H3, and H4 b. two copies each of histone H2A, H2B, H3, and H4 c. one copy each of histone H1, H2A, and H2B d. histone H1 e. two copies each of histone H1, H2A, H3, and H4
b. its catalytic function is to synthesize ATP in a reaction driven by a chemiosmotic potential
Which of the following statements best characterizes ATP synthase? Select one: a. it couples ATP export from the mitochondrial matrix to ATP synthesis b. its catalytic function is to synthesize ATP in a reaction driven by a chemiosmotic potential c. the low H+ ion concentration outside mitochondria establishes an electrochemical gradient that drives ATP synthesis d. oligomycin binds to ATP synthase, directly preventing ATP export e. it is soluble protein found in the mitochondrial matrix
c. a unique RNA molecule serves as the template for synthesis
Which of the following statements reflects the process by which of the telomeric ends of chromosomes are replicated? Select one: a. telomeres are replicated as short tandem repeated stretches of ribonucleotides instead of deoxyribonucleotides b. short template-independent blocks of DNA are ligated to the ends using a 5′→ 5′ bond c. a unique RNA molecule serves as the template for synthesis d. a unique DNA molecule serves as the primer for synthesis e. telomeres are replicated in a temple-independent process
d. deamination of m5C produces T
Within human chromosomes there are regions of highly concentrated GC content. Many of the cytosine residues that fall within CpG dinucleotide sequences are methylated at the 5 position (m5CpG). Which of the following best explains why these methyl-CpG sequences are exceptionally prone to mutation? Select one: a. methylation of C directly changes its base-pairing properties b. homologous recombination occurs preferentially at m5C sequences c. methylation of C directly interfere with base-pairing during DNA replication d. deamination of m5C produces T e. histones bind less tightly to m5C sequences than to other sequences
d. topoisomerase
You are carrying out experiments to study DNA replication in a cell line derived from a breast cancer tumor. You discover that the replication process does not completely copy all of each chromosome. Examination of the process using electron microscopy indicates that replication ceases near to where the DNA strands are attached to the chromatin scaffold. Given these observations, which of the following activities is most likely to be defective in these cells? Select one: a. DNA ligase b. helicase c. single-stranded binding proteins d. topoisomerase e. polymerase-α
b. loss of intron splicing
You are examining the process of RNA synthesis in a cell line derived from a pancreatic tumor. You discover that the cells do not contain any U1 small nuclear RNA (snRNA). The lack of this RNA species in these cells is most likely to have which of the following effects on overall RNA synthesis? Select one: a. synthesis of only rRNAs b. loss of intron splicing c. failure of capping mRNAs d. no synthesis of any mRNAs e. defective polyA tail addition
a. secondary structure
You are examining the thermodynamically stable structures of proteins. In particular you are studying the α-helix and β-sheet conformations that form in the study proteins. These conformations correspond to which of the following? Select one: a. secondary structure b. primary structure c. tertiary structure d. native conformation e. quaternary structure
d. RNA editing
You are studying lipoprotein processing in a strain of mutant mice. You find that these mice synthesize the same apolipoprotein composition contained in lipoproteins made in the liver and the intestines, whereas, in wild-type mice there are 2 different sized apolipoproteins in these same tissues. Examination of the mRNA processing in the mutant mice would most likely show a defect in which of the following processes? Select one: a. differential capping b. alternative polyadenylation c. posttranscriptional modification converting a U to a T residue d. RNA editing e. alternative splicing
d. inhibition of hormone secretion
You are studying the activity of isolated anterior pituitary cells in culture. Specifically you are interested in the function of microtubules in these cells. Your studies involve the actions of the drug colchicine, which is a known inhibitor of microtubules function. Addition of colchicine to the culture medium will most likely result in which of the following in these pituitary cells? Select one: a. stimulation of Ca2+ transport b. induction of pseudopodia c. stimulation of Na+-K+ transport d. inhibition of hormone secretion e. inhibition of adenylate cyclase
d. extensive hydrogen bonding of the amino acid side chains of the protein and the membrane phospholipid tails
You are studying the characteristics of membrane-associated proteins. You have isolated and characterized both wild-type and mutant forms of a particular protein. The mutant protein does not remain anchored in the plasma membrane. Which of the following properties results in membrane anchoring of the wild-type protein and is likely defective in the mutant version? Select one: a. formation of ionic bonds between the amino acid side chains and the phospholipid tails b. disulfide bond formation between the protein and its phosphatidylinositol anchor c. formation of β-pleated sheet structures to maximize protein interactions with the phospholipid head group d. extensive hydrogen bonding of the amino acid side chains of the protein and the membrane phospholipid tails e. extensive hydrophobic interactions between the amino acid side chains of the protein and the membrane phospholipid tails
b. Km unchanged, Vmax decreased
You are studying the effects of a new drug on the activity of your favorite enzyme. The results of your assays indicate that the drug acts as a noncompetitive inhibitor. Which of the following changes to the Km and Vmax allowed that determination to be made regarding the drugs actions? Select one: a. Km decreased, Vmax increased b. Km unchanged, Vmax decreased c. Km increased, Vmax decreased d. Km decreased, Vmax unchanged e. Km unchanged, Vmax unchanged
b. D
You are studying the effects of compounds that inhibit the activity of succinate dehydrogenase, SDH. You demonstrate that malonate is a competitive inhibitor of this enzyme. Which of the following sets of findings would most likely provide ideal conditions for maximum inhibition of SDH by malonate? Select one: a. B b. D c. C d. A
a. phosphorylation
You are studying the processes of RNA transcription in a cell-free system. You find that although the RNA polymerase II in your system initiates transcription as expected, it does not complete the process. Which of the following modifications to the enzyme is most likely not taking place, thereby, explaining the lack of complete transcription? Select one: a. phosphorylation b. methylation c. acetylation d. ubiquitination e. 5′ capping
b. complex I
You are the physician examining a 6-year-old boy who has been experiencing progressive muscle weakness. You perform assays on muscle biopsy tissue from this patient and find that mitochondrial oxidation of succinate is normal but that pyruvate oxidation is severely impaired. Mitochondrial extracts demonstrate that the activity of the pyruvate dehydrogenase complex (PDHc) is normal as is the activity of malate dehydrogenase. These results are consistent with the patient harboring a defect in which of the following mitochondrial components? Select one: a. complex II b. complex I c. ATP synthase d. complex IV e. complex III