Biochemistry and Molecular Biology Concepts, Exams of Biochemistry

Download Biochemistry and Molecular Biology Concepts and more Exams Biochemistry in PDF only on Docsity! Biochemistry Cumulative Final Practice Questions with Correct Answers Latest Update What is a syndrome? - Correct Answer a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation What is dysplasia? - Correct Answer the presence of cells of an abnormal type within a tissue, which may signify a stage preceding the development of cancer. A globular, multi-pass integral membrane protein in the cytoplasmic membrane is LEAST likely to have: A: An asparagine residue on a surface exposed to the cytoplasm. B: A high-mannose oligosaccharide on its extracellular surface. C: A glutamate side chain extending into the lipid bilayer. D: A leucine side chain in direct contact with the lipid bilayer. E: A transmembrane alpha helix with a thirty degree tilt. - Correct Answer A glutamate side chain extending into the lipid bilayer. A graduate student inadvertently consumes 1200 calories of a solution of glucose that is uniformly radioactively labeled with 14C (all six carbons are 14C). One hour later, which of the following molecules or moieties will contain the LEAST amount of 14C: A: Liver glycogen B: Muscle glycogen C: The fatty acid moiety of triacylglycerol in adipose tissue D: The glycerol moiety of triacylglycerol in adipose tissue E: Ketone bodies in the blood - Correct Answer Ketone bodies in the blood What is the rate limiting enzyme of fatty acid synthesis? - Correct Answer Acetyl CoA carboxylase Acetyl CoA --> malonyl CoA - Correct Answer Acetyl CoA carboxylase in fatty acid synthesis HMG CoA ---> acetoacetate - Correct Answer HMG-CoA lyase in ketogenesis A healthy adult eats a balanced meal after a 16-hour fast. One hour later, which of the following enzymes would be MORE active than it was just prior to eating? A: Acetyl CoA carboxylase B: Glucose 6-phosphatase C: Glycogen phosphorylase a D: HMG CoA lyase E: Hormone-sensitive lipase - Correct Answer Acetyl CoA carboxylase What does this describe: intrauterine growth restriction (IUGR), a small face and mouth, high forehead, rocker bottom feet, and clenched fists with overlapping fingers. - Correct Answer Trisomy 18- Edwards syndrome Trisomy 13 (Patau Syndrome) - Correct Answer severe cleft lip and/or palate, microphthlamia, severe mental retardation, microcephaly, holoprosencephaly, NTDs, polydactyly, rocker-bottom feet, Which stage of the cell cycle corresponds with the highest levels of histone synthesis? - Correct Answer S Which of the following statements about amino acid side chains is TRUE? A: Serine provides strong buffering capacity at pH 7.0. B: Alanine absorbs ultraviolet light C: Glutamic acid and aspartic acid differ significantly in their isoelectric point (pI). D: Proline often produces a bend in the protein chain. E: Only D-amino acids are incorporated into human proteins. - Correct Answer Proline often produces a bend in the protein chain. Which of the following is a drug used as an immune-suppressant to prevent graft rejection? - Correct Answer Mycophenolic acid Which of the following might be expected to result in jaundice with high levels of unconjugated (indirect) bilirubin? A: obstruction of the bile duct B: cystic fibrosis C: Crigler-Najjar syndrome D: pyruvate dehydrogenase deficiency E: lead poisoning - Correct Answer Crigler-Najjar syndrome Which of the following lipoproteins contains Apo B-100, ApoE and Apo C-II? - Correct Answer mature VLDL Which of the following tissues undergoes aerobic glycolysis in both the fed and fasting states? A: Liver B: Erythrocytes C: Adipose D: Brain E: Heart muscle - Correct Answer Brain Metformin (Glucophage) is used to treat type II diabetes. In addition to its effect on lowering blood glucose levels it also reduces hyperlipidemia. One explanation for this latter effect is: - Correct Answer Metformin activates AMPK (Amp-dependent protein kinase) which leads to inactivation of acetyl CoA carboxylase Acetyl CoA carboxylase - Correct Answer the rate-limiting step in fatty acid synthesis acteyl-CoA to Malonyl CoA In the lac operon, the catabolite activator protein (CAP): - Correct Answer binds the CAP site when there is no or low glucose In prokaryotic translation, what establishes the ribosomal reading frame? - Correct Answer interactions between 16S rRNA and the Shine-Dalgarno sequence In polypeptides the side chains provide the major characteristics of the solution behavior of the protein. The ȕamyloid 1-42 peptide that is thought to cause many forms of Alzheimers contains 1 Arg (pK 12.5), 3 Asp (pK 3.9), 3 Glu (pK 4.7), 3 His (pK 6), and 2 Lys (pK 10.5). To break up the amyloid aggregates found in brains, investigators expose the plaques to detergent and low pH. What is the net charge of the ȕamyloid peptide at pH 1.0? - Correct Answer +7 In male patients who are hemizygous for X-linked glucose 6-phosphate dehydrogenase deficiency, pathophysiological consequences are more apparent in red blood cells than in other cells such as the liver. Which one of the following provides the most reasonable explanation for this different response? - Correct Answer Liver cells, in contrast to RBC, have alternative mechanisms besides the pentose phosphate pathway for the production of NADPH. In ABC transporters, one of the conformational changes of the alternating access mechanism is driven by: - Correct Answer The hydrolysis of ATP in an extramembrane domain. ATP/ADP decreases - Correct Answer PMF decreases ADP increases, H+ flow increases, O2 consumptions increases Humans store energy in macromolecules for mobilization during periods of fasting. After two days of fasting, the majority of energy for the body is generated by which of the following processes? - Correct Answer lipolysis Glycosaminoglycans are: - Correct Answer Negatively charged and hydrated What step of collagen synthesis requires vitamin C? - Correct Answer Hydroxylation of proline and lysine. Dyslipidemia is characteristic of both type 1 and type 2 diabetics. This is due, in part, to: - Correct Answer Decreased production of lipoprotein lipase By which kind of receptor and intracellular signaling mechanism do you expect that cortisol modulate ACTH secretion? - Correct Answer nuclear receptor acting through gene expression regulation. Chromosomal microarray is considered first line genetic testing for individuals with one or more congenital birth defects. This test assesses for copy number variants called microdeletions and microduplications. Chromosomal microarray should detect all of the following diagnoses except: A: 47,XX,+21 B: 22q11.2 deletion (DiGeorge) syndrome C: Monosomy X (Turner syndrome) D: balanced 4;6 chromosome translocation E: 22q11.2 duplication syndrome - Correct Answer balanced 4;6 chromosome translocation An allele-specific oligonucleotide (ASO): - Correct Answer utilizes a small DNA oligonucleotide to detect single nucleotide changes in DNA What are accurate characteristics of the NAD+/NADH? - Correct Answer - The molecules are water soluble. Both NAD+ and NADH contain a nicotinamide ring. Both NAD+ and NADH contain phosphate groups. Both NAD+ and NADH are present in the cytoplasm and in the matrix of mitochondria. HMG-CoA lyase - Correct Answer breaks down HMG CoA into acetoacetate this acetoacetate can be broken down into 3 hydroxybutarate HMG-CoA reductase - Correct Answer rate limiting enzyme in cholesterol synthesis A signaling protein is activated by phosphorylation at an SAT amino acid sequence where either phosphorylation of serine or threonine results in an active protein. In certain tumors, however, an activating mutation is found in this region that renders the protein active in the absence of any phosphorylation events. Which of the following amino acid mutations is most likely to activate the protein? A: A to E B: S to A C: T to A D: A to T E: S to Y - Correct Answer A to E A previously healthy 27 year old female presents with delirium and rapid weight loss two weeks after a serious car accident. Blood pH was 7.3. Radiology indicates cerebral edema. Bloodwork reveals elevated serum ammonia. The patient MOST LIKELY has a mutation in the gene encoding: - Correct Answer Ornithine transcarbamoylase A patient presents in the clinic complaining of producing excessive urine volume. You diagnose her with diabetes insipidus. Which of following statements BEST describe the cause of the disease? - Correct Answer A decreased arginine-vasopressin secretion by the posterior pituitary. A patient has decreased basal metabolism and low levels of thyroid hormone. TRH administration to this patient causes no changes in thyroid hormone levels. However, TSH administration causes a dramatic increase in thyroid hormone levels. You suspect a pituitary problem, consequently you clone and sequence the TRH receptor of this patient finding no mutations to your surprise. Which of the following statements may BEST describe the cause of the problem in this patient? - Correct Answer The gene encoding TSH has a mutation which causes a premature STOP codon. A mutation that increases the production of histone deacetylase would be expected to: - Correct Answer decrease the transcription of many genes A hematologist is studying an African American family as one of the children was recently diagnosed with sickle cell disease. Genetic tests show the parents both have sickle cell trait. The parents are trying to have another child. What is the chance their next child will also be born with sickle cell trait? - Correct Answer 50% What leads to hyperuricemia? - Correct Answer A: Chronic excessive alcohol consumption B: Glycogen-storage disease type Ia (von Gierke disease) C: Gout D: Hereditary fructose intolerance Does Ornithine transcarbamoylase deficiency lead to hyperuricemia? - Correct Answer no What leads to anemia? - Correct Answer - Glucose 6-phosphate dehydrogenase deficiency Pyruvate kinase deficiency UMP synthase deficiency Vitamin B12 deficiency does multiple carboxylase deficiency lead to anemia? - Correct Answer no Ammonia is a product of - Correct Answer glutamate dehydrogenase glutamate dehydrogenase - Correct Answer liver enzyme which removes an ammonia group from glutamate forming alpha-ketoglutarate Chemical bonds made possible by the activity of prolyl hydroxylase most directly stabilize which of the following collagen structures? - Correct Answer The triple helix domain of procollagen Gene replacement therapy is available or in clinical trials for which of the following diseases? A: Sickle cell disease B: Spinal muscular atrophy (SMA) C: Retinal dystrophy D: All of the above - Correct Answer all of the above In skeletal and cardiac muscle and adipose tissue, the FIRST cellular action of insulin is to: - Correct Answer Recruit insulin-sensitive GLUT4 transporters to the plasma membrane. phosphoenolpyruvate carboxykinase - Correct Answer Oxaloacetate -> phosphoenolpyruvate Gluconeogenesis, irreversible enzyme In cytosol Requires GTP What processes contribute to the liver synthesizing fatty acids from glucose? - Correct Answer - Citrate synthase Citrate lyase Malic enzyme Pyruvate dehydrogenase citrate synthase - Correct Answer Oxaloacetate + Acetyl CoA --> Citrate Metformin is used to treat Type 2 diabetes because it: - Correct Answer Decreases gluconeogenesis and hyperlipidemia. Mutation of which of the following would incapacitate local control of the lac operon in bacteria? - Correct Answer the operator One method we discussed to cure sickle cell disease involves utilizing CRISPR/Cas9 gene editing in patient cells. What specifically is being edited in the method we discussed? - Correct Answer an enhancer in the gene encoding the HbF repressor, BCL11A Ricin directly inhibits: - Correct Answer translation The number of protons transferred from the matrix to the IMS as two electrons are transferred from UQH2 (ubiquinol) to oxidized soluble cytochrome c is: - Correct Answer 2 *asking about complex 3 specifically The redox active group of NAD+ and NADP+ is derived from what vitamin? - Correct Answer nicotinic acid The same gene gives rise to a protein of 200 amino acids in adipose cells but a protein of 180 amino acids in liver cells. Which of the following mechanisms most likely accounts for this difference? - Correct Answer alternative splicing Vitamin D can be produced by the action of sunlight on 7-dehydrocholesterol in the skin, but it has to be converted to its biologically active form by hydroxylation reactions in which of the following tissues? - Correct Answer liver and kidneys Which of the following statements is TRUE about the insulin receptor (IR)? - Correct Answer IR is a heterotetramer composed of two alpha and two beta subunits. What provides the most convincing evidence for oxidative damage in a tissue? - Correct Answer Detection of higher than normal levels of carbonylated (aldehyde- modified) protein Which of the following will most increase the fluidity of a cytoplasmic membrane? A: Close packing of saturated fatty acid tails B: Higher than normal levels of cholesterol C: An increase in fatty acid tails containing cis-double bonds D: An increase in glycosylated lipids E: The association of water with membrane surfaces - Correct Answer An increase in fatty acid tails containing cis-double bonds Which of the following is a universal characteristic of the alternating access mechanism of integral membrane transporters? - Correct Answer The mechanism avoids a conformer that opens a continuous pore across the membrane. What is part of the octameric structural core around which DNA is wrapped? - Correct Answer H2A H2B H3 H4 Which of the following diseases is caused by a trinucleotide repeat that induces heterochromatin? - Correct Answer fragile X syndrome Which of the following is an important cell cycle component that activates Cdks AND directs phosphorylation of specific target proteins? A: cyclin B: p53 C: Rb D: Wee 1 kinase E: Cdc 25 phosphatase - Correct Answer cyclin Which of the following enzymes is INACTIVATED by phosphorylation? A: glycogen phosphorylase B: glycogen phosphorylase kinase C: phosphofructokinase 1 D: phosphoenolpyruvate carboxykinase E: pyruvate dehydrogenase - Correct Answer pyruvate dehydrogenase Which of the following single step reactions occurs in both the cytoplasm and the mitochondrial matrix? A: Oxaloacetate --> malate B: Pyruvate --> phosphoenolpyruvate C: Malonyl CoA --> acetyl CoA + CO2 D: Pyruvate --> lactate E: Pyruvate --> acetyl CoA + CO2 - Correct Answer Oxaloacetate --> malate What are the gene silencing diseases? - Correct Answer Gene silencing is so MF Fine M - myotonic dystrophy F - friedreich ataxia F - Fragile X What are the DNA repair diseases? - Correct Answer DNA repair is LAX L - lynch syndrome A - atelengectasia X - xeroderma pigmentosa What inhibits the polymerase in eukaryotes that produces pre-mRNA? - Correct Answer alpha amanitin In response to DNA damage, which of the following promotes transcription of the gene encoding the Cdk inhibitor protein p21? - Correct Answer p53 You identify a new genetic disease and observe that patients with this disease have an expanded trinucleotide repeat (TNR) in a certain gene compared to unaffected individuals. This TNR is in the 3' UTR of the gene. Based on this information, you predict that the TNR mutation will result in: - Correct Answer altered half-life of the encoded mRNA In the presence of ADP and phosphate, proton flow through Fo of ATP synthase is MOST DIRECTLY driven by - Correct Answer the attraction of protons toward negative charge Which of the following occurs immediately upon the activation of uncoupling protein 1 in brown fat mitochondria? - Correct Answer The gamma subunit of ATP synthase rotates more slowly Hydrated Na+ does not easily move through a lipid bilayer by passive diffusion, but it does happen at a slow rate. Which of the following components of the cytoplasmic membrane MOST impedes the passive diffusion of hydrated Na+ across the membrane? - Correct Answer cholesterol A globular, multi-pass integral membrane protein in the cytoplasmic membrane is LEAST likely to have: A: Positively charged amino acid side chains on a surface exposed to the cytoplasm. B: Glycosylated amino acid side chains on its extracellular surface. C: Negatively charged amino acid side chains extending into the lipid bilayer. D: A transmembrane alpha helix with no direct contact with the lipid bilayer. E: An alpha helix containing 22 amino acids. - Correct Answer Negatively charged amino acid side chains extending into the lipid bilayer Hyaluronan is: - Correct Answer in the form of a watery gel In an adult human being, collagen fibrils: - Correct Answer Contain cross-links between mature collagen molecules. Over-the-counter drugs, such as Nexium and Prevacid, are one treatment for acid reflux disease. These drugs inhibit which of the following? - Correct Answer A H+/K+ antiport, a P-type ATPase Which of the following proteins involved in transport has a transmembrane domain that does not bind solute or undergo the conformational changes of the alternating access mechanism? - Correct Answer acetylcholine receptor The electrical potential (membrane potential) maintained by the Na+/K+ pump: - Correct Answer Favors the entry of all cations The substrates of the reaction catalyzed by glutathione peroxidase are H2O2 + 2GSH (reduced glutathione). The products in a balanced equation of the reaction are: - Correct Answer 2H2O + GSSG Type 1 diabetics, prior to diagnosis, display polydipsia, polyuria, and polyphagia. The polyuria is due to what? - Correct Answer Osmotic imbalance due to elevated glucose in urine Relative or absolute lack of insulin in humans would result in which of the following reactions in the liver? - Correct Answer increased oxidation fatty acids The individual in the attached figure suffered from a disease caused by a point mutation in the gene encoding a protein associated with which intracellular structure? - Correct Answer nuclear lamina Carbs = protein = calories? fats = ? alcohol = ? - Correct Answer 4 calories 9 calories 7 calories A healthy adult eats a balanced meal after a 16-hour fast. One hour later, which of the following enzymes would be LESS active than it was just prior to eating? A: Citrate lyase B: Glycogen synthase a C: Lipoprotein lipase D: Malic enzyme E: Pyruvate carboxylase - Correct Answer Pyruvate carboxylase pyruvate carboxylase - Correct Answer pyruvate to oxaloacetate Which of the following is DIRECTLY INACTIVATED by phosphorylation by active protein kinase A? - Correct Answer pyruvate kinase Does glycerol-3-phosphate dehydrogenase help convert alanine to glucose? - Correct Answer no What enzymes are required for the conversion of alanine to glucose? - Correct Answer - Fructose 1,6 bisphosphatase (FBP-1) Glucose 6-phosphatase Phosphoenolpyruvate carboxykinase -Pyruvate carboxylase Individuals with Hereditary Fructose Intolerance are counselled to avoid excess fructose and sucrose in the diet. For which of the following would the same advice apply? - Correct Answer Glycogen Storage Disease Type 1 (Von Gierke Disease) thiamin - Correct Answer Vitamin B1 What enzymes use B1 (thiamin)? - Correct Answer - ˞ketoglutarate dehydrogenase Branched chain ˞alpha keto acid dehydrogenase Lactate dehydrogenase Pyruvate dehydrogenase -Transketolase The presence of dicarboxylic acids in the urine is MOST LIKELY indicative of a defect in which of the following pathways? - Correct Answer U-oxidation of fatty acids During the fed state, fatty acids are synthesized in the liver from carbohydrates in excess of what can be stored in glycogen. Which of the following prevents these newly synthesized fatty acids from being oxidized (which would constitute a futile cycle)? - Correct Answer : Inhibition of CPT1 by malonyl CoA Which of the following is a precursor of eicosinoids? - Correct Answer Arachidonic acid An infant boy becomes lethargic 24 hours after birth. Blood tests reveal an elevated plasma ammonia concentration (160 µMol/L), normal blood glucose levels and a normal anion gap. Analysis of plasma amino acids reveals lower than normal levels of arginine and citrulline. Further tests revealed normal levels of urinary orotic acid. This individual MOST LIKELY has a deficiency in which of the following? - Correct Answer N-Acetylglutamate synthase