Trimethoprim inhibits bacteria without affecting mammalian cells because: A. It does not penetrate mammalian cells B. It has high affinity for bacterial but low affinity for mammalian dihydrofolate reductase enzyme C. It inhibits bacterial folate synthetase as well as dihydrofolate reductase enzymes D. All of the above

Trimethoprim inhibits bacteria without affecting mammalian cells because:
A. It does not penetrate mammalian cells
B. It has high affinity for bacterial but low
affinity for mammalian dihydrofolate reductase enzyme
C. It inhibits bacterial folate synthetase as well
as dihydrofolate reductase enzymes
D. All of the above
by

1 Answer

Answer :

B. It has high affinity for bacterial but low
affinity for mammalian dihydrofolate reductase enzyme
by

Related questions

Cancer cells may become resistant to amethopterin by (A) Developing mechanisms to destroy amethopterin (B) Amplification of dihydrofolate reducatse gene (C) Mutation in the dihydrofolate reductase gene so that the enzyme is no longer inhibited by amethopterin (D) Developing alternate pathway of thymidylate synthesis

Description : Cancer cells may become resistant to amethopterin by (A) Developing mechanisms to destroy amethopterin (B) Amplification of dihydrofolate reducatse gene (C) Mutation in the dihydrofolate reductase ... is no longer inhibited by amethopterin (D) Developing alternate pathway of thymidylate synthesis

Last Answer : Answer : B

Mammalian cells are not inhibited by low concentrations of tetracyclines that inhibit sensitive microorganisms because: A. Host cells lack active transport mechanism for tetracyclines B. Host cells actively pump out tetracyclines C. Protein synthesizing apparatus of host cells has low affinity for tetracyclines D. Both ‘A’ and ‘C’ are correct

Description : Mammalian cells are not inhibited by low concentrations of tetracyclines that inhibit sensitive microorganisms because: A. Host cells lack active transport mechanism for tetracyclines B. Host cells actively pump out ... host cells has low affinity for tetracyclines D. Both A' and C' are correct

Last Answer : D. Both ‘A’ and ‘C’ are correct

Methotrexate blocks the synthesis of thymidine monophosphate by inhibiting the activity of the enzyme: (A) Dihydrofolate reductase (B) Orotate phosphoribosyl transferase (C) Ribonucleotide reductase (D) Dihydroorotase

Description : Methotrexate blocks the synthesis of thymidine monophosphate by inhibiting the activity of the enzyme: (A) Dihydrofolate reductase (B) Orotate phosphoribosyl transferase (C) Ribonucleotide reductase (D) Dihydroorotase

Last Answer : Answer : A

In biosynthesis of cholesterol triparanol inhibits the activity of the enzyme: (A) ∆24 Reductase (B) Oxidosqualene-lanosterol cyclase (C) Isomerase (D) Squalene epoxidase ENZYMES 155

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Last Answer : Answer : A

Ethanol is used in methanol poisoning because it: A. Antagonises the actions of methanol B. Stimulates the metabolism of methanol and reduces its blood level C. Inhibits the metabolism of methanol and generation of toxic metabolite D. Replenishes the folate stores depleted by methano

Description : Ethanol is used in methanol poisoning because it: A. Antagonises the actions of methanol B. Stimulates the metabolism of methanol and reduces its blood level C. Inhibits the metabolism of methanol and generation of toxic metabolite D. Replenishes the folate stores depleted by methano

Last Answer : C. Inhibits the metabolism of methanol and generation of toxic metabolite

Amplification of dihydrofolate reductase gene may be brought about by (A) High concentrations of folic acid (B) Deficiency of folic acid (C) Low concentration of thymidylate (D) Amethopterin

Description : Amplification of dihydrofolate reductase gene may be brought about by (A) High concentrations of folic acid (B) Deficiency of folic acid (C) Low concentration of thymidylate (D) Amethopterin

Last Answer : Answer : D

A patient of megaloblastic anaemia was treated with oral folic acid 5 mg daily. After 2 weeks he reported back with cognitive deficit, sensory disturbance, depressed knee jerk, while blood picture and haemoglobin level were improved. What could be the most likely explanation: A. Folic acid was not adequately absorbed resulting in partial response B. Folate therapy has precipitated vitamin B12 deficiency in the neural tissue C. Folate therapy has unmasked pyridoxine deficiency D. Patient has folate reductase abnormality in the nervous system

Description : A patient of megaloblastic anaemia was treated with oral folic acid 5 mg daily. After 2 weeks he reported back with cognitive deficit, sensory disturbance, depressed knee jerk, while ... therapy has unmasked pyridoxine deficiency D. Patient has folate reductase abnormality in the nervous system

Last Answer : D. Patient has folate reductase abnormality in the nervous system

Cholesterol by a feed back mechanism inhibits the activity of (A) HMG-CoA synthetase (B) HMG-CoA reductase (C) Thilase (D) Mevalonate kinase

Description : Cholesterol by a feed back mechanism inhibits the activity of (A) HMG-CoA synthetase (B) HMG-CoA reductase (C) Thilase (D) Mevalonate kinase

Last Answer : Answer : B

An enzyme required for the synthesis of ketone bodies as well as cholesterol is (A) Acetyl CoA carboxylase (B) HMG CoA synthetase (C) HMG CoA reductase (D) HMG CoA lyase

Description : An enzyme required for the synthesis of ketone bodies as well as cholesterol is (A) Acetyl CoA carboxylase (B) HMG CoA synthetase (C) HMG CoA reductase (D) HMG CoA lyase

Last Answer : Answer : B

The most important mechanism of bacterial resistance to an aminoglycoside antibiotic is: A. Plasmid mediated acquisition of aminoglycoside conjugating enzyme B. Mutational acquisition of aminoglycoside hydrolysing enzyme C. Mutation reducing affinity of ribosomal protein for the antibiotic D. Mutational loss of porin channels

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Last Answer : A. Plasmid mediated acquisition of aminoglycoside conjugating enzyme

Distinctive features of gatifloxacin include the following except: A. Higher affinity for the enzyme topoisomerase IV B. Activity restricted to gram negative bacteria C. Potential to prolong QTc interval D. Employed to treat community acquired pneumonia

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Last Answer : B. Activity restricted to gram negative bacteria

The following is true of linezolid except: A. It inhibits bacterial protein synthesis at an early step B. It is active against vancomycin resistant enterococci C. It is the drug of choice for enterococcal endocarditis D. It can be administered orally as well as by i.v. infusion

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Amplification of dihydrofolate reductase gene in a cancer cell makes the cell (A) Susceptible to folic acid deficiency (B) Less malignant (C) Resistant to amethopterin therapy (D) Responsive to amethopterin therapy

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Last Answer : Answer : C

Conversion of deoxyuridine monophosphate to thymidine monophosphate is catalysed by the enzyme: (A) Ribonucleotide reductase (B) Thymidylate synthetase (C) CTP synthetase (D) Orotidylic acid decarboxylase

Description : Conversion of deoxyuridine monophosphate to thymidine monophosphate is catalysed by the enzyme: (A) Ribonucleotide reductase (B) Thymidylate synthetase (C) CTP synthetase (D) Orotidylic acid decarboxylase

Last Answer : Answer : B

In the biosynthesis of cholesterol, the rate limiting enzyme is (A) Mevalonate kinase (B) HMG-CoA synthetase (C) HMG-CoA reductase (D) Cis-prenyl transferase

Description : In the biosynthesis of cholesterol, the rate limiting enzyme is (A) Mevalonate kinase (B) HMG-CoA synthetase (C) HMG-CoA reductase (D) Cis-prenyl transferase

Last Answer : Answer : C

Gram negative organisms are largely insensitive to benzyl penicillin because: A. They produce large quantities of penicillinase B. They do not utilise D-alanine whose incorporation in the cell wall is inhibited by benzylpenicillin C. Benzyl penicillin is not able to penetrate deeper into the lipoprotein-peptidoglycan multilayer cell wall of gram negative bacteria D. Both ‘A’ and ‘B’ are correct

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Last Answer : . Benzyl penicillin is not able to penetrate deeper into the lipoprotein-peptidoglycan multilayer cell wall of gram negative bacteria

The promoter on an expression vector used to overproduce proteins in bacteria is A.a bacterial promoter B.expressed both in bacteria and mammalian cells C.not a regulated promoterD.the natural promoter of the gene being cloned

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That sulfonamides act by inhibiting folate synthesis in bacteria is supported by the following findings except: A. Paraaminobenzoic acid antagonises the action of sulfonamides B. Methionine antagonises the action of sulfonamides C. Purines and thymidine present in pus antagonise the action of sulfonamides D. Bacteria that utilise folic acid taken up from the medium are insensitive to sulfonamides

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Aspirin in small doses (50 to 150 mg per day) (a) Is of benefit in patients of unstable angina (b) Has thrombolytic action (c) PREFerentially inhibits prostacyclin synthetase enzyme (d) MAY Alleviate need for Verapamil in variant angina

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The most important mechanism by which gram negative bacilli acquire chloramphenicol resistance is: A. Decreased permeability into the bacterial cell B. Acquisition of a plasmid encoded for chloramphenicol acetyl transferase C. Lowered affinity of the bacterial ribosome for chloramphenicol D. Switching over from ribosomal to mitochondrial protein synthesi

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Clavulanic acid is combined with amoxicillin because: A. It kills bacteria that are not killed by amoxicillin B. It retards renal excretion of amoxicillin C. It counteracts the adverse effects of amoxicillin D. It inhibits beta lactamases that destroy amoxicillin

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Last Answer : D. It inhibits beta lactamases that destroy amoxicillin

Conversion of testosterone to dihydrotestosterone by the enzyme 5α-reductase is required for the following actions except: A. Formation of male external genitalia in the foetus B. Prostatic hypertrophy in elderly males C. Pubertal changes in the male adolescent D. Spermatogenesis

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Last Answer : D. Spermatogenesis

Select the antibiotic which inhibits bacterial protein synthesis by interfering with translocation of elongating peptide chain from acceptor site back to the peptidyl site of the ribosome so that ribosome does not move along the mRNA and the peptide chain is prematurely terminated: A. Chloramphenicol B. Erythromycin C. Tetracycline D. Streptomycin

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Chloramphenicol inhibits bacterial protein synthesis by: A. Binding to 30S ribosome and inhibiting attachment of aminoacyl tRNA B. Binding to 50S ribosome and preventing peptide bond formation C. Binding to 50S ribosome and blocking translocation of peptide chain D. Binding to both 30S and 50S ribosome and inducing misreading of mRNA code

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Last Answer : B. Binding to 50S ribosome and preventing peptide bond formation

Aspirin in low doses produces longlasting inhibition of platelet cyclooxygenase (COX) because: A. Platelets contain low quantity of COX B. Platelets cannot synthesize fresh COX molecules C. Platelets bind aspirin with high affinity D. Platelet COX is inducible

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Last Answer : B. Platelets cannot synthesize fresh COX molecules

Indicate the condition in which neither trimethoprim nor sulfamethoxazole alone are effective, but their combination cotrimoxazole is: A. Prostatitis B. Lymphogranuloma venereum C. Pneumocystis carinii pneumonia D. Bacillary dysentery

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Last Answer : C. Pneumocystis carinii pneumonia

he following antidiabetic drug inhibits intestinal brush border α-glucosidase enzymes: A. Acarbose B. Pioglitazone C. Metformin D. Guargum

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Omeprazole exerts practically no other action except inhibition of gastric acid secretion because: A. It transforms into the active cationic forms only in the acidic pH of the gastric juice B. Its active forms have selective affinity for the H+K+ATPase located in the apical canaliculi of gastric parietal cells C. Its cationic forms are unable to diffuse out from the gastric parietal cell canaliculi D. All of the above

Description : Omeprazole exerts practically no other action except inhibition of gastric acid secretion because: A. It transforms into the active cationic forms only in the acidic pH of the gastric juice B. Its ... forms are unable to diffuse out from the gastric parietal cell canaliculi D. All of the above

Last Answer : D. All of the above

The most common mechanism of development of resistance to fluoroquinolones is: A. Chromosomal mutation altering affinity of target site B. Plasmid transfer C. Acquisition of drug destroying enzyme D. Acquisition of alternative metabolic pathway

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Microsomal enzyme induction has one of the following features: A. Takes about one week to develop B. Results in increased affinity of the enzyme for the substrate C. It is irreversible D. Can be used to treat acute drug poisonings

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Last Answer : A. Takes about one week to develop

The plasma half life of penicillin-G is longer in the new born because their: A. Plasma protein level is low B. Drug metabolizing enzymes are immature C. Glomerular filtration rate is low D. Tubular transport mechanisms are not well developed

Description : The plasma half life of penicillin-G is longer in the new born because their: A. Plasma protein level is low B. Drug metabolizing enzymes are immature C. Glomerular filtration rate is low D. Tubular transport mechanisms are not well developed

Last Answer : D. Tubular transport mechanisms are not well developed

Methicillin resistant staphylococci do not respond to β-lactam antibiotics because: A. They produce a β-lactamase which destroys methicillin and related drugs B. They elaborate an amidase which destroys methicillin and related drugs C. They have acquired penicillin binding protein which has low affinity for β-lactam antibiotics D. They are less permeable to β-lactam antibiotics

Description : Methicillin resistant staphylococci do not respond to β-lactam antibiotics because: A. They produce a β-lactamase which destroys methicillin and related drugs B. They elaborate an amidase which destroys ... low affinity for β-lactam antibiotics D. They are less permeable to β-lactam antibiotics

Last Answer : C. They have acquired penicillin binding protein which has low affinity for β-lactam antibioti

Digitalis in creases the force of contraction of ventricles by: A. Increasing the duration of systole B. Increasing the rate of contraction without affecting the duration of systole C. Increasing the rate of contraction, but reducing the duration of systole D. Increasing both the rate of contraction as well as the duration of systole

Description : Digitalis in creases the force of contraction of ventricles by: A. Increasing the duration of systole B. Increasing the rate of contraction without affecting the duration of systole C. Increasing the rate ... of systole D. Increasing both the rate of contraction as well as the duration of systole

Last Answer : C. Increasing the rate of contraction, but reducing the duration of systole

Trimethoprim is combined with sulfamethoxazole in a ratio of 1:5 to yield a steady state plasma concentration ratio of: A. Trimethoprim 1: Sulfamethoxazole 5 B. Trimethoprim 1: Sulfamethoxazole 10 C. Trimethoprim 1: Sulfamethoxazole 20 D. Trimethoprim 5: Sulfamethoxazole 1

Description : Trimethoprim is combined with sulfamethoxazole in a ratio of 1:5 to yield a steady state plasma concentration ratio of: A. Trimethoprim 1: Sulfamethoxazole 5 B. Trimethoprim 1: Sulfamethoxazole 10 C. Trimethoprim 1: Sulfamethoxazole 20 D. Trimethoprim 5: Sulfamethoxazole 1

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Select the drug combination which does not exhibit supraadditive synergism: A. Nalidixic acid + Nitrofurantoin B. Amoxicillin + Clavulanic acid C. Pyrimethamine + Sulfadoxine D. Sulfamethoxazole + Trimethoprim

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Last Answer : A. Nalidixic acid + Nitrofurantoin

Which of the following is a potassium retaining diuretic: A. Triamterene B. Trimethoprim C. Tizanidine D. Trimetazidine

Description : Which of the following is a potassium retaining diuretic: A. Triamterene B. Trimethoprim C. Tizanidine D. Trimetazidine

Last Answer : A. Triamterene

Select the drug that reversibly inhibits the enzyme COMT and is useful as an adjuvant medication in advanced parkinson's disease: A. Pramipexole B. Entacapone C. Pergolide D. Piribedil

Description : Select the drug that reversibly inhibits the enzyme COMT and is useful as an adjuvant medication in advanced parkinson's disease: A. Pramipexole B. Entacapone C. Pergolide D. Piribedil

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The following is true of topiramate except: A. It is a broad spectrum antiepileptic drug B. It inhibits the enzyme carbonic anhydrase C. It is used as add-on therapy in refractory partial seizures D. It is not effective in generalized tonic-clonic seizures

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Last Answer : D. It is not effective in generalized tonic-clonic seizures

Hydrocortisone induces the synthesis of the following protein which in turn inhibits the enzyme phospholipase-A2: A. Heat shock protein-90 B. Inhibin C. Transcortin D. Lipocortin

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Last Answer : D. Lipocortin

Choose the correct statement about bambuterol: A. It is an orally acting bronchodilator B. It is a prodrug C. It inhibits the enzyme pseudocholinesterase D. All of the above

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Which of the following is a disease modifying antirheumatic drug whose active metabolite inhibits the enzyme dihydro-orotate dehydrogenase: A. Leflunomide B. Nimesulide C. Sulfasalazine D. Colchicine

Description : Which of the following is a disease modifying antirheumatic drug whose active metabolite inhibits the enzyme dihydro-orotate dehydrogenase: A. Leflunomide B. Nimesulide C. Sulfasalazine D. Colchicine

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Hyperargininemia, a defect in urea synthesis develops due to deficiency of the enzyme: (A) Ornithine transcarbamoylase (B) Argininosuccinase (C) Arginase (D) Argininosuccinate synthetase ENZYMES 157

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Last Answer : Answer : B

The following is correct about antipsychotic drugs except: A. They only control symptoms of schizophrenia without affecting the basic disorder B. Combination of two or more antipsychotic drugs is more efficacious than any single drug C. In treating psychosis high potency drugs are preferred over low potency drugs D. They donot produce dependence

Description : The following is correct about antipsychotic drugs except: A. They only control symptoms of schizophrenia without affecting the basic disorder B. Combination of two or more antipsychotic drugs is ... psychosis high potency drugs are preferred over low potency drugs D. They donot produce dependence

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The most important mechanism of bacterial resistance to an aminoglycoside antibiotic is (a) Plasmid mediated acquisition of aminoglycoside conjugating enzyme (b) Mutational acquisition of aminoglycoside hydrolyzing enzyme (c) Mutation reducing affinity of ribosomal protein for the antibiotic (d) Mutational loss of porin channels

Description : The most important mechanism of bacterial resistance to an aminoglycoside antibiotic is (a) Plasmid mediated acquisition of aminoglycoside conjugating enzyme (b) Mutational acquisition of aminoglycoside ... affinity of ribosomal protein for the antibiotic (d) Mutational loss of porin channels

Last Answer : Ans: A

Compared to older tetracyclines, doxycycline produces a lower incidence of superinfection diarrhoea because: A. It is completely absorbed in the small intestines so that drug concentration in the colonic contents is low B. It is inactivated by the gut microflora C. It is not active against the microbes of the normal gut flora D. It is a potent tetracycline and inhibits

Description : Compared to older tetracyclines, doxycycline produces a lower incidence of superinfection diarrhoea because: A. It is completely absorbed in the small intestines so that drug concentration in the colonic contents ... the microbes of the normal gut flora D. It is a potent tetracycline and inhibits

Last Answer : A. It is completely absorbed in the small intestines so that drug concentration in the colonic contents is low

The following is true for gentamicin: A. It is more active in acidic medium B. It has a wide margin of safety C. It is excreted unchanged, mainly by glomerular filtration D. It primarily inhibits gram positive bacteria

Description : The following is true for gentamicin: A. It is more active in acidic medium B. It has a wide margin of safety C. It is excreted unchanged, mainly by glomerular filtration D. It primarily inhibits gram positive bacteria

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What is true of cefpirome: A. It is a fourth generation cephalosporin B. It easily penetrates porin channels of gram negative bacteria C. It inhibits type I β-lactamase producing enterobacteriaceae D. All of the above

Description : What is true of cefpirome: A. It is a fourth generation cephalosporin B. It easily penetrates porin channels of gram negative bacteria C. It inhibits type I β-lactamase producing enterobacteriaceae D. All of the above

Last Answer : . All of the above

Select the antimetabolite which is toxic to Leishmania but not to mammalian cells: A. Allopurinol B. Cytarabine C. 6-Mercaptopurine D. 6-Thioguanine

Description : Select the antimetabolite which is toxic to Leishmania but not to mammalian cells: A. Allopurinol B. Cytarabine C. 6-Mercaptopurine D. 6-Thioguanine

Last Answer : A. Allopurino

Antibacterial agents can be classified with regard to their structure, mechanism of action, and activity pattern against various types of bacterial pathogens. Which of the following statement(s) is/are true concerning antimicrobial classes? a. Penicillins and cephalosporins share the compound structure of a b-lactam ring which binds to bacterial division plate proteins b. Tetracyclines and macrolides such as erythromycin inhibit bacterial ribosomal activity and therefore protein synthesis c. Aminoglycosides act in a similar fashion to tetracyclines and therefore are both bacteriostatic d. Sulfonamides and trimethoprim act synergistically to inhibit purine synthesis

Description : Antibacterial agents can be classified with regard to their structure, mechanism of action, and activity pattern against various types of bacterial pathogens. Which of the following ... are both bacteriostatic d. Sulfonamides and trimethoprim act synergistically to inhibit purine synthesis

Last Answer : Answer: a, b, d Penicillins, cephalosporins, and monobactams possess a b-lactam ring of some type and act to bind bacterial division plate proteins, thus inhibiting cell wall ... act in different mechanisms to inhibit protein synthesis, therefore two agents in combination act synergistically

HMG-CoA is converted to mevalonate by reduction catalysed by (A) HMG-CoA synthetase (B) HMG-CoA reductase (C) Mevalonate kinase (D) Thiolase

Description : HMG-CoA is converted to mevalonate by reduction catalysed by (A) HMG-CoA synthetase (B) HMG-CoA reductase (C) Mevalonate kinase (D) Thiolase

Last Answer : Answer : B