Category: Molecular Biology

trial 4 0

Case details- VNTR Analysis

A 16-year-old girl was abducted when she went to a local store. Her body was found the next morning and the autopsy revealed that she had been sexually assaulted and strangled. Crime scene investigators were able to collect a semen sample from vaginal fluid as well as tissue samples from underneath the victim’s fingernails. DNA samples were obtained from three suspects besides the victim. A variable number of tandem repeats (VNTR) analysis was performed on the DNA samples from the evidence collected, the victim, and the suspect and the results were compared. Which of the following techniques is the most...

trial 4 0

Cloning

A clone is a population of identical organisms derived from a single parental organism. In Molecular biology- A clone is a collection of molecules or cells, all identical to an original molecule or cell. If the original cells harbored a recombinant DNA molecule in the form of a plasmid, the plasmids within the millions of cells in a bacterial colony represent a clone of original DNA molecules; these molecules can be isolated and studied. The mechanism of cloning involves , i) Cutting DNA at precise locations, ii) Joining two DNA fragments covalently, iii) Selection of a small molecule of DNA...

trial 4 0

DNA Repair

The fidelity of replication is very high, with an overall error rate of 10-9 to 10-10. Insertion of an inappropriate nucleotide that occurs during replication can be corrected by editing during the replication process. This proof reading function is performed by a 3′-5′ exonuclease activity associated with the polymerase complex. The post replication repair process also increases the fidelity of replication. Which “one” of the following is not a post replication DNA repair mechanism? A. 5′-3′ – Exonuclease repair B. Base excision repair C. Mismatch repair D. Nucleotide excision repair E. Direct repair The answer is- A – 5′-3′ – Exonuclease repair....

trial 4 0

Frameshift mutations

Duchenne muscular dystrophy (DMD) is an X-linked disorder due to a frameshift mutation in the muscle protein “Dystrophin”. The patients have proximal muscle weakness and muscle fibrosis, with death occurring as a result of cardiac or respiratory failure. Which ‘one’ of the following statements correctly describes a frameshift mutation? A. The frameshift mutations occur due to substitution of the base analogs B. The reading frame beyond the mutation remains unaltered C. A frameshift mutation may not produce effects due to degeneracy of the genetic code D. Insertion or deletion of three nucleotides does not alter the reading frame beyond the...

trial 4 0

Splicing

The most common cause of β- Thalassemia is the defect in mRNA splicing of the beta globin gene. Mutations that affect the splicing create aberrant transcripts that are degraded before they are translated. If patients inherit a single mutated gene (thalassemia minor), the disease manifests with a mild anemia. However, patients with homozygous mutations (thalassemia major) have severe transfusion-dependent anemia. Which of the following types of RNA are involved in the splicing process? A. Ribosomal RNA (r RNA) B. Small nuclear RNA (sn RNA) C. Transfer RNA (t RNA) D. Small cytoplasmic RNA (sc RNA) E. Heterogeneous nuclear RNA (hn...

trial 4 0

Restriction enzymes and DNA fingerprinting

DNA fingerprinting is used in the legal world to determine parentage, genealogy, or other genetic relationships, or to implicate suspects in law enforcement investigations involving violent crimes. Fragments produced by various restriction enzymes from a number of different loci can be used to identify individuals with the accuracy of a fingerprint. Therefore, this technique is called “Fingerprinting”. Which “one” of the following statements is incorrect about restriction enzymes? A. They are site specific endonucleases B.  The restriction sites are palindrome in nature C. All restriction enzymes are of bacterial origin D. They always produce complementary single stranded overhangs E. They...

trial 4 0

Prokaryotes versus Eukaryotes

Case details A young man was brought to the emergency room after being hit by a car. His leg bone was broken in half, and the bone was protruding through the skin. He was recovering well after the orthopedic surgery. After several days he developed wound infection. The wound culture revealed a new bacterial organism that was resistant to all available antibiotics. The drugs acting as antibiotics specifically inhibit bacterial proliferation by inhibiting any of the processes such as replication, transcription or translation. Which of the following statements is exclusively true of prokaryotes but not of eukaryotes? A. Most of...

trial 4 0

Mechanism of action of Rifampin?

Case details A 37-year-old, female develops fever, night sweat, weight loss, and a blood- tinged cough. While in the emergency room, an infectious disease specialist is consulted, she is suspected to have pulmonary tuberculosis and is immediately prescribed with a multidrug regimen that includes rifampin (Figure). Rifampin inhibits RNA transcription because it inhibits the enzyme- A) DNA- dependent DNA polymerase B) DNA- dependent RNA polymerase C) RNA- dependent DNA polymerase D) RNA- dependent RNA polymerase E) Reverse transcriptase. Figure- Rifampin is widely used as an antitubercular drug. The correct answer is- B) DNA dependent RNA polymerase. DNA-dependent RNA polymerase is...

trial 4 0

RNA splicing

Case details A 45-year- old female of Indian origin reported for a routine checkup. She had no complaints and was in good health; however she reported a family history of anemia. Her complete blood count demonstrated mild anemia and the attending physician suspected thalassemia minor in the patient. Thalassemia is most often due to a defect in RNA splicing, which is best explained by which of the following statements? A) A high molecular weight precursor is trimmed to a short and mature m RNA. B) The coding regions found on the introns are rearranged and joined together. C) The introns...

trial 4 0

Mechanism of action of Ciprofloxacin

Case details A 38-year-old woman, who works as an administrative assistant for a large company, opened a package and found a suspicious white powder. Analysis of the powder indicates that it contained traces of the bacterium Bacillus anthracis. The woman was treated with ciprofloxacin, an effective antibiotic. Ciprofloxacin’s mechanism of action is best described as an inhibition of which of the following? A. Bacterial dihydrofolate reductase B. Bacterial peptidyl transferase activity C. Bacterial RNA polymerase D. DNA gyrase E. DNA polymerase III The correct answer is D- DNA gyrase. The quinolones, including nalidixic acid and its fluorinated derivatives (ciprofloxacin, levofloxacin,...

trial 4 0

Which of the following statements is correct regarding transcription?

CASE DETAILS A 4-year-old child, on a well-child- check up, is found to have a large flank mass. A computed tomography (CT) scan demonstrates a large mass arising from the kidney, and a subsequent biopsy reveals a diagnosis of Wilm’s tumor. A pediatric oncologist starts chemotherapy containing the transcription inhibitor Actinomycin D. Which of the following statements is correct regarding transcription? A. Eukaryotes often produce polycistronic mRNA B. RNA polymerase requires a primer C. The RNA chain grows in the 3′-5′ direction D. Rho factor is critical for the initiation of RNA transcription E. The TATA box contains a consensus...

trial 4 0

Nucleic acid with modified nucleotides

Case Details A second year medical student looking to match into a competitive residency joins a laboratory studying gene regulation in a mouse model of hepatocellular carcinoma. He isolates nucleic acids from the cells after exposure to a known carcinogen and has the sequence analyzed. He is surprised to find that some of the nucleotides are Pseudouridine and ribothymidine. Which type of nucleic acid has the student likely isolated? A. t RNA B. r RNA C. hn RNA D. m RNA E. sn RNA Answer- The correct answer is- A- t RNA. Transfer RNA s are post transcriptionally modified. Ribothymidine...

trial 4 0

Case study-Hemochromatosis

Case details A 53-year-old man sees his family physician with concerns that his skin is “bronzing”- Figure Figure- Bronze skin and diabetes, a sign of hemochromatosis He is found to have diabetes as well as an elevated ferritin (a sign of iron over load).The physician suspects hemochromatosis and finds the patient carries a mutation where tyrosine is substituted  for cysteine at position 282(C282Y) of the HFE gene. The patient is diagnosed with hemochromatosis, which is a disease that results from which type of mutation? A. Silent B. Missense C. Nonsense D. Frameshift E. Deletion Answer- The correct answer is B-...

trial 4 0

RNA editing in humans

Details A scientist is studying post -transcriptional processing in human stem cells. He clones an unknown segment of DNA to express the gene in culture. However when he sequences the protein, he finds that one of the amino acids does not match the amino acid that would be predicted from the genetic code. After confirmations, he suspects that RNA editing has taken place. Which of the following is an example of RNA editing in humans? A. Production of Calcitonin and Calcitonin related peptide from the same gene B. Production of membrane bound (m Ig M) and secreted (s IgM) from...

trial 4 0

Which of the following is not a characteristic of genetic code?

Which of the following is not a characteristic of genetic code? A. It is a triplet code B. It is non overlapping and without punctuation C. It is nearly universal D. It is degenerate – one code may code for more than one amino acid E. It is unambiguous Answer- The correct answer is D. Genetic code is degenerate, but that does not mean, a given code may code for more than one amino acids. In fact, multiple codons can decode the same amino acid, but vice versa is not true (figure) Genetic Code- Characteristics Specificity- Genetic code is specific...

trial 4 0

Case study- Pneumonia

Case details A 54-year-old man develops a productive cough and a low- grade fever. He visits his family physician who suspects mycoplasma pneumonia. The physician tries to treat the patient empirically with Erythromycin. Which of the following describes the mechanism of Erythromycin? A. Binds to 5′ cap of RNA B. Inhibits the 30S ribosomal RNA C. Binds to the Shine Dalgarno sequence D. Inhibits the initiation factor IF-1 E. Inhibits the 50 S ribosomal subunit. Answer- E-Inhibits the 50 S ribosomal subunit. Ribosomes are large complexes of protein and r RNA. They consist of two subunits one large (Heavy) and one...

trial 4 0

Case study – Urinary Tract infection

Case Details A 30-year-old female presents with burning on urination and blood in her urine. She is diagnosed with a urinary tract infection. She is prescribed an antibiotic that inhibits an enzyme that prevents extreme supercoiling of DNA. Super coiling of DNA results from unwinding at a replication fork. This enzyme breaks and rejoins DNA chains. Which of the following is the most characteristic of this enzyme? A. Helicase B. Single strand binding protein C. Topo isomerase D. DNA polymerase I E. DNA polymerase III Answer- The correct answer is C- Topoisomerase. The Supercoiling is controlled by a remarkable group...

trial 4 0

Case study- Mushroom poisoning ?

Case details Two couples present to the emergency room with severe nausea, vomiting and diarrhea. One of the patients admits that she served salad at the dinner party to which she had added a few mushrooms she picked on a hike earlier. With such information, it is likely that their symptoms are a result of inhibition of which molecular event?  A. Inhibition of RNA polymerase II B. Inhibition of RNA polymerase I C. Inhibition of RNA splicing D. Inhibition of RNA Polyadenylation E. Inhibition of RNA polymerase III Answer- The correct answer is RNA polymerase II. It is a case...

trial 4 0

Answer- Case study- HIV infection- A 33 -year-old, homosexual man..

Case details A 33 -year-old, homosexual man is recently diagnosed with human immuno deficiency virus (HIV) infection. His CD4+T- cell count is dramatically decreased, and he has a high HIV viral load. He is referred to an infectious disease clinic where they begin him on a nucleoside analog. These drugs inhibit DNA synthesis because they lack which of the following properties required for the normal DNA polymerization? A. 5′- phosphate B. 3′ – hydroxyl C. 7- methyl guanosine triphosphate D. Poly (A) tail E. A consensus sequence Answer- The correct option is B) – 3′-hydroxyl group .The replication proceeds with...

trial 4 0

Case study- HIV infection – A 33 -year-old, homosexual man is recently diagnosed..

Question of the day A 33 -year-old, homosexual man is recently diagnosed with human immuno deficiency virus (HIV) infection. His CD4+T- cell count is dramatically decreased, and he has a high HIV viral load.   Figure- A cross sectional view of HIV structure He is referred to an infectious disease clinic where they begin him on a nucleoside analog. These drugs inhibit DNA synthesis because they lack which of the following properties required for the normal DNA polymerization? A. 5′- phosphate B. 3′ – hydroxyl C. 7- methyl Guanosine triphosphate D. Poly (A) tail E. A consensus sequence For answer...

trial 4 0

Answer- Case study- DNA Replication- A scientist is replicating human DNA in a test tube…

A scientist is replicating human DNA in a test tube and has added intact DNA, the replisome complex, and the four deoxyribonucleoside triphosphates. To the surprise of the scientist, there was no DNA synthesized, as determined by the incorporation of radio-labeled precursors into acid-precipitable material. The scientist’s failure to synthesize DNA is most likely due to a lack of which of the following in his reaction mixture? A. Reverse transcriptase B. Ribonucleoside triphosphates C. Templates D. Dideoxynucleoside triphosphates E. Sigma factor The answer is B: Ribonucleoside triphosphates. DNA Replication is the basis for inheritance. It is the fundamental process occurring in...

trial 4 2

Case study- Replication-A scientist is replicating human DNA in a test tube ..

QUESTION OF THE DAY A scientist is replicating human DNA in a test tube and has added intact DNA, the replisome complex, and the four deoxyribonucleoside triphosphates.   Figure- DNA Replication To the surprise of the scientist, there was no DNA synthesized, as determined by the incorporation of radio-labeled precursors into acid-precipitable material. The scientist’s failure to synthesize DNA is most likely due to a lack of which of the following in his reaction mixture? A. Reverse transcriptase B. Ribonucleoside triphosphates C. Templates D. Dideoxynucleoside triphosphates E. Sigma factor For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-dna-replication-a-scientist-is-replicating-human-dna-in-a-test-tube/ Please help Biochemistry for Medics...

trial 4 0

Answer- DNA Structure-A sample of human DNA is subjected to increasing temperature

QUESTION A sample of human DNA is subjected to increasing temperature until the major fraction exhibits optical density changes due to disruption of its helix (melting or denaturation). A smaller fraction is atypical in that it requires a much higher temperature for melting. This smaller, atypical fraction of DNA must contain a higher content of A. Adenine plus Cytosine B. Cytosine plus Guanine C. Adenine plus Thymine D. Cytosine plus Thymine E. Adenine plus Guanine Answer-The answer is- B- Cytosine plus Guanine. Deoxyribonucleic acid (DNA) is the chemical basis of heredity and is organized into genes, the fundamental units of...

trial 4 2

Question of the day- DNA structure

A sample of human DNA is subjected to increasing temperature until the major fraction exhibits optical density changes due to disruption of its helix (melting or denaturation). A smaller fraction is atypical in that it requires a much higher temperature for melting. This smaller, atypical fraction of DNA must contain a higher content of A. Adenine plus Cytosine B. Cytosine plus Guanine C. Adenine plus Thymine D. Cytosine plus Thymine E. Adenine plus Guanine Figure- DNA Structure For answer follow the link http://usmle.biochemistryformedics.com/answer-dna-structure-a-sample-of-human-dna-is-subjected-to-increasing-temperature/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

Copy Protected by Chetan's WP-Copyprotect.