Transcription: RNA Synthesis — MCQs
In E. coli, Arthur Kornberg found which enzyme?
Which RNA modification at the 3' end stabilizes mRNA by preventing exonuclease degradation?
A lady gets pregnant even though she was on contraceptive pills. She is suspected to have consumed
Match the following drugs in Column A with their contraindications in Column B. | Column A | Column B | | :-- | :-- | | 1. Morphine | 1. QT prolongation | | 2. Amiodarone | 2. Thromboembolism | | 3. Vigabatrin | 3. Pregnancy | | 4. Estrogen preparations | 4. Head injury |
Steps in review of patient's history during secondary survey of trauma care can be summarised as
Which of the following statements about Taq DNA polymerase is correct?
What sequence on the template strand of DNA corresponds to the first amino acid inserted into a protein?
Inosinic acid is biological precursor of ?
Consider the following statements regarding folic acid : 1. It is needed for normal development of blood cells in the marrow. 2. It has a role in the synthesis of nucleic acids. 3. It is resistant to boiling. Which of the statements given above is/are correct?
False statements are:
Transcription: RNA Synthesis Indian Medical PG Practice Questions and MCQs
Question 1: In E. coli, Arthur Kornberg found which enzyme?
- A. DNA polymerase (Correct Answer)
- B. Glucose 6 phosphate dehydrogenase
- C. Fatty acid synthase
- D. Topoisomerase
Explanation: ***DNA polymerase*** - Arthur Kornberg was awarded the Nobel Prize in Physiology or Medicine in 1959 for his discovery of **DNA polymerase I** in *Escherichia coli*. - This enzyme is crucial for **DNA replication and repair** in bacteria, catalyzing the synthesis of new DNA strands. *Fatty acid synthase* - This enzyme complex is responsible for the **biosynthesis of fatty acids** in living organisms. - While essential for *E. coli*, its discovery is not attributed to Arthur Kornberg. *Glucose 6 phosphate dehydrogenase* - This enzyme is key in the **pentose phosphate pathway**, producing NADPH and ribose-5-phosphate. - It is critical for cellular metabolism but was not the enzyme discovered by Kornberg. *Topoisomerase* - Topoisomerases are enzymes that regulate the **supercoiling of DNA** by transiently breaking and rejoining DNA strands. - Their discovery postdates Kornberg's work on DNA polymerase.
Question 2: Which RNA modification at the 3' end stabilizes mRNA by preventing exonuclease degradation?
- A. Polyadenylation (Correct Answer)
- B. Capping
- C. Splicing
- D. Methylation
Explanation: ***Polyadenylation*** - The addition of a **poly-A tail** (a long chain of adenine nucleotides) to the **3' end** of mRNA is the primary modification that protects it from degradation by **3' to 5' exonucleases**. - This tail also plays crucial roles in mRNA export from the nucleus, translation initiation, and determining mRNA half-life. - The poly-A tail is progressively shortened by deadenylases, and once critically shortened, the mRNA becomes susceptible to degradation. *Capping* - **5' capping** involves the addition of a **7-methylguanosine cap** to the **5' end** of mRNA. - While this protects mRNA from **5' to 3' exonuclease** degradation, the question specifically asks about the **3' end** modification, which is polyadenylation. - The cap structure is also essential for ribosome binding and translation initiation. *Splicing* - **Splicing** is the process of removing **introns** (non-coding regions) and joining **exons** (coding regions) in pre-mRNA. - Its main function is to produce a mature mRNA sequence that can be translated into a functional protein, not to directly prevent exonuclease degradation. *Methylation* - **Methylation** can occur on various nucleotides within RNA molecules (e.g., N6-methyladenosine or m6A). - While methylation can influence mRNA stability, translation efficiency, and splicing, it is primarily a regulatory modification rather than a direct structural protection against exonuclease degradation like polyadenylation.
Question 3: A lady gets pregnant even though she was on contraceptive pills. She is suspected to have consumed
- A. Ciprofloxacin
- B. Rifampicin (Correct Answer)
- C. Streptomycin
- D. None of these
Explanation: ***Rifampicin*** - **Rifampicin** is a potent inducer of **hepatic microsomal enzymes** (cytochrome P450 enzymes), particularly CYP3A4. - This enzyme induction leads to increased metabolism and thus decreased effectiveness of **oral contraceptive pills**, raising the risk of unintended pregnancy. *Ciprofloxacin* - **Ciprofloxacin** is a **quinolone antibiotic** that primarily works by inhibiting bacterial DNA gyrase and topoisomerase IV. - It does not significantly induce hepatic enzymes or interfere with the efficacy of **oral contraceptive pills**. *Streptomycin* - **Streptomycin** is an **aminoglycoside antibiotic** that inhibits bacterial protein synthesis. - It is not known to have a significant drug interaction with **oral contraceptive pills** that would lead to contraceptive failure. *None of these* - This option is incorrect because **Rifampicin** is well-documented to reduce the effectiveness of **oral contraceptive pills**.
Question 4: Match the following drugs in Column A with their contraindications in Column B. | Column A | Column B | | :-- | :-- | | 1. Morphine | 1. QT prolongation | | 2. Amiodarone | 2. Thromboembolism | | 3. Vigabatrin | 3. Pregnancy | | 4. Estrogen preparations | 4. Head injury |
- A. A-1, B-3, C-2, D-4
- B. A-4, B-1, C-3, D-2 (Correct Answer)
- C. A-3, B-2, C-4, D-1
- D. A-2, B-4, C-1, D-3
Explanation: ***A-4, B-1, C-3, D-2*** - **Morphine** is contraindicated in **head injury** as it can increase intracranial pressure and mask neurological symptoms. - **Amiodarone** is contraindicated in patients with **QT prolongation** due to its risk of inducing more severe arrhythmias like Torsades de Pointes. - **Vigabatrin** is contraindicated during **pregnancy** due to its potential for teratogenicity and adverse effects on fetal development. - **Estrogen preparations** are contraindicated in patients with a history of **thromboembolism** due to their increased risk of blood clot formation. *A-1, B-3, C-2, D-4* - This option incorrectly matches **Morphine** with QT prolongation and **Estrogen preparations** with head injury, which are not their primary contraindications. - It also incorrectly links **Vigabatrin** with thromboembolism and **Amiodarone** with pregnancy. *A-3, B-2, C-4, D-1* - This choice incorrectly associates **Morphine** with pregnancy and **Vigabatrin** with head injury, which are not the most critical or direct contraindications. - It also misaligns **Amiodarone** with thromboembolism and **Estrogen preparations** with QT prolongation. *A-2, B-4, C-1, D-3* - This option incorrectly matches **Morphine** with thromboembolism and **Amiodarone** with head injury, which are not their most significant contraindications. - It also incorrectly links **Vigabatrin** with QT prolongation and **Estrogen preparations** with pregnancy.
Question 5: Steps in review of patient's history during secondary survey of trauma care can be summarised as
- A. TRIAGE
- B. ABCDE
- C. AMPLE (Correct Answer)
- D. None of the options
Explanation: ***AMPLE*** - The **AMPLE history** is a mnemonic used during the **secondary survey** in trauma care to gather crucial patient information - It stands for **Allergies, Medications, Past medical history/Pregnancy, Last meal, and Events** surrounding the injury. *TRIAGE* - **Triage** is the process of prioritizing patients based on the severity of their condition and the likelihood of benefit from immediate treatment. - It is an initial assessment done to determine the urgency of care, not a detailed historical review for a single patient. *ABCDE* - The **ABCDE approach** (**Airway, Breathing, Circulation, Disability, Exposure**) is part of the **primary survey** in trauma care. - It focuses on identifying and managing immediate life-threatening conditions. *None of the options* - This option is incorrect because **AMPLE** specifically describes the historical review process during the secondary survey.
Question 6: Which of the following statements about Taq DNA polymerase is correct?
- A. Optimum temperature for chain elongation is 75°C (Correct Answer)
- B. Denatures at high temperatures
- C. Provides high fidelity during DNA synthesis
- D. Exhibits 3' to 5' exonuclease activity
Explanation: ***Optimum temperature for chain elongation is 75°C*** - **Taq polymerase** is a **thermostable enzyme** isolated from *Thermus aquaticus*, functioning optimally at high temperatures. - The optimal temperature for the **elongation step** in PCR, where Taq polymerase synthesizes new DNA strands, is typically around **72-78°C**, with 75°C falling within this optimal range. *Denatures at high temperatures* - While all proteins will eventually denature at extremely high temperatures, Taq polymerase is specifically known for its **thermostability** and **resistance to denaturation** at temperatures required for DNA strand separation in PCR (typically 94-98°C). - Its ability to withstand these high temperatures without significant loss of activity is its key advantage for use in **Polymerase Chain Reaction (PCR)**. *Provides high fidelity during DNA synthesis* - **Taq polymerase** is known for its relatively **low fidelity** due to the lack of 3' to 5' exonuclease activity (proofreading). - This low fidelity results in a higher error rate during DNA synthesis compared to other polymerases with proofreading capabilities, leading to more **mutations** during PCR. *Exhibits 3' to 5' exonuclease activity* - **Taq polymerase** typically **lacks 3' to 5' exonuclease activity**, meaning it does not have the ability to proofread and remove incorrectly incorporated nucleotides. - This absence of proofreading contributes to its relatively **lower fidelity** during DNA replication compared to other polymerases that possess this activity.
Question 7: What sequence on the template strand of DNA corresponds to the first amino acid inserted into a protein?
- A. 3' TAC 5' (Correct Answer)
- B. 3' TAG 5'
- C. 3' TAA 5'
- D. 3' ATG 5'
Explanation: ***3' TAC 5'*** - The **start codon** for protein synthesis on **mRNA** is **5'-AUG-3'**, which codes for **methionine** (or N-formylmethionine in prokaryotes) and signals the initiation of translation. - To produce an mRNA codon of **5'-AUG-3'**, the complementary sequence on the **template DNA strand** must be **3'-TAC-5'** (adenine pairs with uracil/thymine, guanine pairs with cytosine, and the strands are antiparallel). - During transcription, RNA polymerase reads the template strand in the 3' to 5' direction and synthesizes mRNA in the 5' to 3' direction. *3' TAG 5'* - This template DNA sequence would be transcribed to produce the mRNA codon **5'-AUC-3'**, which codes for **isoleucine**, not methionine. - Therefore, this sequence does not correspond to the first amino acid inserted into a protein. *3' TAA 5'* - This template DNA sequence would be transcribed to produce the mRNA codon **5'-AUU-3'**, which also codes for **isoleucine**, not methionine. - This is not the initiation codon sequence. *3' ATG 5'* - While **ATG** appears in this sequence, when presented as the **template strand** in the 3' to 5' orientation, it would be transcribed to produce mRNA **5'-UAC-3'**, which codes for **tyrosine**, not methionine. - The sequence **ATG** on the **coding strand** (non-template strand) corresponds to the start codon, but this option incorrectly presents it as the template strand sequence.
Question 8: Inosinic acid is biological precursor of ?
- A. Purines and thymine
- B. Orotic acid and uridylic acid
- C. Adenylic acid and guanylic acid (Correct Answer)
- D. Uracil and thymine
Explanation: ***Adenylic acid and guanylic acid*** - Inosinic acid (IMP) is a **key intermediate** in the **de novo purine synthesis pathway**. - It serves as the direct precursor for the synthesis of **adenylic acid (AMP)** and **guanylic acid (GMP)**, which are components of DNA and RNA. *Purines and thymine* - While inosinic acid is a precursor to purines, it is **not a precursor to thymine**. - Thymine is a **pyrimidine base** and is synthesized through a separate pathway. *Orotic acid and uridylic acid* - **Orotic acid** is an intermediate in **pyrimidine synthesis**, not purine synthesis. - **Uridylic acid (UMP)** is also a pyrimidine nucleotide, and its synthesis pathway involves orotic acid, not inosinic acid. *Uracil and thymine* - **Uracil** and **thymine** are pyrimidine bases, and their synthesis pathways are distinct from the purine synthesis pathway involving inosinic acid. - Inosinic acid is exclusively involved in the synthesis of **purine nucleotides**.
Question 9: Consider the following statements regarding folic acid : 1. It is needed for normal development of blood cells in the marrow. 2. It has a role in the synthesis of nucleic acids. 3. It is resistant to boiling. Which of the statements given above is/are correct?
- A. 2 and 3
- B. 1 and 2 (Correct Answer)
- C. 1 and 3
- D. 1 only
Explanation: ***Correct Answer: 1 and 2*** **Analysis of each statement:** **Statement 1: Folic acid is needed for normal development of blood cells in the marrow** - **CORRECT** - Folic acid is essential for **hematopoiesis** (blood cell formation) - Required for normal maturation of **red blood cells** and **white blood cells** - Deficiency leads to **megaloblastic anemia** due to impaired DNA synthesis in rapidly dividing cells **Statement 2: Folic acid has a role in synthesis of nucleic acids** - **CORRECT** - Acts as a coenzyme in **one-carbon transfer reactions** - Essential for synthesis of **purines** and **thymidylate** (required for DNA synthesis) - Critical for synthesis of both **DNA and RNA** - Particularly important in rapidly dividing cells **Statement 3: Folic acid is resistant to boiling** - **INCORRECT** - Folic acid is **heat-labile** and **water-soluble** - Destroyed by prolonged cooking and boiling - Up to **50-90% loss** can occur during cooking of vegetables - This is why fresh or lightly cooked vegetables are better sources of folate **Why other options are incorrect:** *Incorrect: 2 and 3* - While statement 2 is correct, statement 3 is false - folic acid is NOT resistant to boiling *Incorrect: 1 and 3* - While statement 1 is correct, statement 3 is false - folic acid is heat-sensitive *Incorrect: 1 only* - Statement 2 is also correct - folic acid plays a fundamental role in nucleic acid synthesis
Question 10: False statements are:
- A. DNA replication proceeds in one direction
- B. Lagging strand is synthesized by RNA primase
- C. All of the options (Correct Answer)
- D. Bacteria have multiple origins of replication
Explanation: ***All of the options*** - All statements are **false**. DNA replication proceeds **bidirectionally**, bacteria typically have a **single origin of replication**, and the lagging strand is synthesized by **DNA polymerase** after an RNA primer is laid down by **RNA primase**. *DNA replication proceeds in one direction* - This statement is **false** because **DNA replication** is a **bidirectional process**, meaning it proceeds in both directions from the origin of replication. - Replication forks move away from the **origin** on both sides, unraveling the DNA and synthesizing new strands. *Bacteria have multiple origins of replication* - This statement is **false**. Most **bacteria** (prokaryotes) have a **single origin of replication** (oriC) on their circular chromosome. - In contrast, **eukaryotes** have **multiple origins of replication** on their linear chromosomes to replicate their much larger genomes efficiently. - While rare exceptions exist in some bacterial species, the general rule for bacterial DNA replication is a single origin. *Lagging strand is synthesized by RNA primase* - This statement is **false**. The **lagging strand** is primarily synthesized by **DNA polymerase III** (in prokaryotes) or **DNA polymerase δ** (in eukaryotes). - **RNA primase** is responsible for synthesizing short **RNA primers** that provide a starting point for DNA polymerase, but it does not synthesize the entire lagging strand itself.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free