RNA Processing and Splicing — MCQs
Apolipoprotein B-48 is made by which process?
Which type of RNA is characterized by the presence of a 7-methylguanosine cap at its 5' end?
What is attached to the 3' end of mRNA after transcription?
Prader-Willi syndrome and Angelman syndrome are examples of what genetic phenomenon?
During eukaryotic protein synthesis, phosphorylation of which of the following is enhanced by insulin?
DNA Methylation is not related to?
Which of the following is a primarily RNA based technique?
What is the primary function of the sigma subunit of prokaryotic RNA polymerase?
What is considered the most critical component of the activated sludge process?
The outer covering of diatoms is made of?
RNA Processing and Splicing Indian Medical PG Practice Questions and MCQs
Question 1: Apolipoprotein B-48 is made by which process?
- A. DNA editing
- B. RNA editing (Correct Answer)
- C. RNA alternate splicing
- D. RNA interference
Explanation: ***RNA editing*** - Apolipoprotein B-48 is synthesized from ApoB-100 mRNA through a process called **RNA editing** (specifically ApoB mRNA editing) - This involves a **cytidine deaminase enzyme (APOBEC-1)** that converts cytidine to uridine at position 6666, changing a glutamine codon (CAA) to a premature stop codon (UAA) in the small intestine - This results in a truncated protein that is 48% the length of ApoB-100 - ApoB-48 is produced in the **intestine**, while ApoB-100 (unedited) is produced in the **liver** *DNA editing* - DNA editing refers to permanent modifications in the DNA sequence itself - The ApoB gene remains unchanged; only the mRNA transcript is edited in intestinal cells - This is not the mechanism for producing ApoB-48 *RNA alternate splicing* - Alternative splicing involves selecting different combinations of exons from pre-mRNA to produce multiple mRNA isoforms - This process creates different protein variants through exon inclusion/exclusion - ApoB-48 production does not involve alternative splicing but rather direct nucleotide modification (C to U) within the coding sequence *RNA interference* - RNA interference (RNAi) is a biological process involving small RNA molecules (siRNA, miRNA) that silence gene expression - RNAi typically degrades mRNA or blocks translation - This process is not involved in generating a truncated protein like ApoB-48 from the same mRNA transcript
Question 2: Which type of RNA is characterized by the presence of a 7-methylguanosine cap at its 5' end?
- A. mRNA (Correct Answer)
- B. snRNA (small nuclear RNA)
- C. tRNA (transfer RNA)
- D. rRNA (ribosomal RNA)
Explanation: ***mRNA*** - The **7-methylguanosine cap** at the 5' end of mRNA is crucial for **ribosome binding** during translation initiation in eukaryotes. - This cap also protects the mRNA from degradation by **exonucleases**, thus increasing its stability and half-life in the cytoplasm. *tRNA (transfer RNA)* - tRNA molecules are characterized by a conserved **cloverleaf secondary structure** and an **acceptor stem** for amino acid attachment, not a 7-methylguanosine cap. - Their primary function is to **carry specific amino acids** to the ribosome during protein synthesis. *rRNA (ribosomal RNA)* - rRNA molecules are the main structural and catalytic components of **ribosomes**, where protein synthesis occurs. - They do not possess a 7-methylguanosine cap; instead, they undergo extensive **post-transcriptional modifications** and folding to form functional ribosomal subunits. *snRNA (small nuclear RNA)* - **snRNA** molecules are key components of the **spliceosome**, which catalyzes the removal of introns from pre-mRNA. - Unlike mRNA, snRNA molecules have a **trimethylguanosine cap** (not 7-methylguanosine) and are primarily localized in the nucleus for RNA splicing functions.
Question 3: What is attached to the 3' end of mRNA after transcription?
- A. CCA
- B. Intron
- C. 7-methylguanosine
- D. Poly-A tail (Correct Answer)
Explanation: ***Poly-A tail*** - A **poly-A tail**, consisting of multiple adenosine monophosphates, is added to the **3' end of mRNA** after transcription to protect it from degradation. - This modification aids in the **transport of mRNA from the nucleus to the cytoplasm** and in its translation. *CCA* - The **CCA sequence** is found at the **3' end of tRNA**, not mRNA, and is critical for amino acid attachment. - It is added post-transcriptionally to tRNA molecules by the enzyme **tRNA nucleotidyltransferase**. *Intron* - **Introns** are non-coding regions within a gene that are transcribed into mRNA but are subsequently removed during **RNA splicing**, not added to the 3' end. - Their removal ensures that only the **coding regions (exons)** are translated into protein. *7-methylguanosine* - **7-methylguanosine** forms the **5' cap** of mRNA, which is added to the 5' end, not the 3' end. - This cap is important for **mRNA stability**, ribosome binding, and protection against degradation.
Question 4: Prader-Willi syndrome and Angelman syndrome are examples of what genetic phenomenon?
- A. Gene Knockout
- B. Impaired DNA repair
- C. Genomic Imprinting (Correct Answer)
- D. RNA interference
Explanation: ***Genomic Imprinting*** - **Genomic imprinting** is an epigenetic phenomenon where certain genes are expressed in a **parent-of-origin-specific manner**. - In Prader-Willi syndrome, the disease results from the loss of function of specific genes on chromosome 15 (15q11-q13) inherited from the father, while Angelman syndrome results from the loss of function of a different gene (UBE3A) in the same region, but inherited from the mother. *RNA interference* - **RNA interference** is a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules. - This process is not directly responsible for the parent-of-origin-specific expression patterns observed in these syndromes. *Gene Knockout* - A **gene knockout** is a genetic technique in which an organism's genes are made inoperative. - While it involves modifying gene function, it does not explain the differential expression based on parental origin. *Impaired DNA repair* - **Impaired DNA repair** refers to defects in the mechanisms that correct DNA damage. - This can lead to increased mutations and conditions like cancer, but it is not the underlying mechanism for Prader-Willi or Angelman syndromes.
Question 5: During eukaryotic protein synthesis, phosphorylation of which of the following is enhanced by insulin?
- A. eIF2
- B. eIF4A
- C. eIF4G
- D. eIF4E (Correct Answer)
Explanation: ***eIF4E*** - Insulin activates the **mTOR pathway**, which leads to activation of **Mnk1/2 kinases** that phosphorylate eIF4E at **Ser209**. - This phosphorylation enhances eIF4E's **affinity for the 5' cap structure** and increases **cap-dependent translation initiation** efficiency. *eIF4G* - While eIF4G is essential for **eIF4F complex formation**, its phosphorylation is not the primary target enhanced by insulin signaling. - Insulin's effect on eIF4G is mainly **indirect through 4E-BP1 phosphorylation**, which releases eIF4E to bind eIF4G. *eIF2* - **eIF2 phosphorylation** by kinases like **PERK, PKR, and GCN2** inhibits translation initiation during stress conditions. - This is **opposite to insulin's anabolic effects**, as insulin signaling typically promotes conditions that reduce eIF2 phosphorylation. *eIF4A* - eIF4A functions as an **RNA helicase** in the eIF4F complex, unwinding mRNA secondary structures. - While important for translation, **direct phosphorylation enhancement by insulin** is not a primary mechanism for eIF4A regulation.
Question 6: DNA Methylation is not related to?
- A. DNA Replication
- B. Gene silencing
- C. Capping (Correct Answer)
- D. Mismatch repair
Explanation: ***Capping*** - **Capping** is a modification of messenger RNA (mRNA) that occurs during **mRNA processing** in eukaryotes, involving the addition of a 7-methylguanosine cap to the 5' end of the mRNA molecule. - This process is crucial for mRNA stability, translation initiation, and nuclear export, and is entirely **independent of DNA modifications** like DNA methylation. *DNA Replication* - DNA methylation plays a role in **DNA replication** to distinguish newly synthesized strands from parental strands during **DNA repair**. - In bacteria, methylation at specific sites (**Dam methylase**) helps in **mismatch repair** by identifying the parental strand. *Gene silencing* - **DNA methylation** of CpG islands in promoter regions is a well-established mechanism for **gene silencing** by altering chromatin structure and preventing transcription factor binding. - This epigenetic modification leads to stable transcriptional repression and is critical for processes like X-chromosome inactivation and genomic imprinting. *Mismatch repair* - In prokaryotes, **DNA methylation** marks the parental strand, which is used by the **mismatch repair system** to correct errors on the newly synthesized, unmethylated strand. - In eukaryotes, while not directly marking strands, DNA methylation can influence the efficiency of mismatch repair pathways by altering chromatin accessibility.
Question 7: Which of the following is a primarily RNA based technique?
- A. Next generation sequencing
- B. RT-PCR (Correct Answer)
- C. Sanger's technique
- D. Western blotting
Explanation: ***RT-PCR (Reverse Transcriptase PCR)*** - RT-PCR is a **primarily RNA-based technique** that uses **RNA as the initial template** - The enzyme **reverse transcriptase** converts RNA into complementary DNA (cDNA) in the first step - This technique is essential for studying **gene expression**, detecting **RNA viruses**, and analyzing **mRNA levels** - Unlike standard PCR which amplifies DNA, RT-PCR **begins with RNA** as the starting material *Next generation sequencing* - NGS is primarily used for **sequencing DNA fragments** - While RNA-seq exists, it requires **conversion of RNA to cDNA** first, and the actual sequencing chemistry reads DNA - The core technology is **DNA-based** *Sanger's technique* - **Sanger sequencing** is a method for determining the **nucleotide sequence of DNA** - It directly uses **DNA as a template** and does not involve RNA - This is a classical **DNA sequencing method** *Western blotting* - This technique is used for the **detection and quantification of specific proteins** - It involves protein separation by electrophoresis, membrane transfer, and antibody detection - This is a **protein-based technique**, not nucleic acid-based
Question 8: What is the primary function of the sigma subunit of prokaryotic RNA polymerase?
- A. Is inhibited by α-amanitin
- B. Specifically recognizes the promoter site (Correct Answer)
- C. Is part of the core enzyme
- D. Inhibits the activity of RNA polymerase
Explanation: ***Specifically recognizes the promoter site*** - The **sigma subunit** is crucial for **transcription initiation** in prokaryotes, enabling the RNA polymerase holoenzyme to specifically bind to **promoter sequences** on the DNA. - This specific recognition ensures that transcription begins at the correct start site, making it a key component for accurate gene expression. *Inhibits the activity of RNA polymerase* - The sigma subunit does not inhibit RNA polymerase; rather, it **facilitates** its activity by guiding it to the correct transcription start sites. - After initiation, the sigma subunit often **dissociates** from the core enzyme, allowing the core polymerase to proceed with elongation. *Is inhibited by α-amanitin* - **α-amanitin** is a toxin that primarily inhibits **eukaryotic RNA polymerases**, particularly RNA polymerase II, and is not known to inhibit prokaryotic RNA polymerase or its sigma subunit. - Prokaryotic RNA polymerase has a different structure and mechanism, rendering it **insensitive** to α-amanitin. *Is part of the core enzyme* - The sigma subunit is **not considered part of the core enzyme**; the core enzyme consists of the α, β, β', and ω subunits. - Together with the core enzyme, the sigma subunit forms the **RNA polymerase holoenzyme**, which is responsible for initiating transcription.
Question 9: What is considered the most critical component of the activated sludge process?
- A. Primary sedimentation tank
- B. Sludge digester
- C. Aeration tank (Correct Answer)
- D. Final settling tank
Explanation: ***Aeration tank*** - The **aeration tank** is where **microorganisms** are mixed with wastewater, supplied with oxygen, and allowed to break down organic pollutants. This biological process is central to the activated sludge method. - Without proper aeration and microbial activity in this tank, the **biological treatment** and pollutant removal would not occur effectively. *Primary sedimentation tank* - The **primary sedimentation tank** is involved in **pre-treatment**, removing settleable solids from raw wastewater before it enters the biological treatment. - While important for reducing the load on the activated sludge process, it does not perform the core **biological degradation** that defines the process. *Sludge digester* - The **sludge digester** processes the excess sludge generated from the activated sludge system to reduce its volume and stabilize it, often producing **biogas**. - It is a **post-treatment** component for sludge management, not directly involved in the primary biological treatment of wastewater. *Final settling tank* - The **final settling tank**, also known as a clarifier, separates the treated water from the **activated sludge microorganisms** after the aeration tank. - Its role is to clarify the effluent and return the active sludge to the aeration tank, making it crucial for solids separation but not for the actual **biological purification** itself.
Question 10: The outer covering of diatoms is made of?
- A. Magnesium
- B. Silica (Correct Answer)
- C. Hydrocarbons
- D. None of the options
Explanation: ***Correct: Silica*** - The cell walls of diatoms are primarily composed of **hydrated amorphous silica (SiO2·nH2O)**. - This rigid, intricate outer covering is known as a **frustule**, which provides structural support and protection. - Diatoms are uniquely characterized by their intricate silica cell walls, making them easily identifiable under microscopy. *Incorrect: Magnesium* - **Magnesium (Mg)** is an important metal and a component of chlorophyll, essential for photosynthesis. - While diatoms do contain magnesium for metabolic processes, it is not the primary structural component of their outer covering. *Incorrect: Hydrocarbons* - **Hydrocarbons** are organic compounds consisting entirely of hydrogen and carbon, commonly found in fossil fuels. - Diatom cell walls are inorganic (mineral-based), not organic hydrocarbon structures. *Incorrect: None of the options* - This option is incorrect because **silica** is listed among the options and is the correct answer. - Diatom frustules are definitively composed of silica.
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