301. Which statement best describes hnRNA in eukaryotic cells?
ⓐ. It is the primary transcript that contains both exons and introns.
ⓑ. It is the fully processed mRNA ready for translation immediately after transcription.
ⓒ. It is the ribosomal RNA of the large subunit.
ⓓ. It is the amino-acid carrier during protein synthesis.
Correct Answer: It is the primary transcript that contains both exons and introns.
Explanation: Heterogeneous nuclear RNA, or hnRNA, is the initial transcript produced from many eukaryotic protein-coding genes. At this stage it still contains both exons and introns and is not yet ready for translation. Additional processing is needed before it becomes mature mRNA. This is one of the key differences between eukaryotic and many prokaryotic transcripts.
302. Which process removes introns from hnRNA and joins the exons together?
ⓐ. capping
ⓑ. tailing
ⓒ. aminoacylation
ⓓ. splicing
Correct Answer: splicing
Explanation: Splicing is the process by which introns are removed from the primary transcript and exons are joined into a continuous sequence. This step converts interrupted information into a usable RNA message. Without splicing, the transcript would still contain non-coding segments. It is therefore an essential stage of eukaryotic RNA processing.
303. Which modification occurs at the 5' end of hnRNA during processing?
ⓐ. addition of a poly-A tail
ⓑ. removal of exons
ⓒ. addition of methyl guanosine triphosphate cap
ⓓ. addition of amino acids
Correct Answer: addition of methyl guanosine triphosphate cap
Explanation: The 5' end of hnRNA is modified by the addition of a cap containing methyl guanosine triphosphate. This capping is an early processing event in eukaryotic mRNA formation. It helps stabilize the RNA and supports later steps in gene expression. The 3' end, in contrast, receives the poly-A tail.
304. Which statement correctly describes tailing of hnRNA?
ⓐ. About 200–300 adenylate residues are added at the 3' end.
ⓑ. A phosphate cap is added at the 3' end.
ⓒ. Introns are added back after splicing.
ⓓ. Ribose is replaced by deoxyribose at the 3' end.
Correct Answer: About 200–300 adenylate residues are added at the 3' end.
Explanation: Tailing refers to the addition of a poly-A tail at the 3' end of the transcript. In this chapter treatment, the tail consists of about 200–300 adenylate residues. This modification is part of the processing that converts hnRNA into mature mRNA. It helps distinguish processed eukaryotic mRNA from the initial primary transcript.
305. Which sequence correctly represents the main processing events that convert hnRNA into mature mRNA?
ⓐ. translation → capping → tailing
ⓑ. tailing → DNA replication → splicing
ⓒ. splicing → protein folding → capping
ⓓ. capping, tailing, and splicing
Correct Answer: capping, tailing, and splicing
Explanation: Eukaryotic hnRNA must undergo several processing steps before it becomes mature mRNA. These include 5' capping, 3' tailing, and removal of introns by splicing. Together, these modifications produce a stable and functional transcript that can be exported to the cytoplasm. The mature mRNA is therefore a processed product, not the raw primary transcript.
306. Which statement best distinguishes mature eukaryotic mRNA from the initial hnRNA transcript?
ⓐ. Mature mRNA is processed by capping, tailing, and splicing, whereas hnRNA is the unprocessed primary transcript.
ⓑ. Mature mRNA contains introns only, whereas hnRNA contains exons only.
ⓒ. Mature mRNA is made directly by ribosomes, whereas hnRNA is made by DNA polymerase.
ⓓ. Mature mRNA remains permanently inside the nucleus, whereas hnRNA is translated in the cytoplasm.
Correct Answer: Mature mRNA is processed by capping, tailing, and splicing, whereas hnRNA is the unprocessed primary transcript.
Explanation: Eukaryotic hnRNA is the primary transcript produced during transcription and still contains both exons and introns. Before it can function as mRNA, it undergoes several processing steps. These include capping at the 5' end, tailing at the 3' end, and splicing to remove introns. The resulting mature mRNA is therefore a modified and functional transcript.
307. Which modification is added specifically to the 3' end of eukaryotic hnRNA during processing?
ⓐ. methyl guanosine cap
ⓑ. poly-A tail
ⓒ. anticodon loop
ⓓ. histone core
Correct Answer: poly-A tail
Explanation: The 3' end of hnRNA receives a long stretch of adenylate residues during processing. This is called the poly-A tail. It is distinct from the 5' cap, which is added at the opposite end of the transcript. The presence of the tail is one of the key features of mature eukaryotic mRNA.
308. What is the most direct result of splicing during eukaryotic RNA processing?
ⓐ. DNA is converted into RNA.
ⓑ. Ribosomes are assembled on the transcript.
ⓒ. Introns are removed and exons are joined together.
ⓓ. Amino acids are attached to the RNA molecule.
Correct Answer: Introns are removed and exons are joined together.
Explanation: Splicing acts on the primary RNA transcript after transcription. Its role is to remove the non-coding introns and connect the coding exons into one continuous sequence. This step is necessary before the transcript can function properly as mature mRNA. It is therefore a processing event, not a translational one.
309. After proper processing, mature mRNA is transported from the nucleus to the
ⓐ. ribosome only in bacteria
ⓑ. cell wall
ⓒ. nucleolus
ⓓ. cytoplasm
Correct Answer: cytoplasm
Explanation: In eukaryotic cells, transcription and RNA processing take place inside the nucleus. Once the transcript has been properly processed into mature mRNA, it is exported to the cytoplasm. There it can associate with ribosomes for translation. This nuclear-to-cytoplasmic movement is a standard step in eukaryotic gene expression.
310. Which statement correctly compares eukaryotic mRNA formation with bacterial mRNA formation?
ⓐ. Eukaryotic hnRNA usually undergoes capping, tailing, and splicing, whereas bacterial mRNA does not typically require this same pattern of processing.
ⓑ. Bacterial mRNA is always spliced extensively, whereas eukaryotic mRNA is produced fully mature at transcription.
ⓒ. Both eukaryotic and bacterial mRNAs are formed only after translation is complete.
ⓓ. Bacterial mRNA is produced by RNA polymerase II, whereas eukaryotic mRNA is produced by a single RNA polymerase.
Correct Answer: Eukaryotic hnRNA usually undergoes capping, tailing, and splicing, whereas bacterial mRNA does not typically require this same pattern of processing.
Explanation: Eukaryotic primary transcripts usually need substantial processing before becoming functional mRNA. This includes 5' capping, 3' tailing, and splicing to remove introns. In bacteria, transcription and translation are often coupled, and the same kind of extensive processing is not the usual pattern. This difference reflects the greater complexity of eukaryotic gene expression.
311. A eukaryotic transcript still contains introns and lacks both 5' capping and 3' tailing. It is best described as
ⓐ. mature mRNA
ⓑ. hnRNA
ⓒ. tRNA
ⓓ. rRNA
Correct Answer: hnRNA
Explanation: A transcript that still contains introns and has not yet received the usual end modifications is still in its primary form. In eukaryotes, this unprocessed precursor is called hnRNA. Only after processing steps are completed does it become mature mRNA. The description therefore fits hnRNA rather than any final RNA product.
312. Which event occurs at the 5' end of a eukaryotic primary transcript?
ⓐ. addition of about 200–300 adenylate residues
ⓑ. removal of promoter sequence
ⓒ. addition of methyl guanosine triphosphate cap
ⓓ. attachment of a specific amino acid
Correct Answer: addition of methyl guanosine triphosphate cap
Explanation: The 5' end of eukaryotic hnRNA is modified by addition of a methyl guanosine triphosphate cap. This is a distinct processing step from 3' tailing, which adds adenylate residues at the other end. The cap is a characteristic feature of mature eukaryotic mRNA. It helps mark the transcript as processed and functional.
313. Which order best represents the sequence from eukaryotic primary transcript to translation-ready mRNA?
ⓐ. mature mRNA → splicing → transcription
ⓑ. exon removal → tailing → DNA replication
ⓒ. translation → capping → RNA export
ⓓ. hnRNA with exons and introns → capping and tailing → splicing → mature mRNA
Correct Answer: hnRNA with exons and introns → capping and tailing → splicing → mature mRNA
Explanation: The primary transcript first exists as hnRNA containing both exons and introns. It then undergoes capping, tailing, and splicing to become mature mRNA. The mature product can then be exported and used in translation. This sequence links RNA processing with gene expression in eukaryotes.
314. Assertion: Mature eukaryotic mRNA differs structurally from the primary transcript synthesized by RNA polymerase II.
Reason: The primary transcript undergoes processing steps before becoming functional mRNA.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains Assertion.
ⓑ. Both Assertion and Reason are true, but Reason does not explain Assertion.
ⓒ. Assertion is true, but Reason is false.
ⓓ. Assertion is false, but Reason is true.
Correct Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.
Explanation: The primary transcript produced by RNA polymerase II is not yet the finished messenger RNA. It must be processed through capping, tailing, and splicing before it becomes mature and functional. This means the mature mRNA is structurally different from the initial transcript. The reason therefore directly explains the assertion.
315. Which statement best explains why processed mRNA, rather than raw hnRNA, is normally used for translation in eukaryotes?
ⓐ. hnRNA contains only rRNA sequences and cannot leave the nucleus.
ⓑ. processed mRNA has undergone the required modifications and removal of introns needed for proper expression.
ⓒ. hnRNA is synthesized by DNA polymerase and therefore is not true RNA.
ⓓ. processed mRNA contains no nucleotide bases and therefore moves faster to ribosomes.
Correct Answer: processed mRNA has undergone the required modifications and removal of introns needed for proper expression.
Explanation: Raw hnRNA still contains intervening sequences and lacks the fully processed form needed for normal gene expression. Through capping, tailing, and splicing, the transcript becomes stable and properly organized as mature mRNA. Only then is it typically exported for translation. Processing therefore prepares the message for correct use in protein synthesis.
316. A eukaryotic primary transcript contains the order 5'-cap region–E1–I1–E2–I2–E3–3' before processing. Which will best represent the mature mRNA?
ⓐ. E1–I1–E2–I2–E3 only
ⓑ. E1–E2–E3 only, without any end modifications
ⓒ. I1–I2–E1–E2–E3 with poly-A tail
ⓓ. 5' cap–E1–E2–E3–poly-A tail
Correct Answer: 5' cap–E1–E2–E3–poly-A tail
Explanation: Mature eukaryotic mRNA is formed after capping, tailing, and splicing. Introns are removed, exons are joined, and the processed transcript retains the 5' cap and the 3' poly-A tail. Therefore the mature message contains E1, E2, and E3 in sequence, flanked by the two end modifications.
317. A mature eukaryotic mRNA lacks its 5' cap but is otherwise correctly spliced and tailed. Which outcome is most directly expected?
ⓐ. It will be transcribed from both DNA strands.
ⓑ. It may not function efficiently in translation.
ⓒ. It will be converted back into DNA.
ⓓ. It will become polycistronic.
Correct Answer: It may not function efficiently in translation.
Explanation: The 5' cap is one of the important processing modifications of eukaryotic mRNA. Even if splicing and tailing are normal, loss of the cap can reduce proper handling and efficient use of the transcript in translation. This shows that RNA processing is not limited to intron removal alone. Multiple modifications contribute to the final usefulness of mRNA.
318. Which statement correctly compares a typical bacterial mRNA with a typical eukaryotic mRNA?
ⓐ. Bacterial mRNA is always capped and tailed, whereas eukaryotic mRNA is not.
ⓑ. Bacterial mRNA is usually monocistronic, whereas eukaryotic mRNA is usually polycistronic.
ⓒ. Bacterial mRNA may be polycistronic and can be translated during transcription, whereas a typical eukaryotic mRNA is usually monocistronic and processed before translation.
ⓓ. Both are always translated only after leaving a membrane-bound nucleus.
Correct Answer: Bacterial mRNA may be polycistronic and can be translated during transcription, whereas a typical eukaryotic mRNA is usually monocistronic and processed before translation.
Explanation: Bacteria often organize related genes in operons, so one mRNA can carry information for multiple polypeptides. Because bacteria lack a nuclear membrane, translation can begin before transcription finishes. In eukaryotes, mRNA is usually monocistronic and must be processed before export and translation. This contrast combines several important chapter-level differences between prokaryotic and eukaryotic expression.
319. Why did the problem of the genetic code become important in molecular biology?
ⓐ. Scientists needed to explain how a nucleotide sequence could specify an amino-acid sequence.
ⓑ. Scientists needed to prove that proteins are made of nucleotides.
ⓒ. Scientists needed to show that DNA replication occurs only in viruses.
ⓓ. Scientists needed to determine why all genes have the same length.
Correct Answer: Scientists needed to explain how a nucleotide sequence could specify an amino-acid sequence.
Explanation: Once it became clear that genes are made of nucleic acids and proteins are built from amino acids, an important question arose. Scientists needed to understand how information written in nucleotides could be translated into a sequence of amino acids. This required discovering the rules by which bases are read during protein synthesis. That set of rules is called the genetic code.
320. Which idea was proposed by George Gamow in relation to the genetic code?
ⓐ. The code is based on one nucleotide for each amino acid.
ⓑ. The code is read only from DNA and never through RNA.
ⓒ. The code is likely to be triplet in nature.
ⓓ. The code is made entirely of stop signals and no sense codons.
Correct Answer: The code is likely to be triplet in nature.
Explanation: George Gamow proposed that the genetic code might use groups of three nucleotides to specify amino acids. This was an important conceptual step because a code based on single or double nucleotides would not provide enough combinations for all amino acids. The triplet idea offered a mathematically reasonable solution. Later experimental work supported this proposal.
