Rucete ✏ AP Biology In a Nutshell
14. Transcription and Translation — Practice Questions
This chapter introduces the flow of genetic information from DNA to RNA to protein, emphasizing the roles of transcription and translation in gene expression.
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(Multiple Choice — Click to Reveal Answer)
1. Which enzyme is responsible for synthesizing RNA from a DNA template?
(A) DNA polymerase
(B) RNA polymerase
(C) Ribosome
(D) Ligase
Answer
(B) — RNA polymerase transcribes the DNA sequence into RNA during transcription.
2. Which of the following modifications is added to the 5′ end of eukaryotic mRNA before it exits the nucleus?
(A) Poly-A tail
(B) Exon
(C) 5′ GTP cap
(D) TATA box
Answer
(C) — The 5′ GTP cap protects the transcript and facilitates ribosome binding.
3. Which structure catalyzes the formation of peptide bonds during translation?
(A) mRNA
(B) tRNA
(C) rRNA
(D) RNA polymerase
Answer
(C) — rRNA acts as a ribozyme within the ribosome to form peptide bonds.
4. Where does transcription occur in a eukaryotic cell?
(A) Cytoplasm
(B) Golgi apparatus
(C) Nucleus
(D) Ribosome
Answer
(C) — In eukaryotes, transcription occurs in the nucleus before mRNA is transported out for translation.
5. A codon is a sequence of how many nucleotides?
(A) 1
(B) 2
(C) 3
(D) 4
Answer
(C) — Codons are triplets of nucleotides that specify amino acids.
6. Which RNA molecule carries amino acids to the ribosome during translation?
(A) mRNA
(B) tRNA
(C) rRNA
(D) snRNA
Answer
(B) — Transfer RNA (tRNA) brings amino acids to the ribosome and matches them with codons in mRNA.
7. Which type of RNA contains codons?
(A) mRNA
(B) tRNA
(C) rRNA
(D) snRNA
Answer
(A) — Messenger RNA (mRNA) contains codons that specify amino acids during translation.
8. Which of the following is the start codon for translation?
(A) UAA
(B) AUG
(C) UGA
(D) UAG
Answer
(B) — AUG is the universal start codon, coding for methionine.
9. What is the function of the poly-A tail in eukaryotic mRNA?
(A) Binds tRNA
(B) Initiates transcription
(C) Stabilizes mRNA and delays degradation
(D) Catalyzes peptide bond formation
Answer
(C) — The poly-A tail protects mRNA from degradation and influences its stability in the cytoplasm.
10. In eukaryotic cells, where does translation occur?
(A) Nucleus
(B) Cytoplasm
(C) Endoplasmic reticulum only
(D) Golgi apparatus
Answer
(B) — Translation occurs in the cytoplasm, either free-floating or on the rough ER.
11. What component of the translation machinery contains the anticodon?
(A) mRNA
(B) Ribosome
(C) tRNA
(D) rRNA
Answer
(C) — Each tRNA molecule contains an anticodon complementary to an mRNA codon.
12. Which of the following is added to the 3′ end of eukaryotic mRNA?
(A) GTP cap
(B) Introns
(C) Spliceosome
(D) Poly-A tail
Answer
(D) — A poly-A tail is added to the 3′ end of the pre-mRNA to enhance stability and translation efficiency.
13. What is the role of RNA polymerase during gene expression?
(A) Adds amino acids to a polypeptide
(B) Removes introns from mRNA
(C) Synthesizes RNA from a DNA template
(D) Translates codons into proteins
Answer
(C) — RNA polymerase synthesizes RNA strands during transcription using DNA as a template.
14. What are exons?
(A) Noncoding regions removed from mRNA
(B) Coding regions retained in mRNA
(C) RNA polymerase subunits
(D) Ribosome binding sites
Answer
(B) — Exons are the coding segments of mRNA that remain after splicing and are translated into protein.
15. Which enzyme is used to transcribe viral RNA into DNA in retroviruses?
(A) RNA polymerase
(B) Reverse transcriptase
(C) Ligase
(D) DNA polymerase I
Answer
(B) — Reverse transcriptase creates a DNA copy of viral RNA in retroviruses.
16. Which of the following occurs during RNA processing in eukaryotes?
(A) DNA replication
(B) Ribosome assembly
(C) Splicing of introns
(D) tRNA synthesis
Answer
(C) — Introns are removed from pre-mRNA to produce mature mRNA for translation.
17. Which of the following does NOT occur in prokaryotic transcription or translation?
(A) Splicing
(B) Translation by ribosomes
(C) Transcription by RNA polymerase
(D) mRNA use of codons
Answer
(A) — Prokaryotic genes do not contain introns, so no splicing occurs.
18. What sequence signals the start of transcription in a gene?
(A) Poly-A tail
(B) Start codon
(C) Promoter region
(D) Stop codon
Answer
(C) — The promoter region (including the TATA box in eukaryotes) is where transcription begins.
19. What is the function of spliceosomes?
(A) Replicate DNA
(B) Remove introns and join exons
(C) Synthesize ribosomes
(D) Cap mRNA with GTP
Answer
(B) — Spliceosomes are complexes that remove introns and splice together coding exons in pre-mRNA.
20. What would be the mRNA complement of the DNA sequence 3′-TAC GGA TCA-5′?
(A) 3′-ATG CCT AGT-5′
(B) 5′-AUG CCU AGU-3′
(C) 5′-UAC GGA UCA-3′
(D) 3′-UAC GGA UCA-5′
Answer
(B) — Transcription replaces T with U and generates a 5′ to 3′ strand: AUG CCU AGU.
21. Which of the following best defines the term "translation"?
(A) Conversion of DNA to RNA
(B) Synthesis of protein from an mRNA template
(C) Removal of introns from RNA
(D) Copying of mRNA into DNA
Answer
(B) — Translation is the synthesis of proteins using information carried by mRNA at the ribosome.
22. Which RNA type helps form the core of the ribosome and catalyze translation?
(A) mRNA
(B) tRNA
(C) rRNA
(D) snRNA
Answer
(C) — Ribosomal RNA (rRNA) is structural and catalytic in forming peptide bonds in the ribosome.
23. Which modification allows nuclear export of mRNA in eukaryotic cells?
(A) Splicing of introns
(B) Poly-A tail
(C) 5′ GTP cap
(D) DNA primer
Answer
(C) — The 5′ cap is required for the transcript to exit the nucleus and initiate translation.
24. Which of the following processes occurs in the cytoplasm of eukaryotic cells?
(A) Transcription
(B) RNA splicing
(C) Translation
(D) 5′ capping
Answer
(C) — Translation takes place in the cytoplasm after mature mRNA exits the nucleus.
25. What feature of the genetic code allows for silent mutations?
(A) Poly-A tail
(B) Wobble base pairing
(C) Multiple stop codons
(D) Redundancy (degeneracy)
Answer
(D) — The redundancy of the genetic code allows different codons to specify the same amino acid.
26. A mutation eliminates the TATA box from the promoter of a eukaryotic gene. What is the most likely result?
(A) The gene will be translated incorrectly.
(B) The gene will be transcribed more efficiently.
(C) RNA polymerase will have difficulty binding, reducing transcription.
(D) Splicing of the pre-mRNA will not occur.
Answer
(C) — The TATA box helps RNA polymerase bind; its deletion reduces transcription initiation.
27. A retrovirus uses reverse transcriptase to insert its genome into a host. What distinguishes this process from typical transcription?
(A) It uses DNA as a template to make RNA.
(B) It uses RNA as a template to make DNA.
(C) It uses ribosomes to replicate its genome.
(D) It uses RNA polymerase to make proteins.
Answer
(B) — Reverse transcriptase copies RNA into DNA, the reverse of typical transcription.
28. Which of the following best explains why prokaryotic translation can begin before transcription is complete?
(A) Prokaryotes have multiple nuclei.
(B) Their ribosomes are inside the nucleus.
(C) Transcription and translation both occur in the cytoplasm.
(D) They use different types of RNA polymerase.
Answer
(C) — Prokaryotes lack a nucleus, so translation begins as mRNA is transcribed.
29. A single eukaryotic gene can lead to several different proteins. What process allows this?
(A) Translation redundancy
(B) Polyadenylation
(C) Alternative splicing
(D) mRNA capping
Answer
(C) — Alternative splicing allows exons to be joined in different ways, producing varied mRNAs.
30. Which of the following most directly causes the high mutation rate in retroviruses?
(A) RNA polymerase lacks proofreading
(B) DNA polymerase has low fidelity
(C) Reverse transcriptase lacks proofreading
(D) Ribosomes make errors in translation
Answer
(C) — Reverse transcriptase is error-prone and lacks proofreading ability, leading to high mutation rates.
31. A researcher deletes a sequence that codes for a poly-A signal. What would most likely happen to the mRNA transcript?
(A) It would be translated twice as fast.
(B) It would never leave the nucleus.
(C) It would degrade quickly in the cytoplasm.
(D) It would be permanently stored in the nucleus.
Answer
(C) — Without a poly-A tail, mRNA is unstable and rapidly degraded in the cytoplasm.
32. Which of the following is a feature shared by both prokaryotic and eukaryotic gene expression?
(A) mRNA splicing
(B) 5′ GTP capping
(C) Transcription using RNA polymerase
(D) Alternative exon usage
Answer
(C) — Both domains use RNA polymerase to transcribe DNA into RNA.
33. Which of the following codons is a stop codon?
(A) AUG
(B) UAA
(C) GUA
(D) CGU
Answer
(B) — UAA is one of three universal stop codons, terminating translation.
34. In translation, what is the role of the ribosome's A site?
(A) Binds the growing polypeptide chain
(B) Releases tRNA after peptide bond formation
(C) Accepts incoming tRNA carrying amino acids
(D) Binds RNA polymerase
Answer
(C) — The A site is where new tRNA with its amino acid enters the ribosome.
35. A scientist observes that a protein's amino acid sequence is unchanged despite a point mutation in the gene. What best explains this observation?
(A) The mutation created a new exon.
(B) The genetic code is redundant.
(C) The mutation activated reverse transcription.
(D) The gene was never transcribed.
Answer
(B) — Due to redundancy in the genetic code, some mutations (silent) do not change the amino acid sequence.
36. Describe how the 5′ GTP cap helps prepare a eukaryotic mRNA for translation.
Answer
The 5′ GTP cap protects the mRNA from degradation, aids in nuclear export, and helps the ribosome recognize the start of translation.
37. Explain why prokaryotes do not need to splice their RNA transcripts.
Answer
Prokaryotic genes do not contain introns, so their RNA transcripts are ready for translation without splicing.
38. Predict what would happen to mRNA stability if the poly-A tail were shortened significantly.
Answer
A shorter poly-A tail would reduce mRNA stability, leading to faster degradation and decreased protein production.
39. Identify the start codon and explain its role in translation.
Answer
The start codon is AUG, which signals the beginning of translation and codes for the amino acid methionine.
40. Describe the function of tRNA in translation.
Answer
tRNA carries specific amino acids to the ribosome and pairs its anticodon with the complementary codon on mRNA to ensure accurate translation.
41. Explain why deletion of an exon from an mRNA transcript can alter the final protein structure.
Answer
Exons contain coding sequences; deleting one can remove essential amino acids and shift the reading frame, leading to a dysfunctional protein.
42. What is a spliceosome and what is its function in eukaryotic cells?
Answer
A spliceosome is a complex of snRNPs and proteins that removes introns from pre-mRNA and joins exons to produce mature mRNA.
43. Justify how alternative splicing increases protein diversity in humans.
Answer
Alternative splicing allows different combinations of exons to be included in mRNA, enabling one gene to produce multiple protein variants.
44. Why can prokaryotic cells perform transcription and translation simultaneously?
Answer
Because prokaryotes lack a nucleus, ribosomes can begin translating mRNA while it is still being transcribed.
45. Define a silent mutation and explain why it often has no effect on protein function.
Answer
A silent mutation changes a codon without altering the amino acid it codes for due to redundancy in the genetic code.
46. Describe the role of ribosomal RNA (rRNA) in the ribosome.
Answer
rRNA forms the core of the ribosome's structure and catalyzes peptide bond formation during translation.
47. Predict the effect of a mutation in the promoter region of a gene.
Answer
The mutation could prevent RNA polymerase from binding properly, reducing or eliminating transcription of the gene.
48. How does redundancy in the genetic code protect organisms from some mutations?
Answer
Multiple codons can code for the same amino acid, so some point mutations do not change the amino acid sequence (silent mutations).
49. What is the role of a release factor during translation?
Answer
A release factor binds to the stop codon on mRNA, triggering the disassembly of the ribosome and release of the newly formed polypeptide.
50. Explain the difference in mRNA processing between prokaryotic and eukaryotic cells.
Answer
Eukaryotic pre-mRNA undergoes splicing, 5′ capping, and poly-A tail addition; prokaryotic mRNA does not require these modifications and can be translated immediately.