Rucete ✏ AP Biology In a Nutshell
14. Transcription and Translation — Practice Questions 3
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 structure is directly responsible for recognizing the start codon on an mRNA strand during translation?
(A) rRNA in the ribosome
(B) RNA polymerase
(C) DNA polymerase
(D) Release factor
Answer
(A) — Ribosomal RNA (rRNA) within the ribosome recognizes the start codon and aligns the mRNA for translation.
2. If a stop codon mutates into a sense codon, which of the following is most likely to occur?
(A) Translation will terminate early
(B) The ribosome will produce a longer-than-normal protein
(C) Transcription will not initiate
(D) RNA splicing will fail
Answer
(B) — A sense codon will be read as coding for an amino acid, so translation continues past its normal stop point.
3. What is the role of the poly-A tail during the life of an mRNA molecule in the cytoplasm?
(A) Initiates transcription
(B) Signals the ribosome to bind
(C) Extends mRNA stability for translation
(D) Promotes exon skipping
Answer
(C) — The poly-A tail helps protect the mRNA from degradation and allows more rounds of translation.
4. A retrovirus has integrated its genetic material into a host genome. Which enzyme was critical for this process?
(A) RNA polymerase II
(B) DNA polymerase I
(C) Reverse transcriptase
(D) Ligase
Answer
(C) — Reverse transcriptase converts viral RNA into DNA, which is then integrated into the host genome.
5. What sequence feature allows eukaryotic cells to produce multiple distinct proteins from a single gene?
(A) Ribosomal redundancy
(B) RNA polymerase variants
(C) Alternative splicing of exons
(D) GTP capping of mRNA
Answer
(C) — Alternative splicing allows exons to be combined in different ways, producing various proteins from the same gene.
6. Which process converts a DNA sequence into an RNA message?
(A) Replication
(B) Transcription
(C) Translation
(D) Splicing
Answer
(B) — Transcription is the synthesis of RNA from a DNA template.
7. What molecule serves as the template for translation?
(A) DNA
(B) mRNA
(C) tRNA
(D) rRNA
Answer
(B) — Messenger RNA (mRNA) contains the codon sequence used during translation to assemble proteins.
8. Which of the following modifications is unique to eukaryotic pre-mRNA?
(A) Shine-Dalgarno sequence
(B) 5′ capping with methyl-GTP
(C) Codon recognition
(D) RNA polymerase binding
Answer
(B) — Eukaryotic pre-mRNA receives a 5′ GTP cap to protect it and aid in ribosome binding.
9. What is the role of the E site in a ribosome during translation?
(A) Entry point for mRNA
(B) Exit site for tRNA
(C) Enzyme activation region
(D) Elongation of polypeptides
Answer
(B) — The E (exit) site is where tRNAs exit the ribosome after donating their amino acid.
10. Which of the following best describes a codon?
(A) Three-nucleotide sequence in DNA
(B) Three-nucleotide sequence in RNA that codes for an amino acid
(C) Enzyme that splices mRNA
(D) Part of the ribosomal RNA
Answer
(B) — A codon is a set of three RNA nucleotides that correspond to a specific amino acid.
11. What amino acid does the codon AUG code for?
(A) Alanine
(B) Methionine
(C) Serine
(D) Tyrosine
Answer
(B) — AUG codes for methionine and also serves as the universal start codon.
12. Which process requires RNA polymerase to bind to a promoter region?
(A) Translation
(B) RNA splicing
(C) Transcription
(D) DNA replication
Answer
(C) — RNA polymerase binds to a promoter to begin transcribing DNA into RNA.
13. What is the function of the anticodon on a tRNA molecule?
(A) It binds to the DNA template
(B) It links amino acids together
(C) It pairs with the codon on mRNA
(D) It signals the ribosome to start
Answer
(C) — The anticodon base-pairs with the complementary codon on mRNA to ensure accurate translation.
14. Which organelle is the site of protein synthesis?
(A) Golgi apparatus
(B) Nucleus
(C) Ribosome
(D) Lysosome
Answer
(C) — Ribosomes are the cellular structures where translation occurs and proteins are synthesized.
15. What distinguishes prokaryotic transcription from eukaryotic transcription?
(A) RNA uses thymine instead of uracil
(B) Eukaryotes require transcription factors for initiation
(C) Prokaryotes splice introns
(D) Eukaryotic mRNA is translated in the nucleus
Answer
(B) — Eukaryotic RNA polymerase needs general transcription factors to initiate transcription at promoters.
16. What term describes the flow of information from gene to protein?
(A) RNA cycle
(B) Genetic loop
(C) Central dogma
(D) Replicon theory
Answer
(C) — The central dogma describes the flow of genetic information from DNA to RNA to protein.
17. Which mRNA modification helps ribosomes recognize and bind to the transcript in eukaryotes?
(A) Exon skipping
(B) Poly-A tail
(C) 5′ methyl cap
(D) Introns
Answer
(C) — The 5′ cap is essential for ribosome recognition during translation initiation.
18. What happens to mRNA after the stop codon is reached during translation?
(A) The ribosome starts over from the beginning
(B) The ribosome pauses but continues
(C) A release factor binds, and the ribosome disassembles
(D) The mRNA is digested by exonuclease
Answer
(C) — Release factors recognize stop codons and trigger release of the completed polypeptide and disassembly of the ribosome.
19. Which of the following occurs in eukaryotic cells but not prokaryotic cells?
(A) Codon recognition
(B) Peptide bond formation
(C) RNA polymerase activity
(D) RNA splicing
Answer
(D) — Eukaryotic cells remove introns through RNA splicing; prokaryotic mRNAs do not contain introns.
20. What determines the order of amino acids in a protein?
(A) The anticodon sequence
(B) The DNA replication site
(C) The sequence of codons in mRNA
(D) The ribosomal RNA structure
Answer
(C) — Codons in mRNA dictate which amino acids are added during translation.
21. What is the function of aminoacyl-tRNA synthetase?
(A) Catalyzes peptide bond formation
(B) Removes introns from pre-mRNA
(C) Attaches amino acids to tRNA
(D) Adds a GTP cap to mRNA
Answer
(C) — This enzyme charges tRNA with the correct amino acid before translation.
22. Which base pair is correct in RNA but not in DNA?
(A) A–T
(B) A–U
(C) G–T
(D) C–A
Answer
(B) — In RNA, adenine pairs with uracil (A–U), whereas in DNA, adenine pairs with thymine (A–T).
23. Which structure protects mRNA from degradation in the cytoplasm?
(A) Ribosome
(B) Introns
(C) Poly-A tail
(D) Codon wheel
Answer
(C) — The poly-A tail at the 3′ end helps stabilize and protect eukaryotic mRNA from enzymatic degradation.
24. Which direction does RNA polymerase move along the DNA template strand?
(A) 5′ to 3′ direction
(B) 3′ to 5′ direction
(C) Random orientation
(D) Both simultaneously
Answer
(B) — RNA polymerase reads the DNA template in the 3′ to 5′ direction to synthesize RNA 5′ to 3′.
25. What determines where RNA polymerase begins transcription in eukaryotes?
(A) The ribosome binding site
(B) A specific tRNA
(C) Promoter sequence like the TATA box
(D) Start codon AUG
Answer
(C) — Promoters such as the TATA box provide the binding site for transcription initiation by RNA polymerase II.
26. A eukaryotic cell is exposed to a drug that inhibits the addition of the 5′ cap to mRNA. What is the most immediate consequence?
(A) Transcription will be blocked
(B) mRNA will be spliced incorrectly
(C) The mRNA will degrade quickly and not be translated
(D) Amino acids cannot attach to tRNA
Answer
(C) — Without a 5′ cap, mRNA is unstable in the cytoplasm and cannot be efficiently translated.
27. Which situation is most likely to result from a mutation in the gene encoding aminoacyl-tRNA synthetase?
(A) Ribosome fails to recognize stop codons
(B) tRNA is not charged with the correct amino acid
(C) RNA polymerase cannot transcribe genes
(D) mRNA is exported too slowly
Answer
(B) — This enzyme is responsible for attaching the correct amino acid to each tRNA; mutation can cause mistranslation.
28. A researcher deletes the terminator sequence in a bacterial gene. What is the most likely effect?
(A) Transcription will stop prematurely
(B) Transcription will continue beyond the intended gene
(C) Translation will stop early
(D) The ribosome will disassemble before initiation
Answer
(B) — Without a terminator, RNA polymerase may continue transcribing past the gene’s end.
29. Why do eukaryotic mRNAs have introns while prokaryotic mRNAs generally do not?
(A) Prokaryotes don’t express proteins
(B) Eukaryotes require longer ribosomes
(C) Eukaryotic genes are more modular and regulated
(D) Prokaryotes transcribe RNA in the nucleus
Answer
(C) — Introns allow more flexible regulation and variation in gene expression (e.g., alternative splicing).
30. Which of the following correctly matches an enzyme with its function in gene expression?
(A) Ligase – removes introns
(B) RNA polymerase – synthesizes mRNA
(C) Peptidyl transferase – adds poly-A tail
(D) tRNA synthetase – reads DNA codons
Answer
(B) — RNA polymerase reads DNA and synthesizes complementary RNA molecules.
31. In prokaryotes, what would be the effect of a mutation in the Shine-Dalgarno sequence of an mRNA?
(A) Transcription will stop
(B) mRNA will not be exported from the nucleus
(C) Ribosomes will not recognize the mRNA for translation
(D) The poly-A tail will not form
Answer
(C) — Shine-Dalgarno sequences help prokaryotic ribosomes bind mRNA; mutation would prevent translation initiation.
32. A mutation causes a ribosome to skip the A site during elongation. Which outcome is most likely?
(A) Translation proceeds faster
(B) A frameshift mutation is corrected
(C) No amino acids will be added
(D) Transcription will compensate
Answer
(C) — The A site accepts new tRNA-amino acid complexes; without it, translation cannot proceed.
33. A DNA sequence is transcribed into mRNA, but the resulting protein is nonfunctional due to a missing domain. What is a likely explanation?
(A) RNA polymerase failed to bind the promoter
(B) The gene lacked a start codon
(C) Alternative splicing excluded an essential exon
(D) The poly-A tail was too long
Answer
(C) — Incorrect splicing can result in missing protein domains, even if translation proceeds normally.
34. Which of the following best explains why multiple ribosomes can translate a single mRNA simultaneously?
(A) Codons do not overlap
(B) The ribosome is very small
(C) The mRNA loops back on itself
(D) Ribosomes can attach at multiple points along mRNA
Answer
(D) — Polyribosomes (polysomes) allow multiple ribosomes to translate one mRNA molecule at once.
35. What characteristic of the genetic code ensures that some mutations do not alter the final protein product?
(A) Directionality
(B) Universality
(C) Degeneracy
(D) Polarity
Answer
(C) — Degeneracy (redundancy) means that multiple codons code for the same amino acid, which can lead to silent mutations.
36. Explain why transcription and translation are said to be coupled in prokaryotic cells.
Answer
Prokaryotes lack a nucleus, so ribosomes can begin translating mRNA while it is still being transcribed by RNA polymerase.
37. Describe the role of the 3′ poly-A tail in eukaryotic mRNA.
Answer
The poly-A tail protects mRNA from enzymatic degradation, assists in nuclear export, and helps initiate translation.
38. What would be the result if a mutation caused a tRNA to carry the wrong amino acid?
Answer
The wrong amino acid would be incorporated into the growing polypeptide, possibly leading to a malfunctioning or nonfunctional protein.
39. How does the structure of tRNA allow it to function in translation?
Answer
tRNA has an anticodon loop to pair with mRNA codons and an acceptor stem to bind a specific amino acid, allowing accurate translation.
40. Describe one way that alternative splicing increases protein diversity in eukaryotic cells.
Answer
By rearranging which exons are included or excluded, a single gene can produce multiple mRNA transcripts, leading to different protein isoforms.
41. What would happen if a stop codon in an mRNA were mutated into a sense codon?
Answer
Translation would continue beyond the normal endpoint, resulting in an abnormally long and likely nonfunctional protein.
42. Explain how RNA polymerase knows where to start transcription.
Answer
RNA polymerase recognizes and binds to promoter sequences upstream of the gene, such as the TATA box in eukaryotes.
43. What is the function of a release factor during translation?
Answer
A release factor binds to the stop codon in the A site of the ribosome, causing the polypeptide chain to be released and the ribosome to disassemble.
44. Why does uracil appear in RNA but not in DNA?
Answer
Uracil replaces thymine in RNA because it's energetically cheaper to produce and sufficient for RNA’s typically short lifespan.
45. Describe what happens during the elongation phase of translation.
Answer
tRNAs deliver amino acids to the ribosome, peptide bonds form between them, and the ribosome moves along the mRNA to read the next codon.
46. How does the structure of mRNA ensure the correct reading frame during translation?
Answer
The presence of a start codon (AUG) defines the correct reading frame, and codons are read in groups of three nucleotides from that point.
47. What would be the result of a deletion mutation that shifts the mRNA reading frame?
Answer
A frameshift mutation would alter all downstream codons, producing a completely different and likely nonfunctional protein.
48. How does the wobble hypothesis contribute to efficiency in translation?
Answer
The wobble hypothesis states that the third base of a codon can tolerate mismatches, allowing fewer tRNAs to recognize more codons.
49. What is one key difference between transcription in prokaryotes and eukaryotes?
Answer
In prokaryotes, transcription and translation occur simultaneously in the cytoplasm; in eukaryotes, transcription occurs in the nucleus followed by processing and export.
50. Explain how base-pairing rules apply during transcription.
Answer
RNA polymerase matches complementary RNA bases to the DNA template: A pairs with U, T with A, C with G, and G with C.