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Biochemistry and Molecular Biology

Transcription and Translation Practice Questions

22 free Transcription and Translation practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 22 Medium

Which enzyme is primarily responsible for synthesizing pre-mRNA from DNA in eukaryotic cells?

  1. A RNA polymerase I
  2. B RNA polymerase II
  3. C RNA polymerase III
  4. D DNA polymerase II

Correct answer: RNA polymerase II

In eukaryotes, RNA polymerase II transcribes protein-coding genes into pre-mRNA. RNA polymerase I and III transcribe rRNA and tRNA/rRNA components respectively.

Question 2 of 22 Medium

Which of the following correctly describes the order of major stages of transcription?

  1. A Termination → Initiation → Elongation
  2. B Initiation → Elongation → Termination
  3. C Elongation → Termination → Initiation
  4. D Initiation → Termination → Elongation

Correct answer: Initiation → Elongation → Termination

Transcription proceeds through initiation (binding of polymerase to promoter), elongation (RNA strand synthesis), then termination (release of transcript).

Question 3 of 22 Medium

During eukaryotic mRNA processing, what modification is added to the 5′ end of the nascent transcript soon after initiation?

  1. A 3' poly-adenosine tail addition
  2. B 7-methylguanosine cap
  3. C Free 5' triphosphate group
  4. D 3' polyuridine tract segment

Correct answer: 7-methylguanosine cap

Eukaryotic pre-mRNA is capped at its 5′ end with a 7-methylguanosine cap shortly after transcription begins. This protects the mRNA and helps in its processing and transport.

Question 4 of 22 Medium

In prokaryotes, what feature of their mRNA allows expression of multiple proteins from a single transcript?

  1. A Polyadenylation
  2. B Alternative splicing
  3. C Polycistronic mRNA
  4. D 5′ capping

Correct answer: Polycistronic mRNA

Prokaryotic mRNAs are often polycistronic — a single mRNA carries coding sequences for multiple genes, enabling synthesis of several proteins from one transcript.

Question 5 of 22 Medium

What is the role of aminoacyl-tRNA synthetase in translation?

  1. A It catalyzes peptide-bond formation between amino acids on the ribosome
  2. B It attaches the correct amino acid to its cognate tRNA, consuming ATP
  3. C It unwinds mRNA secondary structure prior to small-subunit ribosome binding
  4. D It excises non-coding introns from eukaryotic pre-mRNA before export

Correct answer: It attaches the correct amino acid to its cognate tRNA, consuming ATP

Aminoacyl-tRNA synthetases catalyze the esterification of a specific amino acid to its corresponding tRNA using ATP, producing charged tRNA for translation.

Question 6 of 22 Medium

During translation in bacteria, which of the following factors brings the initiator tRNA to the ribosome P-site and hydrolyzes GTP to allow subunit joining?

  1. A IF1
  2. B IF2
  3. C IF3
  4. D EF-G

Correct answer: IF2

In bacterial translation initiation, initiation factor IF2 (a GTP-binding protein) escorts the initiator tRNA to the P-site; GTP hydrolysis triggers joining of the large ribosomal subunit and start of elongation. This is a key difference in initiation mechanisms of translation.

Question 7 of 22 Medium

Which of the following statements is TRUE about eukaryotic pre-mRNA but FALSE for prokaryotic mRNA?

  1. A It can be immediately translated upon synthesis
  2. B It contains introns and undergoes splicing
  3. C It is polycistronic
  4. D It is synthesized by a holoenzyme with sigma factor

Correct answer: It contains introns and undergoes splicing

Eukaryotic pre-mRNA includes introns which are removed via splicing; prokaryotic mRNA generally lacks introns and does not undergo splicing.

Question 8 of 22 Medium

Which RNA polymerase transcribes tRNA and 5S rRNA in eukaryotic cells?

  1. A Eukaryotic RNA polymerase I
  2. B Eukaryotic RNA polymerase II
  3. C Eukaryotic RNA polymerase III
  4. D Eukaryotic RNA polymerase IV

Correct answer: Eukaryotic RNA polymerase III

In eukaryotes, RNA polymerase III transcribes tRNAs, 5S rRNA, and some small nuclear RNAs important for splicing, while RNA polymerase II transcribes pre-mRNAs.

Question 9 of 22 Medium

Why does the third base of a codon often allow “wobble” pairing, reducing the need for a unique tRNA for every codon?

  1. A Because the third codon base is always a guanine or cytosine residue
  2. B Because the tRNA anticodon tolerates non-Watson-Crick pairing there
  3. C Because the ribosome simply ignores the third base of every codon
  4. D Because there are far more sense codons than there are amino acids

Correct answer: Because the tRNA anticodon tolerates non-Watson-Crick pairing there

The third base of a codon often allows wobble between codon and anticodon, meaning a single tRNA can recognize multiple codons that differ only at the third nucleotide — reducing the number of distinct tRNAs required.

Question 10 of 22 Medium

Which of these processes occur before export of a newly transcribed mRNA from the nucleus in eukaryotes?

  1. A Cytoplasmic translation initiation on the mRNA
  2. B 5' capping, intron splicing, and polyadenylation
  3. C tRNA charging by aminoacyl synthetases
  4. D Assembly of the 80S ribosomal subunits

Correct answer: 5' capping, intron splicing, and polyadenylation

Before export to the cytoplasm, eukaryotic pre-mRNA undergoes 5′ capping, intron splicing, and 3′ poly-A tail addition to become mature mRNA. Only mature mRNA can be exported and translated.

Question 11 of 22 Medium

Which statement best explains why translation can begin on a bacterial mRNA even while it is still being transcribed?

  1. A Bacteria splice introns during translation
  2. B Bacterial mRNA is polyadenylated before translation
  3. C Transcription and translation both occur in the cytoplasm and can be coupled
  4. D Bacteria have no ribosomes, so translation waits until transcription completes

Correct answer: Transcription and translation both occur in the cytoplasm and can be coupled

In prokaryotes, transcription and translation both occur in the cytoplasm, with no nuclear compartment. Thus ribosomes can begin translating mRNA even before transcription is finished, allowing coupling of both processes.

Question 12 of 22 Medium

During eukaryotic transcription initiation, which component directly binds the TATA box in the promoter region to help recruit RNA polymerase II?

  1. A TFIID (TATA-binding protein)
  2. B Sigma factor
  3. C EF-Tu
  4. D Spliceosome

Correct answer: TFIID (TATA-binding protein)

In eukaryotic transcription initiation, the general transcription factor TFIID — containing TATA-binding protein (TBP) — binds the TATA box and helps recruit RNA polymerase II to form the pre-initiation complex.

Question 13 of 22 Medium

What energy source is directly used by aminoacyl-tRNA synthetase during tRNA charging?

  1. A GTP
  2. B ATP
  3. C CTP
  4. D No energy required — spontaneous

Correct answer: ATP

Aminoacyl-tRNA synthetases use ATP hydrolysis to form a high-energy ester bond between the tRNA 3′ end and its specific amino acid. This “charging” is energy-dependent.

Question 14 of 22 Medium

Which of the following is NOT a common feature of eukaryotic mRNA but present in bacterial mRNA?

  1. A 5' 7-methylguanosine cap structure
  2. B 3' poly-adenosine (poly-A) tail
  3. C Polycistronic coding sequences
  4. D Introns (intervening sequences)

Correct answer: Polycistronic coding sequences

Polycistronic transcripts (multiple proteins from one mRNA) are typical of bacterial mRNA; most eukaryotic mRNAs are monocistronic. So polycistronic coding is not a feature of eukaryotic mRNA.

Question 15 of 22 Medium

Which type of RNA is produced by RNA polymerase I in eukaryotic cells?

  1. A mRNA (messenger transcripts)
  2. B tRNA (transfer transcripts)
  3. C Large-subunit ribosomal rRNA
  4. D snRNA (spliceosomal RNAs)

Correct answer: Large-subunit ribosomal rRNA

RNA polymerase I transcribes rRNA precursors (except 5S rRNA), including large-subunit rRNAs, in the nucleolus — supplying components for ribosome assembly.

Question 16 of 22 Medium

During translation termination, what causes the release of the completed polypeptide from the ribosome?

  1. A Encounter of a stop codon and binding of release factors
  2. B Depletion of charged tRNAs available in the cytoplasm
  3. C Endonucleolytic degradation of the mRNA being read
  4. D Hydrolysis of GTP bound to elongation factor EF-G

Correct answer: Encounter of a stop codon and binding of release factors

When a ribosome reaches a stop codon, no corresponding tRNA exists. Instead, release factors bind and promote hydrolysis of the bond between the polypeptide and tRNA, freeing the completed protein.

Question 17 of 22 Medium

Which of the following best describes the template strand during transcription?

  1. A The DNA strand whose sequence matches the mRNA, apart from T being U
  2. B The DNA strand read as the base-pairing template by RNA polymerase
  3. C The non-coding strand that is never transcribed during gene expression
  4. D The strand complementary to the mRNA that stays fully double-stranded

Correct answer: The DNA strand read as the base-pairing template by RNA polymerase

The template (antisense) strand is the one read by RNA polymerase in 3′→5′ direction to build a complementary RNA in 5′→3′ direction. The non-template (coding) strand has the same sequence as mRNA (with T→U).

Question 18 of 22 Medium

Why are introns spliced out of eukaryotic pre-mRNA before translation?

  1. A Introns are non-coding and would disrupt the reading frame if left in
  2. B Introns themselves encode functional signal peptides
  3. C Introns markedly reduce the stability of the mRNA
  4. D Introns are strictly required for the 5' capping step

Correct answer: Introns are non-coding and would disrupt the reading frame if left in

Introns are non-coding intervening sequences that interrupt the open reading frame; they must be removed by splicing so the mature mRNA carries a continuous, correctly framed coding sequence for translation.

Question 19 of 22 Medium

Which of the following is true about the genetic code used in translation?

  1. A It is overlapping, with each nucleotide shared between several adjacent codons
  2. B It is ambiguous, with a single codon coding for several different amino acids
  3. C It is non-overlapping and universal, each codon specifying one amino acid
  4. D It uses DNA codons read from the template strand to specify amino acids directly

Correct answer: It is non-overlapping and universal, each codon specifying one amino acid

The genetic code is nearly universal, non-overlapping, and unambiguous: each three-nucleotide mRNA codon specifies a single amino acid (or a stop signal). It is not overlapping, not ambiguous, and reads mRNA codons rather than DNA directly.

Question 20 of 22 Medium

Which process is responsible for stabilizing mature eukaryotic mRNA and aiding its export from the nucleus?

  1. A The 5′ cap is added and then quickly removed before export
  2. B Splicing of introns acting as the sole stabilizing step
  3. C Addition of the 5′ cap together with the 3′ poly-A tail
  4. D Charging of tRNAs with amino acids for use in translation

Correct answer: Addition of the 5′ cap together with the 3′ poly-A tail

Both the 5′ cap and the 3′ poly-A tail protect mature mRNA from degradation and promote its export from the nucleus to the cytoplasm. Splicing and tRNA charging do not perform this role, and the cap is retained, not removed.

Question 21 of 22 Medium

Which of the following accurately reflects a difference between eukaryotic and prokaryotic gene expression?

  1. A Eukaryotes often produce polycistronic mRNA, prokaryotes produce monocistronic
  2. B Prokaryotic mRNA is capped and polyadenylated, eukaryotic mRNA is not
  3. C In eukaryotes, transcription occurs in nucleus; in prokaryotes, in cytoplasm
  4. D Translation precedes transcription in prokaryotes

Correct answer: In eukaryotes, transcription occurs in nucleus; in prokaryotes, in cytoplasm

Eukaryotic transcription occurs in the nucleus whereas prokaryotes lack a nucleus so transcription and translation occur in the cytoplasm.

Question 22 of 22 Medium

What happens to the σ factor of bacterial RNA polymerase after initial transcription initiation?

  1. A It stays bound to the core polymerase throughout the elongation phase
  2. B It dissociates after about 10 nucleotides have been synthesized
  3. C It is rapidly degraded by cellular proteases
  4. D It is converted into a transcription termination factor

Correct answer: It dissociates after about 10 nucleotides have been synthesized

After initiation and synthesis of the first ~10 nucleotides, the σ factor dissociates from the bacterial core RNA polymerase, which then continues elongation on its own. The σ factor is recycled, not degraded, and does not become a termination factor.

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