Genetic code MCQs With Answer

Understanding the genetic code is essential for B. Pharm students preparing for pharmacogenomics, drug design, and molecular biology applications. This Genetic code MCQs With Answer set covers core concepts—codons, anticodons, start and stop signals, degeneracy, wobble pairing, and code variations in mitochondria—that affect protein synthesis and therapeutic strategies. Questions emphasize practical insights such as codon usage bias, translational recoding (selenocysteine/pyrrolysine), frameshift consequences, and implications for recombinant protein expression and mutation effects. Clear, concise explanations and answer keys help reinforce learning and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which nucleotide triplet in mRNA specifies the start of translation in most prokaryotes?

• AUG
• UGA
• UAA
• UAG

Correct Answer: AUG

Q2. Which codon is recognized as a stop codon in the standard genetic code?

• AUG
• UAA
• GCU
• UUU

Correct Answer: UAA

Q3. What is meant by ‘degeneracy’ of the genetic code?

• Each amino acid is encoded by only one codon
• Multiple codons can specify the same amino acid
• Codons can change during translation
• Codons do not have a defined reading frame

Correct Answer: Multiple codons can specify the same amino acid

Q4. Which phenomenon explains tolerance of mismatches at the third base of the codon?

• Frameshift mutation
• Wobble hypothesis
• Transversion
• Recombination

Correct Answer: Wobble hypothesis

Q5. Which amino acid is encoded by the codons UUU and UUC?

• Leucine
• Phenylalanine
• Tyrosine
• Serine

Correct Answer: Phenylalanine

Q6. In eukaryotes, which sequence around the start codon enhances translation initiation?

• Shine-Dalgarno sequence
• Kozak sequence
• TATA box
• Poly-A tail

Correct Answer: Kozak sequence

Q7. Which tRNA feature pairs with an mRNA codon during translation?

• 3′ CCA tail
• Anticodon loop
• Acceptor stem
• D arm

Correct Answer: Anticodon loop

Q8. Which codon universally encodes methionine and often serves as the initiation codon?

• UUG
• AUG
• GUG
• CUA

Correct Answer: AUG

Q9. What effect does a nonsense mutation have on the encoded protein?

• Substitutes one amino acid for another
• Introduces a premature stop codon
• Shifts the reading frame downstream
• Does not change the amino acid sequence

Correct Answer: Introduces a premature stop codon

Q10. Which of the following is an example of a synonymous mutation?

• UGG to UGA causing stop
• GAA to GAG both encoding glutamic acid
• AAA to AAG causing lysine to arginine
• CUA to CUA causing leucine to isoleucine

Correct Answer: GAA to GAG both encoding glutamic acid

Q11. The ‘wobble’ base is typically at which position of the codon?

• First (5′ end)
• Second (middle)
• Third (3′ end)
• It varies randomly

Correct Answer: Third (3′ end)

Q12. Which amino acid is uniquely encoded by a single codon (UGG) in the standard code?

• Tryptophan
• Methionine
• Tryptamine
• Proline

Correct Answer: Tryptophan

Q13. What is a frameshift mutation?

• A point mutation substituting one base
• Insertion or deletion altering the reading frame
• A mutation that changes codon degeneracy
• A mutation only in tRNA genes

Correct Answer: Insertion or deletion altering the reading frame

Q14. Which codon can be redefined to insert selenocysteine under specific contexts?

• UAG
• UGA
• UAA
• AAA

Correct Answer: UGA

Q15. Codon usage bias refers to:

• Random distribution of codons in genomes
• Preference for certain synonymous codons in a species
• Equal usage of all codons across organisms
• Bias only seen in mitochondrial DNA

Correct Answer: Preference for certain synonymous codons in a species

Q16. Which feature differentiates initiator tRNA (tRNAfMet) in bacteria?

• It carries valine
• It is formylated at the amino group
• It lacks an anticodon
• It binds stop codons

Correct Answer: It is formylated at the amino group

Q17. Which organelle uses a variant genetic code in many organisms?

• Nucleus
• Mitochondrion
• Ribosome
• Endoplasmic reticulum

Correct Answer: Mitochondrion

Q18. How many possible codons exist in a triplet nucleotide code (4^3)?

• 16
• 64
• 20
• 32

Correct Answer: 64

Q19. Which codon commonly serves as a start codon in prokaryotes besides AUG?

• GUG
• UAA
• AGA
• CCC

Correct Answer: GUG

Q20. A missense mutation results in:

• Insertion of a stop codon
• No change in amino acid
• Change in one amino acid to another
• Loss of entire gene

Correct Answer: Change in one amino acid to another

Q21. Which enzyme charges tRNA with its cognate amino acid?

• Ribulose bisphosphate carboxylase
• Aminoacyl-tRNA synthetase
• DNA polymerase
• Peptidyl transferase

Correct Answer: Aminoacyl-tRNA synthetase

Q22. The open reading frame (ORF) is defined as:

• A DNA segment lacking introns
• A continuous stretch of codons from start to stop without interruption
• A protein binding site
• A promoter region

Correct Answer: A continuous stretch of codons from start to stop without interruption

Q23. Which codon is reassigned to tryptophan in human mitochondria instead of a stop?

• UGA
• UAG
• UAA
• AAA

Correct Answer: UGA

Q24. Synonymous codons differ at which nucleotide position most often?

• First
• Second
• Third
• They never differ

Correct Answer: Third

Q25. Which statement about the genetic code is correct?

• It is completely universal with no exceptions
• It is nearly universal but has known variations
• It varies randomly within individuals
• It only applies to eukaryotes

Correct Answer: It is nearly universal but has known variations

Q26. Which sequence in prokaryotic mRNA helps ribosome binding and position of start codon?

• Kozak sequence
• Shine-Dalgarno sequence
• TATA box
• Polyadenylation signal

Correct Answer: Shine-Dalgarno sequence

Q27. What is ‘recoding’ in translation?

• Regular translation with no modifications
• Programmed changes in decoding, e.g., selenocysteine insertion
• DNA methylation events
• Transcription termination

Correct Answer: Programmed changes in decoding, e.g., selenocysteine insertion

Q28. Which codon codes for proline?

• CCU
• AUG
• GAA
• UUU

Correct Answer: CCU

Q29. What is the impact of codon optimization in recombinant protein production?

• Decreases expression always
• Can improve expression by matching host codon bias
• Eliminates amino acid sequence
• Converts prokaryotic genes to eukaryotic genes

Correct Answer: Can improve expression by matching host codon bias

Q30. Which of the following is NOT a stop codon?

• UAG
• UGA
• AUG
• UAA

Correct Answer: AUG

Q31. Which mechanism allows one mRNA to produce different proteins via frame selection?

• Alternative splicing only
• Alternative reading frames (overlapping genes)
• DNA replication
• Transcriptional attenuation

Correct Answer: Alternative reading frames (overlapping genes)

Q32. Pyrrolysine is incorporated at which codon in certain archaea and bacteria?

• UAG
• UAA
• UGG
• UAC

Correct Answer: UAG

Q33. Which base substitution is a transition?

• A to C
• A to G
• A to T
• C to T (same type)

Correct Answer: A to G

Q34. Which codon pair signals termination in translation?

• Start–Stop pair
• Stop codons such as UAA, UAG, UGA
• Initiator anticodon pairs
• Poly-A signal

Correct Answer: Stop codons such as UAA, UAG, UGA

Q35. How does a silent mutation affect the protein?

• Alters amino acid sequence
• Introduces a stop codon
• No change in amino acid due to codon redundancy
• Always causes disease

Correct Answer: No change in amino acid due to codon redundancy

Q36. What role does the anticodon play in translation fidelity?

• It catalyzes peptide bond formation
• Pairs with mRNA codon to ensure correct amino acid incorporation
• Transcribes DNA to mRNA
• Determines ribosome assembly only

Correct Answer: Pairs with mRNA codon to ensure correct amino acid incorporation

Q37. Which concept explains why different organisms prefer different synonymous codons?

• Genetic drift only
• Codon usage bias influenced by tRNA abundance and selection
• Universal codon frequencies
• Random mutation without selection

Correct Answer: Codon usage bias influenced by tRNA abundance and selection

Q38. In which reading frame does translation start in a correct ORF?

• Any frame randomly
• Frame with start codon in proper context
• Frame that maximizes stop codons
• Frame determined by introns

Correct Answer: Frame with start codon in proper context

Q39. Which mutation type can cause a gain of stop codon leading to truncated protein?

• Missense
• Nonsense
• Silent
• Conservative

Correct Answer: Nonsense

Q40. Which amino acid is encoded by codons starting with ‘AU’ (AUU, AUC, AUA)?

• Isoleucine
• Alanine
• Asparagine
• Leucine

Correct Answer: Isoleucine

Q41. Which is true about the standard genetic code table?

• It maps 64 codons to 20 amino acids and stop signals
• It maps 20 codons to 64 amino acids
• It has no redundancy
• It changes within the same organism frequently

Correct Answer: It maps 64 codons to 20 amino acids and stop signals

Q42. Which experimental approach is used to determine codon assignments historically?

• X-ray crystallography of DNA only
• In vitro translation with synthetic RNAs
• Southern blotting
• Whole-genome sequencing

Correct Answer: In vitro translation with synthetic RNAs

Q43. Which codon pair is recognized by release factors to terminate translation in bacteria?

• Start codons
• Stop codons (UAA, UAG, UGA)
• Any codon followed by AUG
• Anticodon loops

Correct Answer: Stop codons (UAA, UAG, UGA)

Q44. A single nucleotide insertion near the start codon most likely causes:

• Silent mutation
• Frameshift affecting downstream protein sequence
• Increased transcription only
• No effect due to wobble

Correct Answer: Frameshift affecting downstream protein sequence

Q45. Which amino acid codons include a CGN pattern (CGU, CGC, CGA, CGG)?

• Arginine
• Glycine
• Glutamine
• Serine

Correct Answer: Arginine

Q46. Why is knowledge of the genetic code important for B. Pharm students?

• Only relevant for clinicians, not pharmacists
• It underpins pharmacogenomics, drug targets, and recombinant protein therapeutics
• It replaces knowledge of pharmacokinetics
• It is obsolete

Correct Answer: It underpins pharmacogenomics, drug targets, and recombinant protein therapeutics

Q47. What determines which codon is translated more efficiently in a host organism?

• tRNA abundance and codon usage bias
• Only the GC content of DNA
• The number of introns
• Protein tertiary structure

Correct Answer: tRNA abundance and codon usage bias

Q48. What is the consequence of a truncation mutation caused by early stop codon?

• Longer protein with added domains
• Shortened protein that may lose function or gain harmful function
• No change in function
• Always beneficial to the cell

Correct Answer: Shortened protein that may lose function or gain harmful function

Q49. Which method would you use to change codon usage to improve human expression of a bacterial gene?

• Codon optimization—alter synonymous codons to match human bias
• Introduce random frameshifts
• Replace start codon with stop codon
• Avoid altering any codons

Correct Answer: Codon optimization—alter synonymous codons to match human bias

Q50. In which scenario can UGA code for an amino acid rather than a stop codon?

• Never; UGA is always stop
• During selenocysteine incorporation with SECIS element and specialized factors
• Only in prokaryotic ribosomes always
• Only when Kozak sequence is absent

Correct Answer: During selenocysteine incorporation with SECIS element and specialized factors

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com