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📝 Translation RNA to protein (12 MCQs)

📖 From Principles of Biochemistry • 1. The Foundations of Biochemistry • 12 questions available

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What is Translation RNA to protein?

Definition:
Translation is the process by which the genetic information encoded in mRNA is decoded by ribosomes to synthesize a polypeptide chain, where codons on the mRNA are recognized by transfer RNA (tRNA) molecules carrying specific amino acids, and the sequence of codons determines the amino acid sequence of the protein, following the genetic code, and this process is essential for protein synthesis and cellular function.

Working:
Translation works by ribosomes assembling at the start codon (AUG) on mRNA, and tRNAs bring amino acids to the ribosome, where anticodons pair with codons; the ribosome catalyzes the formation of peptide bonds between amino acids, extending the polypeptide chain until a stop codon is reached, releasing the protein; the process requires energy (GTP) and is divided into initiation, elongation, and termination, and the accuracy is high due to proofreading mechanisms; the rate of translation is about 10-20 amino acids per second in bacteria, and it is regulated by various factors.

Example:
A simple example is the synthesis of hemoglobin in red blood cell precursors, where the mRNA for the globin chain is translated into a polypeptide that folds into the functional protein, and the sequence of amino acids is determined by the codons in the mRNA, illustrating how genetic information is expressed as a functional protein.

Reason:
Translation is fundamental to life because proteins carry out most cellular functions, and understanding this process is crucial for genetics, medicine, and biotechnology, as it explains how genes are expressed, how mutations affect protein function, and how antibiotics target bacterial translation.

Easy

Medium

Hard

📝 All Translation RNA to protein MCQs

Q1. A researcher changes one codon in an mRNA from $5'-AUG-3'$ to $5'-AUA-3'$ . The altered mRNA is translated in a system where initiation normally begins at the first suitable start codon. What is the most likely immediate consequence?

A.Translation begins normally and inserts methionine

B.The ribosome may fail to initiate at that position because the usual start signal is lost ✅

C.A stop codon is automatically created after every amino acid

D.The ribosome changes the reading frame at every downstream codon

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The codon $AUG$ commonly serves as the translation initiation signal and specifies methionine. Changing it to $AUA$ removes that signal, so initiation at that position can be impaired rather than simply replacing one amino acid in an already initiated chain.

Q2. A ribosome reads the mRNA sequence $5'-AUG-GCU-UUU-UGA-3'$ . If the reading frame is preserved from the first codon, which peptide is produced before termination?

A.Methionine–alanine–phenylalanine ✅

B.Alanine–phenylalanine–methionine

C.Methionine–glycine–phenylalanine

D.Methionine–alanine–leucine

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Translation proceeds in consecutive three-nucleotide codons beginning with the initiation codon. $AUG$ specifies methionine, $GCU$ specifies alanine, and $UUU$ specifies phenylalanine; $UGA$ signals termination, so the peptide contains three amino acids.

Q3. Why can two mRNAs containing different nucleotide sequences sometimes produce proteins with the same amino-acid sequence?

A.Every nucleotide directly specifies a unique amino acid

B.Some amino acids are represented by multiple codons, allowing synonymous codon changes ✅

C.Ribosomes translate nucleotides in pairs rather than triplets

D.Transfer RNAs randomly select amino acids during translation

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The genetic code is degenerate, meaning multiple codons can specify the same amino acid. Therefore, a nucleotide substitution may alter an mRNA codon without changing the amino acid incorporated, potentially preserving the protein sequence.

Q4. A mutation changes an mRNA codon from $5'-GAA-3'$ to $5'-GAG-3'$ . A student predicts that the protein must change because the nucleotide sequence changed. Which evaluation is most accurate?

A.The prediction is necessarily correct because every nucleotide change changes a protein

B.The prediction is incorrect because the two codons can specify the same amino acid ✅

C.The prediction is correct because ribosomes cannot recognize altered codons

D.The prediction is incorrect because mRNA is never read during translation

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The two codons $GAA$ and $GAG$ can both specify glutamate. Thus, although the nucleotide sequence changes, the encoded amino acid can remain unchanged. This illustrates how sequence variation does not always produce a protein-level change.

Q5. A cell produces a normal protein when an mRNA contains $5'-AUG-AAA-GGC-CCU-UAA-3'$ . A mutation inserts one nucleotide immediately after $AAA$ . Which outcome is most likely?

A.Only the amino acid encoded by

AAA

changes

B.All downstream codons may be regrouped, potentially altering many downstream amino acids and termination ✅

C.Translation becomes completely independent of the mRNA sequence

D.Only the final stop signal changes while all amino acids remain identical

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Insertion of a single nucleotide changes the grouping of downstream nucleotides into codons. Because translation depends on consecutive triplets, the reading frame can shift, potentially changing many amino acids and causing premature or delayed termination.

Q6. A drug causes ribosomes to pause whenever they encounter a particular codon. In cells treated with the drug, proteins containing that codon are synthesized more slowly. Which interpretation best explains the observation?

A.The codon has disappeared from the mRNA

B.Ribosomal movement or decoding at that codon has become rate-limiting ✅

C.DNA replication has stopped immediately

D.The protein sequence must automatically become shorter

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Protein synthesis depends on repeated cycles of codon recognition, amino-acid delivery, and peptide-bond formation. If ribosomes pause at one codon, that step becomes slower, reducing the rate of elongation without necessarily changing the encoded protein sequence.

Q7. An mRNA has the sequence $5'-AUG-GCU-UUU-UAA-3'$ . A mutation changes the third codon from $UUU$ to $UUA$ . If translation remains in the same reading frame, what is the most reasonable prediction?

A.The protein necessarily gains an additional amino acid

B.The protein can contain a different amino acid at that position because the codon meaning changes ✅

C.Translation must start at

UUA

instead of

AUG

D.The mutation removes the entire mRNA molecule

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Changing $UUU$ to $UUA$ changes the codon being interpreted by the ribosome. Because these codons can specify different amino acids, the resulting polypeptide may contain a substitution at that position while the reading frame remains intact.

Q8. A student claims, 'Because ribosomes read mRNA from $3'$ to $5'$ , reversing an mRNA sequence should produce the same protein if the same nucleotides are present.' What is the key error?

A.The ribosome does not use nucleotides at all

B.Translation depends on directional reading of codons, so reversing the sequence changes codon order and usually the encoded peptide ✅

C.Proteins are assembled directly from DNA without RNA

D.Only stop codons determine the amino-acid sequence

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Ribosomes decode mRNA directionally, and codons are interpreted in an ordered reading frame. Reversing the nucleotide sequence generally changes both codon composition and order, so the resulting peptide will usually differ substantially.

Q9. A graph shows protein-production rate on the $y$ -axis and ribosome concentration on the $x$ -axis. The curve rises steeply at low ribosome concentration but approaches a plateau at high concentration. Which conclusion best explains the graph?

A.Adding ribosomes always increases protein production proportionally without limit

B.At high ribosome concentration, another factor becomes limiting, so additional ribosomes produce progressively smaller increases ✅

C.Ribosomes destroy mRNA at high concentration

D.Protein production is independent of ribosome concentration

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: The initial increase suggests ribosome availability limits translation when ribosomes are scarce. The plateau indicates that another component, such as mRNA, charged tRNAs, initiation capacity, or cellular resources, becomes limiting as ribosome concentration increases.

Q10. Two mRNAs encode proteins of equal length. mRNA X contains many codons that are frequently used in the cell, whereas mRNA Y contains mostly rare codons. If ribosome availability and amino-acid supply are otherwise comparable, what is the most reasonable prediction?

A.mRNA Y must always produce a longer protein

B.mRNA X may be translated more efficiently because its codons can be decoded more readily in that cellular context ✅

C.mRNA X cannot be translated because common codons inhibit ribosomes

D.Both must translate at exactly the same rate regardless of codon usage

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Codon usage can influence translation efficiency because different codons may correspond to different abundances of compatible tRNAs. Frequently used codons can sometimes support faster decoding, although the exact effect depends on cellular conditions and context.

Q11. A mutation creates a premature stop codon halfway through an mRNA coding region. The ribosome begins normally but terminates at the new stop signal. Which combined consequence is most likely?

A.A longer protein containing every original amino acid is produced

B.A shorter polypeptide is produced, potentially lacking structural regions needed for normal function ✅

C.The DNA sequence is immediately converted into protein

D.Translation continues through the stop codon without any effect

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: A premature stop codon causes translation to terminate earlier than intended. The resulting polypeptide is shorter and may lack domains or structural elements required for proper folding, interactions, localization, or biological activity.

Q12. A synthetic mRNA contains $5'-AUG-AAA-GCU-UGG-UAG-3'$ . Suppose a mutation changes $UGG$ to $UAG$ . Which reasoning correctly predicts the effect?

A.One amino acid is substituted, but translation continues normally

B.A stop signal is introduced where an amino-acid codon previously existed, causing earlier termination ✅

C.The start codon moves three positions downstream

D.The reading frame shifts because a nucleotide was inserted

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: $UGG$ normally specifies an amino acid, whereas $UAG$ is a termination signal. Replacing $UGG$ with $UAG$ therefore converts an amino-acid-encoding position into a stop signal, shortening the resulting polypeptide.

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