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📝 Gene expression (DNA → mRNA → protein) (7 MCQs)

📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 7 questions available

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What is Gene expression (DNA → mRNA → protein)?

Definition:
Gene expression is the process through which information stored in DNA is used to produce a functional product, often a protein. In a typical pathway, DNA information is transcribed into messenger RNA $mRNA$ , which is then translated into a protein.

Working:
During transcription, a DNA sequence is copied into $mRNA$ . During translation, ribosomes read the $mRNA$ sequence and assemble amino acids in the specified order.

Example:
If an $mRNA$ contains the codon $AUG$ , it signals the beginning of translation and corresponds to the amino acid methionine.

Reason:
Gene expression connects stored genetic information with observable cellular functions because proteins and functional RNAs perform many essential biological activities.

Easy

Medium

Hard

📝 All Gene expression (DNA → mRNA → protein) MCQs

Q1. A researcher observes that a gene contains the information for a protein, but the protein is produced in the cytoplasm rather than directly from DNA. Which sequence best explains how the information is transferred?

A.DNA → protein → mRNA

B.DNA → mRNA → protein ✅

C.mRNA → DNA → protein

D.Protein → DNA → mRNA

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: DNA stores the hereditary information, but its sequence is not normally translated directly into protein. Instead, transcription produces an mRNA copy of the gene, and ribosomes then use the mRNA sequence to determine the amino acid sequence of the protein.

Q2. Two cells contain identical DNA but produce very different proteins. Which conclusion best explains this observation?

A.Their DNA must have completely different nucleotide sequences

B.Only the cell producing more proteins contains functional genes

C.Different genes can be selectively expressed in different cell types ✅

D.Protein production occurs independently of DNA sequence

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: Cells with the same genome can have different characteristics because different sets of genes are expressed. Regulation of transcription and subsequent steps allows particular cells to produce specific mRNAs and proteins while other genes remain inactive.

Q3. A mutation changes one DNA nucleotide in a gene, but the resulting protein is unchanged. Which explanation is most plausible?

A.DNA mutations can never affect gene expression

B.The altered nucleotide may produce an mRNA codon that still specifies the same amino acid ✅

C.mRNA is produced without using DNA information

D.Proteins always correct nucleotide mutations before translation

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: A nucleotide substitution can change an mRNA codon without changing the encoded amino acid because multiple codons can specify the same amino acid. Therefore, a DNA change does not necessarily alter the final protein sequence.

Q4. A scientist blocks transcription of a particular gene while leaving translation machinery fully functional. Shortly afterward, production of the corresponding protein decreases. What is the best explanation?

A.Translation immediately changes DNA into protein

B.Blocking transcription prevents formation of new mRNA templates needed for translation ✅

C.Ribosomes permanently stop functioning when transcription is blocked

D.The protein is converted back into DNA when transcription stops

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Transcription is required to generate mRNA from the DNA template. When transcription is blocked, existing mRNA molecules may continue to support translation temporarily, but as they degrade, fewer templates remain and production of the corresponding protein decreases.

Q5. A student claims: “If a gene is present in a cell's DNA, the corresponding protein must always be produced.” Which observation most directly identifies the flaw in this reasoning?

A.Every cell contains DNA

B.Some genes are transcribed only under particular cellular conditions ✅

C.Proteins contain amino acids

D.DNA contains nucleotides

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: The presence of a gene does not guarantee that it is actively expressed. Cells regulate gene expression according to their type, developmental stage, environmental signals, and physiological requirements, so many genes can remain transcriptionally inactive.

Q6. The graph below represents protein production after transcription of a gene is suddenly stopped. Protein concentration remains nearly constant for a short period, then gradually decreases. Which interpretation best fits the pattern? Time: 0, 10, 20, 30, 40 min; Protein: 100, 99, 92, 72, 45 units.

A.Protein must be synthesized directly from DNA continuously

B.Existing mRNA and proteins can persist temporarily even after new transcription stops ✅

C.Stopping transcription immediately destroys all proteins

D.Translation necessarily increases when transcription stops

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Existing mRNA molecules can continue to be translated after transcription is stopped, so protein production does not necessarily cease immediately. As mRNA and protein molecules are degraded or diluted, the measured protein concentration can subsequently decline.

Q7. Two genes are transcribed at similar rates, but Gene X produces much more protein than Gene Y. Further analysis shows that Gene X has more stable mRNA and its mRNA is translated more efficiently. What best explains the difference?

A.DNA sequence cannot influence protein production

B.Protein abundance depends only on transcription rate

C.Gene X benefits from regulation at both mRNA stability and translation ✅

D.Gene Y must lack DNA

💡 Difficulty: hard | ✅ Correct: C

📖 Explanation: Gene expression is a multistep process rather than a simple transcription-to-protein switch. Even when transcription rates are similar, differences in mRNA stability and translation efficiency can substantially change how much protein accumulates.

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