D1.2 Protein synthesis
Practice exam-style IB Biology questions for Protein synthesis, aligned with the syllabus and grouped by topic.
Question 1
What is the role of RNA polymerase during transcription?
A.
It joins RNA nucleotides using a DNA strand as a template.
B.
It converts uracil bases in RNA into thymine bases.
C.
It removes introns from a newly synthesized polypeptide.
D.
It joins amino acids in the order specified by mRNA.
Question 2
A DNA template base is adenine. Which base is incorporated into the RNA transcript opposite it?
A.
Adenine
B.
Cytosine
C.
Thymine
D.
Uracil
Question 3
What is translation?
A.
Removal of introns from a primary RNA transcript.
B.
Synthesis of RNA using one strand of DNA as a template.
C.
Replication of DNA before cell division.
D.
Synthesis of a polypeptide using the base sequence of mRNA.
Question 4
A somatic neurone transcribes the same gene many times over decades. What property of the DNA template makes this possible?
A.
The DNA template is degraded after mRNA is produced.
B.
The DNA template is translated directly by ribosomes.
C.
The DNA base sequence is replaced by RNA bases.
D.
The DNA base sequence is conserved after each transcription event.
Question 5
A gene is not transcribed in a cell. What is the most direct consequence for expression of a protein-coding gene?
A.
No mRNA for that gene is available for translation.
B.
All other genes in the cell stop being expressed.
C.
The ribosome changes the DNA sequence to compensate.
D.
The amino acid sequence is copied directly from DNA.
Question 6
An mRNA codon is 5′-GCU-3′. What is the complementary tRNA anticodon?
A.
5′-GCA-3′
B.
3′-GCU-5′
C.
5′-CGA-3′
D.
3′-CGA-5′
Question 7
What is the function of a promoter in transcription?
A.
It is a polypeptide sequence removed after translation.
B.
It is a ribosomal site that holds the next tRNA.
C.
It is an RNA codon that terminates translation.
D.
It is a DNA region where proteins bind to initiate transcription.
Question 8
Which example is a non-coding DNA sequence with a protective structural role?
A.
A tRNA anticodon bound to a ribosome
B.
An mRNA codon for lysine
C.
A telomere at the end of a chromosome
D.
A peptide bond between two amino acids
Question 9
What is the role of proteasomes in maintaining a functional proteome?
A.
They splice exons to make different mature mRNAs.
B.
They pair anticodons with codons during elongation.
C.
They transcribe genes that code for damaged proteins.
D.
They break selected proteins into peptides so amino acids can be recycled.
Question 10
State the molecule used as the template during transcription.
[1]
Outline two roles of RNA polymerase in transcription.
[1]
Question 11
Outline the roles of mRNA, ribosomes and tRNA in translation. [4]
Question 12
What correctly describes the roles of mRNA, ribosomes and tRNA in translation?
A.
mRNA carries codons, tRNA carries amino acids, and the ribosome holds them in position.
B.
mRNA catalyses peptide bonds, tRNA separates DNA strands, and the ribosome makes DNA.
C.
mRNA carries amino acids, tRNA carries codons, and the ribosome stores DNA.
D.
mRNA binds the large ribosomal subunit while DNA binds two tRNAs simultaneously.
Question 13
Why is the genetic code based on triplets of bases rather than pairs of bases?
A.
Triplets prevent all mutations from changing amino acid sequences.
B.
Triplets allow DNA, but not RNA, to contain uracil.
C.
Triplets provide enough possible codons to specify 20 amino acids and stop signals.
D.
Triplets ensure that each amino acid has only one possible codon.
Question 14
What is meant by 5′ to 3′ transcription?
A.
RNA polymerase adds nucleotides to the 3′ end of the growing RNA strand.
B.
RNA polymerase reads the RNA transcript from its 3′ end to its 5′ end.
C.
The DNA coding strand is synthesized from 5′ to 3′ during translation.
D.
Ribosomes add amino acids to the 5′ end of the mRNA molecule.
Question 15
A mature eukaryotic mRNA differs from pre-mRNA because it normally has undergone which process?
A.
Removal of exons, removal of the 5′ end and addition of thymine bases.
B.
Formation of peptide bonds between adjacent codons.
C.
Addition of a 5′ cap, addition of a 3′ polyA tail and splicing of exons.
D.
Attachment of amino acids to anticodons by the ribosome.
Question 16
How can alternative splicing increase protein diversity?
A.
Different ribosomes translate the same codons into unrelated amino acids.
B.
Different combinations of exons from one pre-mRNA produce different mature mRNAs.
C.
Introns are translated into additional amino acids after leaving the nucleus.
D.
The promoter is converted into a polypeptide before splicing occurs.
Question 17
Which change is part of the post-translational modification of insulin?
A.
The insulin promoter is spliced to form an active hormone.
B.
Pre-proinsulin is converted to proinsulin and then to insulin with A and B chains linked by disulfide bonds.
C.
Insulin mRNA is converted directly into glucose by a ribosome.
D.
Proteasomes add a polyA tail to proinsulin in the cytoplasm.
Question 18
A section of a DNA template strand has the sequence 3′-TAC GGA-5′.
Deduce the complementary RNA sequence synthesized from this template.
[1]
Explain how hydrogen bonding contributes to accurate transcription.
[1]
Question 19
Explain why the DNA sequence of a gene must remain stable when it is transcribed repeatedly in a long-lived somatic cell. [3]
Question 20
Two differentiated human cells contain the same gene for an enzyme, but only one cell type produces the enzyme.
State the first stage in expression of this protein-coding gene.
[1]
Explain how the enzyme can be produced in one cell type but not the other.
[1]
Question 21
Distinguish between a codon and an anticodon. [2]
Question 22
Outline initiation of transcription at a promoter. [3]
Question 23
Describe post-transcriptional modification of pre-mRNA in eukaryotic cells. [4]
Question 24
Explain why constant protein breakdown and synthesis are both needed to sustain a functional proteome. [3]
Question 25
A researcher measured RNA production from isolated DNA templates after adding RNA polymerase and ribonucleotides.
Identify the time interval with the greatest increase in RNA produced.
[1]
Describe the overall trend in RNA produced over the experiment.
[1]
Suggest why no RNA was produced in a control without RNA polymerase.
[1]
Question 26
mRNA for three genes was measured in two specialized cell types from the same organism.
Identify the gene most highly expressed in cell type X.
[1]
Compare expression of gene B in the two cell types.
[1]
Evaluate whether the data support the statement that all cells express the same genes at the same rate.
[1]
Question 27
What sequence of events occurs during initiation of translation in eukaryotic cytoplasm?
A.
Proteasomes bind mRNA, fold the polypeptide and attach the initiator tRNA.
B.
RNA polymerase binds the promoter, exons are removed, and the ribosome reads introns.
C.
Large ribosomal subunit binds the 3′ tail, stop codon is located, empty tRNA pairs, small subunit detaches.
D.
Small ribosomal subunit binds the 5′ region, start codon is located, initiator tRNA pairs, large subunit attaches.
Question 28
Explain the significance of degeneracy and universality of the genetic code. [4]
Question 29
Use the genetic code information below:
AUG = methionine, GCU = alanine, UUU = phenylalanine, UGA = stop, CAA = glutamine.
Deduce the amino acid sequence translated from 5′-AUG GCU UUU UGA CAA-3′.
[1]
Explain why CAA is not included in the polypeptide.
[1]
Question 30
Explain directionality in transcription and translation. [3]
Question 31
Distinguish between two examples of non-coding DNA sequences in eukaryotes. [4]
Question 32
Explain how one eukaryotic gene can code for more than one polypeptide variant. [3]
Question 33
Outline how translation initiation sets the reading frame.
[1]
State the roles of the A, P and E sites during elongation.
[1]
Question 34
Explain how translation of insulin mRNA leads to functional insulin. [4]
Question 35
A short mRNA sequence and a genetic code table are provided.
| Information | mRNA codon(s) 5′→3′ | Meaning |
|---|---|---|
| mRNA sequence | GCU UAC AUG CCA GAA UUU UGA CCG | |
| Codon | AUG | Methionine |
| Codon | CCA | Proline |
| Codon | GAA | Glutamic acid |
| Codon | UUU | Phenylalanine |
| Codon | UGA | Stop |
| Codon | GCU | Alanine |
| Codon | UAC | Tyrosine |
| Codon | CCG | Proline |
Identify the first codon translated.
[1]
Deduce the amino acid sequence up to, but not including, the first stop codon.
[1]
Explain why the table must be read using mRNA codons rather than tRNA anticodons.
[1]
Question 36
The movement of one ribosome along an mRNA molecule was tracked during elongation.
State how many codons the ribosome advances in each elongation step.
[1]
Describe the relationship between ribosome position and length of the polypeptide.
[1]
Explain how stepwise movement preserves the amino acid sequence.
[1]
Question 37
A point mutation in a gene changes one codon in the mRNA. The table shows the original and mutated codons and the properties of the amino acids they specify.
| Feature | Original | Mutated |
|---|---|---|
| DNA template triplet (3′→5′) | CTT | CAT |
| mRNA codon (5′→3′) | GAA | GUA |
| Amino acid specified | Glutamic acid (Glu) | Valine (Val) |
| Side-chain property | Negatively charged, polar | Non-polar, hydrophobic |
Identify the type of mutation shown.
[1]
State whether the primary structure of the polypeptide changes.
[1]
Suggest how the amino acid substitution could affect the final protein.
[1]
State one example of a point mutation affecting protein structure.
[1]
Question 38
Cells were transfected with a reporter gene controlled by the same promoter. Different transcription factors were then added.
Identify the condition with the highest reporter mRNA level.
[1]
Compare the effect of transcription factor P and transcription factor Q on transcription.
[1]
Suggest how a transcription factor can alter reporter mRNA production without changing the coding sequence.
[1]
Question 39
The diagram shows exon combinations detected in mature mRNAs from one gene in three tissues.
| Tissue | Variant | E1 | E2 | E3 | E4 | E5 | Introns |
|---|---|---|---|---|---|---|---|
| Liver | L1 | present | present | present | skipped | present | removed |
| Liver | L2 | present | skipped | present | skipped | present | removed |
| Brain | B1 | present | present | present | present | present | removed |
| Brain | B2 | skipped | present | present | present | present | removed |
| Brain | B3 | present | skipped | present | present | skipped | removed |
| Muscle | M1 | skipped | present | present | skipped | present | removed |
| Muscle | M2 | present | skipped | present | present | present | removed |
Identify the exon present in all mature mRNAs shown.
[1]
State which tissue produces the greatest number of mRNA variants.
[1]
Explain how the data show alternative splicing.
[1]
Suggest one consequence for protein diversity.
[1]
Question 40
Synthetic eukaryotic mRNAs were made with or without a 5′ cap and 3′ polyA tail. Their remaining percentage was measured after incubation in cell extract.
Describe the effect of adding both a cap and a polyA tail on mRNA remaining.
[1]
Compare the stability of capped-only and polyA-only mRNAs.
[1]
Evaluate the claim that post-transcriptional modifications help stabilize mRNA.
[1]
Question 41
Cells were treated with a proteasome inhibitor and the amount of damaged protein and free amino acids was measured.
Describe the effect of proteasome inhibition on damaged protein.
[1]
Describe the effect of proteasome inhibition on free amino acids available for new protein synthesis.
[1]
Suggest why both effects could reduce the ability of the cell to maintain a functional proteome.
[1]
Question 42
Outline transcription as the synthesis of RNA.
[1]
Explain how complementary base pairing and hydrogen bonding contribute to reliable transcription while allowing the DNA template to be reused.
[1]
Question 43
Outline the roles of mRNA and tRNA in translation.
[1]
Explain elongation of a polypeptide at a ribosome.
[1]
Question 44
A pulse-chase experiment followed labelled insulin-related polypeptides in pancreatic beta cells.
Identify the first labelled polypeptide detected.
[1]
Describe the sequence of changes in labelled products over time.
[1]
Deduce why functional insulin is not the immediate product of translation.
[1]
Question 45
State two features of the genetic code.
[1]
Discuss how the genetic code enables cells to produce many different polypeptides and why some mutations do not change a polypeptide.
[1]
Question 46
Outline how an mRNA sequence is translated into a polypeptide sequence.
[1]
Explain how a point mutation can alter protein structure and phenotype, using beta-globin as an example.
[1]
Question 47
Outline what is meant by 5′ and 3′ ends of nucleic acid strands.
[1]
Explain how directionality is important in transcription and translation.
[1]
Question 48
Describe two post-transcriptional modifications of eukaryotic pre-mRNA.
[1]
Discuss how post-transcriptional modification and alternative splicing contribute to gene expression and protein diversity.
[1]
Question 49
Outline initiation of translation.
[1]
Explain the roles of the A, P and E sites of the ribosome during elongation.
[1]
Question 50
Outline the two-stage conversion of pre-proinsulin to insulin.
[1]
Evaluate the statement: “Protein synthesis is complete when translation ends.”
[1]
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