Question 1
What is the role of RNA polymerase during transcription?
A.
It catalyses formation of an RNA strand using a DNA template.
B.
It removes introns from mature mRNA in the cytoplasm.
C.
It attaches a specific amino acid to a tRNA molecule.
D.
It joins amino acids into a polypeptide at the ribosome.
Question 2
A short section of a DNA template strand has the base sequence 3-TAC GGA-5. What RNA sequence is transcribed from it?
A.
5-AUG CCU-3
B.
5-TAC GGA-3
C.
5-AUG CCT-3
D.
5-UAC GGA-3
Question 3
A pancreatic beta cell and a neurone contain the same inherited genome but produce different proteins. What best explains this difference?
A.
Different bases are present in the DNA of each cell type.
B.
Different genetic codes are used in the two cell types.
C.
Different ribosomes permanently alter the DNA template.
D.
Different genes are transcribed in the two cell types.
Question 4
What is the role of tRNA during translation?
A.
It carries a specific amino acid and has an anticodon that pairs with mRNA.
B.
It breaks peptide bonds in proteins selected for recycling.
C.
It forms the small ribosomal subunit that binds mRNA.
D.
It provides the DNA template used to synthesize mRNA.
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Question 5
What correctly describes directionality during transcription?
A.
The ribosome reads DNA 5 to 3 before RNA polymerase translates it.
B.
Both RNA and the DNA template are synthesized 5 to 3 during transcription.
C.
RNA is synthesized 5 to 3 while the DNA template is read 3 to 5.
D.
RNA is synthesized 3 to 5 while the DNA template is read 5 to 3.
Question 6
A mutation prevents a transcription factor from binding to the promoter of a gene. What is the most direct likely effect?
A.
Immediate removal of exons from the mature mRNA
B.
Failure of peptide bonds to form at the ribosome
C.
Reduced initiation of transcription of that gene
D.
Replacement of uracil with thymine in the transcript
Question 7
Which DNA sequence is a non-coding sequence that protects the ends of eukaryotic chromosomes?
A.
Telomere
B.
Exon
C.
Anticodon
D.
Codon
Question 8
A single-base substitution changes the mRNA codon GAA to GAG, but both codons specify glutamic acid. What feature of the genetic code is shown?
A.
Complementarity
B.
Universality
C.
Directionality
D.
Degeneracy
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Question 9
What processing occurs during post-transcriptional modification of eukaryotic pre-mRNA?
A.
Amino acids are joined by peptide bonds and a signal sequence is removed.
B.
The ribosome attaches to the promoter and moves to the start codon.
C.
Exons are removed, introns are spliced together, and thymine bases are added at both ends.
D.
Introns are removed, exons are spliced together, and a 5 cap and 3 polyA tail are added.
Question 10
How can one eukaryotic gene code for different polypeptide variants?
A.
Telomeres can be inserted into coding sequences before translation.
B.
The ribosome can choose a different genetic code for each tissue.
C.
Different combinations of exons from the same pre-mRNA can be joined during splicing.
D.
RNA polymerase can translate the same mRNA in opposite directions.
Question 11
The diagram shows part of a gene during transcription.
State the role of RNA polymerase in transcription.
[1]
Outline how the DNA template strand determines the base sequence of the RNA transcript.
[2]
Explain why the DNA molecule can be transcribed many times without being used up.
[1]
Question 12
A liver cell and a neurone from the same person contain the same genome, but they produce different sets of proteins.
Define gene expression.
[1]
Explain why the two cell types can produce different proteins despite having the same DNA sequence.
[2]
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Question 13
The diagram shows molecules involved in translation at a ribosome.
State the role of mRNA in translation.
[1]
Outline the roles of the small and large ribosomal subunits in translation.
[2]
Explain why tRNA is described as an adaptor molecule in translation.
[1]
Question 14
A cell begins producing a protein only after a specific regulatory protein binds near the start of the gene.
Define promoter.
[1]
Explain how transcription factors can affect expression of a gene.
[2]
Question 15
The diagram shows a short section of a DNA transcription bubble. One DNA strand is labelled as the template strand and a growing RNA strand contains three blank positions.
State the RNA base sequence that would be synthesized from the template strand shown.
[1]
Explain how complementary base pairing contributes to the reliability of transcription.
[2]
Suggest why the DNA base sequence is unchanged after the RNA polymerase has passed.
[1]
Question 16
A cell-free translation system was prepared using purified components. The graph shows polypeptide production when one component was omitted from the complete mixture.
Describe the effect of omitting mRNA from the translation mixture.
[1]
Explain the roles of mRNA and tRNA in translation.
[2]
State one role of a ribosome in translation.
[1]
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Question 17
A non-dividing somatic cell was monitored while the same gene was transcribed repeatedly. The graph shows the number of RNA transcripts made and the measured similarity of the DNA template sequence to its original sequence.
Transcription cycle / number | Total RNA transcripts made / number | DNA template similarity to original sequence / % |
|---|---|---|
1 | 1 | 100 |
2 | 2 | 100 |
3 | 3 | 100 |
4 | 4 | 100 |
5 | 5 | 100 |
6 | 6 | 100 |
Describe what happens to the DNA template sequence during repeated transcription.
[1]
Explain why conservation of the DNA template is important in a non-dividing somatic cell.
[2]
State the enzyme that catalyses RNA synthesis during transcription.
[1]
Question 18
The mRNA sequence 5-AUG UUU GGC UAA-3 is translated using the genetic code. AUG codes for methionine, UUU for phenylalanine, GGC for glycine and UAA is a stop codon. What is the amino acid sequence produced?
A.
Methionine--phenylalanine--glycine
B.
Tyrosine--lysine--proline
C.
Methionine--phenylalanine--glycine--stop
D.
Phenylalanine--glycine only
Question 19
During elongation in translation, a charged tRNA carrying the next amino acid enters a ribosome. At which site does it first bind?
A.
P site
B.
E site
C.
A site
D.
Promoter site
Question 20
A genetic code table using mRNA codons is provided.
Deduce the amino acid sequence translated from this mRNA sequence:
5-AUG UUU CCA GAA UGA-3
[1]
State why a genetic code table should be read using mRNA codons rather than DNA triplets.
[1]
Outline one feature of the genetic code that is shown by several codons coding for the same amino acid.
[1]
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Question 21
The diagram represents elongation during translation.
State what is meant by a codon.
[1]
Explain how the next amino acid is brought into the correct position during elongation.
[2]
State the reaction catalysed by the ribosome that lengthens the growing polypeptide.
[1]
Question 22
The diagram shows the direction of transcription for a short gene.
State what is meant by directionality in a nucleic acid strand.
[1]
Explain what is meant by 5 to 3 transcription.
[2]
State the direction in which the ribosome reads mRNA during translation.
[1]
Question 23
A eukaryotic pre-mRNA transcript contains exons and introns and is processed before leaving the nucleus.
State one type of non-coding DNA sequence in eukaryotes, other than introns.
[1]
Outline what happens to introns and exons during splicing.
[2]
State one function of the 5 cap or the 3 polyA tail.
[1]
Question 24
The diagram shows alternative splicing of one pre-mRNA transcript.
State what is meant by alternative splicing.
[1]
Explain how alternative splicing allows one gene to code for more than one polypeptide.
[2]
Suggest one advantage to a cell of alternative splicing.
[1]
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Question 25
Insulin is synthesized as an inactive polypeptide and becomes functional only after modification. Cells also continually break down some proteins to sustain a functional proteome.
Outline the two-stage modification of pre-proinsulin to functional insulin.
[2]
State why post-translational modification is needed for many proteins.
[1]
Explain the role of proteasomes in maintaining a functional proteome.
[1]
Question 26
The table shows relative mRNA abundance for four genes in three human cell types isolated from the same individual.
Gene | Pancreatic beta cells | Hepatocytes | Skeletal muscle cells |
|---|---|---|---|
INS | 100 | 1 | 1 |
ALB | 1 | 96 | 1 |
ACTA1 | 1 | 2 | 94 |
GAPDH | 48 | 47 | 49 |
Identify the gene that is most strongly expressed in pancreatic beta cells.
[1]
Explain why mRNA abundance is evidence that a gene is being expressed.
[2]
Suggest why different cell types from the same individual can produce different proteins.
[1]
Question 27
The diagram shows three successive stages during elongation of a polypeptide on the same mRNA molecule.
Describe the movement of the ribosome between the stages shown.
[1]
Explain how the polypeptide grows during elongation.
[2]
State the anticodon that would pair with the mRNA codon UAC shown in the diagram.
[1]
Question 28
The diagram shows stages in initiation of translation on a eukaryotic mRNA and the positions of tRNAs during the first elongation cycle.
State the anticodon of the initiator tRNA that pairs with the AUG start codon.
[1]
Outline two events that occur during initiation of translation before elongation begins.
[2]
Explain the roles of the A, P and E sites during elongation.
[2]
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Question 29
A point mutation in the beta-globin gene can affect the structure of haemoglobin. In one allele, an mRNA codon specifying glutamic acid is changed to a codon specifying valine.
State what is meant by a point mutation.
[1]
Explain how this point mutation can change the primary structure of beta-globin.
[2]
Suggest one way in which this amino acid substitution can affect the phenotype of red blood cells.
[1]
Question 30
Translation initiation positions the ribosome and tRNAs so that the correct reading frame is used.
Outline two events that occur during initiation of translation in eukaryotic cells.
[2]
State the roles of the A site and E site of the ribosome during elongation.
[2]
Question 31
The table gives a short section of mRNA from a gene and two point-mutated versions. A genetic code extract for the relevant mRNA codons is also shown.
Section | Item | 1st codon | 2nd codon | 3rd codon | 4th codon | Amino acid |
|---|---|---|---|---|---|---|
mRNA | Normal | AUG | GAA | UUU | UGA | — |
mRNA | Point mutation 1 | AUG | GAG | UUU | UGA | — |
mRNA | Point mutation 2 | AUG | GUA | UUU | UGA | — |
Genetic code | AUG | — | — | — | — | Methionine |
Genetic code | GAA | — | — | — | — | Glutamic acid |
Genetic code | GAG | — | — | — | — | Glutamic acid |
Genetic code | GUA | — | — | — | — | Valine |
Genetic code | UUU | — | — | — | — | Phenylalanine |
Genetic code | UGA | — | — | — | — | Stop |
Deduce the amino acid sequence encoded by the normal mRNA sequence, stopping at the first stop codon.
[2]
Explain why one of the point mutations shown is described as silent.
[1]
Suggest how the other point mutation could affect protein structure.
[2]
Question 32
The diagram shows a gene being transcribed and the resulting mRNA being translated. The 5' and 3' ends of the DNA template strand, RNA transcript and mRNA are labelled.
Deduce the direction in which the DNA template is read and the RNA transcript is synthesized.
[2]
Explain why mRNA must be translated in one consistent direction.
[1]
Suggest what would happen if a ribosome translated the mRNA from the opposite end.
[1]
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Question 33
Reporter constructs were made using the same coding sequence attached to different promoter regions. The graph shows reporter mRNA abundance with and without a transcription factor.
Identify the construct expected to have the greatest reporter mRNA abundance when the transcription factor is present.
[1]
Explain how a transcription factor can increase transcription at a promoter.
[2]
Suggest why reporter mRNA abundance can change even though the coding sequence is unchanged.
[1]
Question 34
RNA sequencing of two tissues detected two mature mRNA variants from the same gene. The exon map and relative abundance of each variant are shown.
mRNA variant | Exon 1 | Exon 2 | Exon 3 | Exon 4 | Relative abundance / % |
|---|---|---|---|---|---|
Variant 1 | present | present | present | present | 60 |
Variant 2 | present | present | absent | present | 40 |
Identify the exon that is included in variant 1 but absent from variant 2.
[1]
Explain how the same gene can produce two different mature mRNA molecules.
[2]
Suggest why the two mRNA variants may produce polypeptides with different functions.
[1]
Question 35
A pulse-chase experiment followed newly synthesized insulin-related polypeptides in pancreatic beta cells. The graph shows relative amounts of pre-proinsulin, proinsulin and insulin over time after labelling.
Describe the sequence of insulin-related molecules shown by the pulse-chase data.
[1]
Explain why translation alone does not produce functional insulin.
[2]
Suggest how proteasomes help sustain a functional proteome in the same cell.
[1]
Question 36
The diagram shows transcription of a protein-coding gene in a somatic cell.
I.
Explain the role of RNA polymerase in the process shown.
[2]
II.
Explain how hydrogen bonding contributes to the reliability of transcription.
[2]
Discuss the importance of the DNA template remaining unchanged during repeated transcription in long-lived somatic cells.
[2]
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Question 37
The graph shows relative mRNA abundance for three genes in three specialised human cell types: a neurone, a liver cell and a pancreatic beta cell.
I.
State what high mRNA abundance for one gene in one cell type indicates about that gene.
[1]
II.
Explain why different mRNA abundance can occur in cells with the same genome.
[2]
Discuss why transcription is a key stage at which expression of a protein-coding gene can be controlled.
[3]
Question 38
An mRNA sequence is shown below. A standard genetic code table of mRNA codons is also provided.
5'-AUG UUU GGC CAA UGA-3'
mRNA codon | Amino acid |
|---|---|
UUU | Phe |
UUC | Phe |
UUA | Leu |
UUG | Leu |
UCU | Ser |
UCC | Ser |
UCA | Ser |
UCG | Ser |
UAU | Tyr |
UAC | Tyr |
UAA | Stop |
UAG | Stop |
UGU | Cys |
UGC | Cys |
UGA | Stop |
UGG | Trp |
CUU | Leu |
CUC | Leu |
CUA | Leu |
CUG | Leu |
CCU | Pro |
CCC | Pro |
CCA | Pro |
CCG | Pro |
CAU | His |
CAC | His |
CAA | Gln |
CAG | Gln |
CGU | Arg |
CGC | Arg |
CGA | Arg |
CGG | Arg |
AUU | Ile |
AUC | Ile |
AUA | Ile |
AUG | Met |
ACU | Thr |
ACC | Thr |
ACA | Thr |
ACG | Thr |
AAU | Asn |
AAC | Asn |
AAA | Lys |
AAG | Lys |
AGU | Ser |
AGC | Ser |
AGA | Arg |
AGG | Arg |
GUU | Val |
GUC | Val |
GUA | Val |
GUG | Val |
GCU | Ala |
GCC | Ala |
GCA | Ala |
GCG | Ala |
GAU | Asp |
GAC | Asp |
GAA | Glu |
GAG | Glu |
GGU | Gly |
GGC | Gly |
GGA | Gly |
GGG | Gly |
I.
Determine the amino acid sequence translated from the mRNA sequence.
[1]
II.
Determine the DNA template sequence for the first four codons of this mRNA.
[1]
Explain why codons consist of three bases and why the genetic code is described as degenerate.
[3]
Suggest why the near universality of the genetic code is useful in biotechnology.
[1]
Question 39
The diagram summarizes regions of a eukaryotic gene and the RNA molecules detected before and after processing in the nucleus.
Region | Genomic DNA | pre-mRNA | mature mRNA |
|---|---|---|---|
Promoter/regulatory sequence | Present | Absent | Absent |
Exon 1 | Present | Present | Present |
Intron | Present | Present | Absent |
Exon 2 | Present | Present | Present |
5' cap | Absent | Absent | Present |
3' polyA tail | Absent | Absent | Present |
Identify two regions in the diagram that are non-coding DNA sequences.
[2]
Explain why the mature mRNA is shorter than the pre-mRNA in the diagram.
[2]
State one function of the 5' cap or the 3' polyA tail shown on the mature mRNA.
[1]
Question 40
The diagram shows a ribosome translating an mRNA molecule. Two tRNA molecules are positioned within the large ribosomal subunit.
I.
Explain the different roles of mRNA and tRNA in the process shown.
[2]
II.
Explain why two tRNA molecules must be held simultaneously by the large ribosomal subunit during elongation.
[2]
Explain the stepwise movement of the ribosome during elongation of a polypeptide.
[3]
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Question 41
A point mutation in a DNA template strand changes one triplet in the beta-globin gene. The original DNA template triplet is CTC and the mutated DNA template triplet is CAC.
I.
Determine the original and mutated mRNA codons transcribed from these DNA template triplets.
[2]
II.
Using the genetic code, state the change in amino acid caused by this mutation.
[1]
Explain how this single base substitution can lead to a change in phenotype.
[3]
Question 42
A student compared the roles of complementary base pairing in transcription and translation.
I.
Outline complementary base pairing during transcription.
[2]
II.
Outline complementary base pairing during translation.
[2]
Compare the importance of hydrogen bonding in transcription and translation.
[3]
Question 43
A researcher proposed that a ribosome could translate an mRNA molecule equally well from either end because the same bases are present.
I.
Explain what is meant by 5' to 3' transcription.
[2]
II.
State the direction in which ribosomes translate mRNA.
[1]
Evaluate the researcher's proposal.
[3]
Question 44
A promoter region upstream of a eukaryotic gene was tested using a reporter protein. The graph shows reporter protein production with an intact promoter, with a promoter deletion and with an intact promoter plus an added transcription factor.
I.
State the function of a promoter.
[1]
II.
Explain how transcription factors can affect transcription at a promoter.
[2]
Discuss how a mutation in a promoter could change protein production without changing the amino acid sequence coded by the gene.
[3]
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Question 45
A simplified eukaryotic chromosome region is shown. Several DNA regions are labelled: a promoter, an intron, a telomere, a gene for tRNA and an exon of a protein-coding gene.
I.
Identify two labelled regions that are non-coding sequences but have regulatory or structural roles.
[2]
II.
Identify two labelled regions that are transcribed but are not translated into polypeptide.
[2]
Explain why non-coding DNA sequences should not be described as having no function.
[3]
Question 46
The diagram shows initiation of translation followed by early elongation on a eukaryotic mRNA molecule.
I.
Explain how translation is initiated.
[3]
II.
Explain the roles of the A, P and E sites during elongation.
[3]
Suggest why starting translation at the wrong AUG codon could alter the entire polypeptide.
[1]
Question 47
The diagram shows processing of a eukaryotic pre-mRNA transcript before it leaves the nucleus. A second diagram shows that the same pre-mRNA can be spliced in two different ways.
I.
Identify three post-transcriptional modifications shown in the first diagram.
[3]
II.
Explain how these modifications prepare mRNA for translation.
[2]
Discuss how alternative splicing can increase protein diversity in a cell.
[3]
Question 48
The flowchart shows events after translation of insulin mRNA in a pancreatic beta cell, together with protein turnover by proteasomes.
I.
Explain the conversion of pre-proinsulin to proinsulin.
[2]
II.
Explain the conversion of proinsulin to functional insulin.
[2]
Evaluate the statement that protein synthesis alone is sufficient to maintain a functional proteome.
[4]
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