4 questions, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 4
Which statement describes the role of messenger RNA (mRNA) in a eukaryotic cell?
Answer and reasoning
AIt stays in the nucleus, where it is translated by the ribosomes that are found there. A student who thinks translation takes place in the nucleus picks this. In eukaryotic cells the ribosomes that translate mRNA are in the cytoplasm.
BIt carries information from DNA in the nucleus to the ribosomes in the cytoplasm.Correct mRNA is transcribed from a gene's DNA in the nucleus and carries the gene's information to ribosomes in the cytoplasm, where it is translated.
CIt folds up to form the protein whose amino acid sequence it codes for. A student who thinks mRNA itself becomes the protein picks this. mRNA directs the order in which amino acids, brought by tRNAs, are joined; the mRNA does not become the protein.
DIt carries the DNA of a gene out of the nucleus to ribosomes in the cytoplasm. A student who thinks DNA leaves the nucleus to be used at the ribosomes picks this. DNA stays in the nucleus; mRNA carries a copy of its information.
Which statement describes how the DNA of a gene is used during transcription?
Answer and reasoning
AOne of the two DNA strands is used as a template, and the RNA made is identical to it. A student who thinks the RNA copies its template's sequence picks this. The RNA is complementary to the template strand; it matches the other strand, with U in place of T.
BBoth of the DNA strands are used as templates, and the two RNA strands made then pair together. A student who thinks RNA is double-stranded like DNA, with both strands copied as in replication, picks this. Only one strand of a gene is used as the template, and the mRNA made is a single strand.
COne of the two DNA strands is used as a template, and the RNA made is complementary to it.Correct RNA polymerase reads a single template strand of the gene and adds RNA nucleotides complementary to it (U opposite A, A opposite T, C opposite G, G opposite C). The RNA therefore has the same sequence as the other DNA strand, with U in place of T.
DOne of the two DNA strands is converted into RNA, which then leaves the nucleus for the cytoplasm. A student who thinks DNA is turned into RNA picks this. The DNA is not used up or changed: it is read as a template, and a new RNA molecule is built from RNA nucleotides.
The diagram shows both strands of a short section of a gene and the direction in which RNA polymerase moves along the gene as it transcribes this section. Reading from left to right, which sequence and direction describe the RNA transcribed from this section?
Answer and reasoning
ATACGGATC, from 5′ to 3′ A student who thinks RNA contains thymine picks this. RNA contains uracil, so wherever the template has A, the RNA has U, not T.
BUACGGAUC, from 5′ to 3′Correct RNA polymerase reads its template 3′ to 5′, so as it moves to the right it reads strand 2, whose 3′ end is on the left. The RNA is complementary and antiparallel to strand 2, with U opposite A: from left to right it reads UACGGAUC, from 5′ to 3′, the same sequence as strand 1 with U in place of T.
CUACGGAUC, from 3′ to 5′ A student who thinks the RNA runs in the same direction as its template picks this. The bases are right, but the RNA is antiparallel to strand 2, so its 5′ end is on the left.
DAUGCCUAG, from 3′ to 5′ A student who thinks the RNA has the same sequence as its template strand picks this. The RNA is complementary to the template, strand 2: opposite A it has U, and opposite G it has C.
Which statement describes the processing of a primary transcript into mature mRNA in a eukaryotic cell?
Answer and reasoning
AA GTP cap and a poly-A tail are added to the transcript, and its introns are removed.Correct Enzymes modify the primary transcript: a GTP cap is added to its 5′ end, a poly-A tail is added to its 3′ end, and the introns are excised and the exons spliced together.
BA GTP cap and a poly-A tail are added to the gene's DNA, and its introns are then removed. A student who thinks RNA processing changes the gene picks this. Processing acts on the RNA transcript; the gene's DNA keeps its introns and has no cap or tail.
CThe introns, the GTP cap and the poly-A tail are all removed before the mRNA is translated. A student who thinks every processing step removes something picks this. The cap and the tail are added to the mRNA and stay on it; only the introns are removed.
DA GTP cap and a poly-A tail are added, and the introns are kept so that they can be translated. A student who thinks introns stay in the mature mRNA picks this. Introns are excised during processing, and the exons are spliced together.
In preparation: 0 of 4 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
6.3.A.1 RNA structure and function Fix
RNA structure and function
An RNA molecule is a single strand whose function depends on its base sequence and on the shape it folds into; the shape is held by base pairing between different parts of the same strand.
Messenger RNA (mRNA)
RNA that carries the information of a gene from DNA to the ribosomes. In eukaryotic cells it is made in the nucleus and carries the information to ribosomes in the cytoplasm, where its sequence directs the order of amino acids.
Codon
A sequence of three mRNA bases. During translation, a codon that specifies an amino acid base pairs with the complementary anticodon of a tRNA.
Transfer RNA (tRNA)
An RNA molecule that binds a specific amino acid and has an anticodon that base pairs with an mRNA codon, so that it is recruited to the ribosome and adds its amino acid where the mRNA sequence specifies.
Anticodon
The three-base sequence of a tRNA that base pairs with a codon; it is complementary to the codon and runs in the opposite direction.
Ribosomal RNA (rRNA)
RNA molecules that, together with proteins, make up ribosomes and are functional parts of them; rRNA is not translated.
Students often think A gene's DNA leaves the nucleus and goes to the ribosomes, where it is used to make protein. In fact No. In eukaryotic cells, DNA stays in the nucleus. mRNA transcribed from it carries the information to ribosomes in the cytoplasm.
Students often think Ribosomes translate mRNA inside the nucleus, close to the DNA. In fact No. In eukaryotic cells, mRNA carries information from DNA in the nucleus to ribosomes in the cytoplasm, where it is translated.
6.3.A.2 Transcription Fix
Transcription
The synthesis of an RNA molecule by RNA polymerase, which uses a single template strand of a gene's DNA to direct which bases are included in the RNA.
Template strand
The one DNA strand of a gene that RNA polymerase reads. The RNA made is complementary to it, so it has the same sequence as the other DNA strand, with U in place of T.
Students often think RNA contains thymine, so it is built from the same four bases as DNA. In fact No. RNA contains uracil (U) in place of thymine, so where the DNA template has A, the RNA has U.
Students often think The RNA made in transcription has the same base sequence as the template strand it is copied from, with U in place of T. In fact No. The RNA is complementary to the template strand. It has the same sequence as the other DNA strand of the gene, with U in place of T.
6.3.A.3 RNA polymerase Fix
RNA polymerase
The enzyme that synthesizes RNA, adding RNA nucleotides complementary to the template strand. It reads the template 3′ to 5′ and builds the RNA 5′ to 3′.
Students often think Paired nucleic acid strands, such as an RNA and its DNA template or an anticodon and its codon, run in the same 5′ to 3′ direction. In fact No. Base-paired nucleic acid strands are antiparallel: an RNA runs opposite to its DNA template strand, and an anticodon runs opposite to the codon it pairs with.
6.3.A.4 Primary transcript Fix
Primary transcript
In eukaryotic cells, the RNA first made when a gene is transcribed, before it is modified by enzymes into mature mRNA.
RNA processing
The enzyme-mediated modifications of a eukaryotic primary transcript: addition of a GTP cap and a poly-A tail, and the excision of introns with splicing of exons.
Poly-A tail
A string of adenine-containing nucleotides added to the 3′ end of a eukaryotic mRNA; it makes the mRNA more stable.
GTP cap
A modified guanine nucleotide, added from GTP to the 5′ end of a eukaryotic mRNA; it helps ribosomes recognize the mRNA.
Intron
A section of a primary transcript that is excised during RNA processing.
Exon
A section of a primary transcript that can be retained in the mature mRNA; retained exons are spliced together after the introns are excised.
Alternative splicing
The excision of introns together with the splicing and retention of different combinations of exons, so that one gene's primary transcript gives rise to different versions of the mature mRNA, and so of the protein.
Students often think RNA processing changes the gene's DNA: introns are cut out of the gene, and the cap and tail are added to it. In fact No. RNA processing acts on the RNA transcript. The gene's DNA keeps its introns, and the GTP cap and poly-A tail are added to the mRNA, not to the DNA.
Students often think Introns stay in the mature mRNA and are translated along with the exons. In fact No. In the processing of eukaryotic mRNA, introns are excised and exons are spliced together, so the mature mRNA that is translated is made of the retained exons.
11 more questions. Every wrong answer here is a real mistake students make, and you see why it is wrong as soon as you answer.
Question 1 of 11
In a test tube translation system, the tRNAs with the anticodon 3′-ACG-5′ normally carry the amino acid cysteine, and they are the only tRNAs in the system that pair with the codon 5′-UGC-3′. Before translation, the cysteine attached to these tRNAs is chemically changed into a different amino acid, alanine; the tRNAs themselves are unchanged. An mRNA containing the codon 5′-UGC-3′ is then translated. Which prediction about the polypeptide made is correct?
Answer and reasoning
AAlanine will be placed there, as the tRNA brings the amino acid it carries.Correct The anticodon 3′-ACG-5′ base pairs with the complementary codon 5′-UGC-3′, and the tRNA delivers whatever amino acid is attached to it. The ribosome matches codon with anticodon, not with the amino acid, so alanine is placed at each UGC codon.
BCysteine will be placed there, as the codon binds cysteine directly. A student who thinks a codon recognizes its amino acid directly picks this. Codons pair with tRNA anticodons; the amino acid is attached to the tRNA and is not read by the mRNA.
CCysteine will be placed there, as the anticodon still specifies cysteine. A student who thinks the anticodon fixes which amino acid is delivered picks this. The anticodon determines where the tRNA binds; the amino acid delivered is the one attached to the tRNA, here alanine.
DNo amino acid will be placed there, as the ribosome rejects the altered tRNA. A student who thinks the ribosome checks each amino acid picks this. The ribosome checks only the pairing of anticodon and codon, which is unchanged, so the altered tRNA is used and alanine is added.
Cells of a hypothetical species of yeast were given radioactively labeled uracil, a base found in RNA but not in DNA, for 5 minutes. They were then moved to a medium containing only unlabeled uracil. The graph shows the percentage of the cells' labeled RNA found in the nucleus and in the cytoplasm at times after labeling ended. Which explanation of the data is consistent with the role of mRNA?
Answer and reasoning
ADNA moved from the nucleus into the cytoplasm, where it was transcribed into RNA. A student who thinks DNA leaves the nucleus to be used at the ribosomes picks this. After labeling ended, only unlabeled uracil was available, so RNA made in the cytoplasm then could not be labeled; the labeled RNA in the cytoplasm must have come from the nucleus.
BRNA was translated in the nucleus and then moved into the cytoplasm to be broken down. A student who thinks translation happens in the nucleus picks this. In eukaryotic cells, mRNA is translated by ribosomes in the cytoplasm; RNA moves out of the nucleus to be used there.
CRNA in the nucleus was converted into protein, which then moved into the cytoplasm. A student who thinks RNA turns into protein picks this. The graph tracks labeled RNA, which appears in the cytoplasm as RNA; RNA is not converted into protein.
DRNA made in the nucleus moved out into the cytoplasm, where the ribosomes are found.Correct Labeled RNA was made only during the 5-minute labeling period, and at first 90% of it was in the nucleus. Over the next hour the percentage in the nucleus fell as the percentage in the cytoplasm rose, so RNA made in the nucleus moved to the cytoplasm. This fits mRNA carrying information from DNA in the nucleus to ribosomes in the cytoplasm.
The diagram shows a tRNA whose anticodon base pairs with the highlighted codon of an mRNA. Reading from left to right, which sequence and direction describe the tRNA's anticodon?
Answer and reasoning
ACTA, from 3′ to 5′ A student who thinks RNA contains thymine picks this. A tRNA is RNA, so opposite A in the codon its anticodon has U, not T.
BGAU, from 5′ to 3′ A student who thinks an anticodon has the same sequence as its codon picks this. The anticodon must be complementary to the codon in order to base pair with it.
CCUA, from 5′ to 3′ A student who thinks paired strands run in the same direction picks this. The bases are right, but the anticodon is antiparallel to the codon, so its 3′ end lies opposite the codon's 5′ end.
DCUA, from 3′ to 5′Correct The anticodon is complementary to the codon GAU (C opposite G, U opposite A, A opposite U) and antiparallel to it. The codon runs 5′ to 3′ from left to right, so the anticodon above it runs 3′ to 5′: CUA, from 3′ to 5′.
The same mRNA, made either with or without a poly-A tail, was injected into cells of a hypothetical species of frog, and the percentage of each mRNA remaining in the cells was measured over 8 hours. The graph shows the results. Which statement describes the data?
Answer and reasoning
AThe tail-less mRNA fell to half its starting level in about 2 hours, faster than the other.Correct The dashed line falls from 100% to 50% in the first 2 hours, while the mRNA with a tail still has 90% remaining at 2 hours and 66% at 8 hours. The mRNA without a poly-A tail was broken down much faster, consistent with the tail making mRNA more stable.
BThe mRNA without a tail fell by the same amount, about 25 percentage points, in each 2-hour interval. A student who expects a halving quantity to fall by a fixed amount picks this. The tail-less mRNA fell by 50, then 25, then 12 and then 7 percentage points: it lost about half of what remained in each 2-hour interval.
CThe mRNA without a tail had been broken down completely by 4 hours, after two of its half-lives. A student who thinks two half-lives remove everything picks this. At 4 hours, two half-lives, 25% of the tail-less mRNA remained, a quarter of the starting amount.
DThe mRNA with a tail was broken down more, as its line is higher at every time after 0 hours. A student who reads a higher line as more of the process happening picks this. The axis shows mRNA remaining, so the higher line means that less of the mRNA with a tail was broken down.
In cells of a hypothetical species of animal, a mutation prevents a poly-A tail from being added to the mRNA of gene H. Gene H is still transcribed at its normal rate. Which prediction is correct?
Answer and reasoning
AShorter H protein would be made, because the tail codes for the protein's last amino acids. A student who thinks the poly-A tail is translated picks this. The tail is added after transcription and is not translated, so missing it does not remove amino acids from the protein.
BThe same amount of H protein would be made, as the cell would add extra caps instead. A student who explains cell processes by what the cell needs picks this. Nothing replaces the missing tail; the H mRNA is simply less stable.
CLess H protein would be made, because each H mRNA molecule would be broken down sooner.Correct The poly-A tail makes mRNA more stable. Without it, each H mRNA molecule would be broken down sooner, so fewer H mRNA molecules would be present at any time to be translated, and less H protein would be made.
DThe same amount of H protein would be made, because the tail is removed before it is translated. A student who thinks every processing addition is removed again, like introns, picks this. The poly-A tail stays on the mRNA, where it makes the mRNA more stable, so losing it reduces the amount of H protein made.
A researcher wants to test the hypothesis that the GTP cap helps ribosomes recognize mRNA. She has test tube systems that carry out translation. Which experimental design would best test this hypothesis?
Answer and reasoning
AAdd a capped mRNA of one gene and an uncapped mRNA of another gene, and compare the protein made. A student who thinks groups can differ in more than one variable picks this. The two mRNAs differ in their sequence as well as in the cap, so a difference in protein could be caused by either.
BAdd the same capped mRNA to two identical systems, and compare the amount of protein made in each. A student who thinks repeating a treatment tests a variable picks this. Both systems receive capped mRNA, so the comparison shows only how much results vary, not what the cap does.
CRemove the cap sequence from the gene's DNA in some cells, and compare the amount of mRNA they make. A student who thinks the cap is part of the gene's DNA picks this. The cap is added to the mRNA after transcription, so there is no cap sequence in the gene; and the hypothesis concerns translation, not how much mRNA is made.
DAdd equal amounts of the same mRNA, with or without a cap, to identical systems and compare the protein made.Correct The two groups differ only in the presence of the cap: the same mRNA, the same amount and identical translation systems. If ribosomes recognize capped mRNA more readily, more protein should be made from it, so any difference in protein can be attributed to the cap.
The diagram shows the primary transcript of gene F, with its exons (E) and introns (I), and the mature mRNAs found in two cell types of a hypothetical species of animal. Which statement best explains how the two mature mRNAs are produced?
Answer and reasoning
AExon 3 has been cut out of gene F's DNA in the cells of cell type 2 but not cell type 1. A student who thinks splicing removes sequences from the gene's DNA picks this. The model shows the same primary transcript, including E3, in both cell types; exon 3 is removed from the RNA, not from the gene.
BIntron 3 is retained in cell type 2 and is translated there in place of exon 3. A student who thinks introns stay in the mature mRNA picks this. The cell type 2 mRNA in the model contains only exons, E1, E2 and E4; all three introns have been excised.
CExon 3 is excised with the introns in cell type 2 but retained in cell type 1.Correct Both mature mRNAs come from the same primary transcript. In cell type 1 all four exons are retained and spliced together; in cell type 2 exon 3 is excised with the introns, so E2 is spliced directly to E4. This is alternative splicing.
DThe cell type 2 mRNA comes from another gene, as gene F makes only one mRNA. A student who thinks each gene produces only one kind of mRNA picks this. The model shows both mature mRNAs arising from the same primary transcript of gene F, by alternative splicing.
Equal amounts of the same mRNA, made either with or without a GTP cap, were added to two identical test tube translation systems prepared from a hypothetical species of plant. The table shows the results after 60 minutes. By what percentage was the amount of protein made from the uncapped mRNA lower than the amount made from the capped mRNA?
Answer and reasoning
A36% A student who reports the change in the amount of protein, 120 − 84 = 36 ng, as the percent change picks this. The change must be divided by the original amount: 36/120 × 100 = 30%.
B30%Correct Percent decrease = (120 − 84)/120 × 100 = 30%. Almost the same percentage of each mRNA remained (95% and 94%), so less protein was made from the uncapped mRNA even though as much of it was present, which fits the cap's role in helping ribosomes recognize mRNA.
C43% A student who divides the change by the new value picks this: 36/84 × 100 = 43%. The question compares with the capped mRNA, so the reference value is 120 ng.
D70% A student who gives the new value as a percentage of the original picks this: 84/120 × 100 = 70%. The uncapped mRNA made 70% as much protein, which is 30% less.
Working From the table, 120 ng of protein was made from the capped mRNA and 84 ng from the uncapped mRNA. Percent decrease = (original − new)/original × 100 = (120 − 84)/120 × 100 = 36/120 × 100 = 30%. Almost the same percentage of each mRNA remained (95% and 94%), so the difference in protein is not explained by breakdown of the uncapped mRNA. Distractors: reporting the 36 ng difference as a percentage gives 36%; dividing the difference by the new value gives 36/84 × 100 = 42.9%, shown as 43%; giving the new value as a percentage of the original gives 84/120 × 100 = 70%.
In a hypothetical species of bacterium, a mutation changes three bases in the gene for one kind of tRNA. The changed bases are outside the anticodon, and the tRNA has the same number of nucleotides as before, but it no longer works in translation. Which statement best explains why the tRNA no longer works?
Answer and reasoning
AThe changed bases altered the protein that the tRNA codes for, so the protein fails to work. A student who thinks every RNA is translated into a protein picks this. tRNA is not translated; it works directly as a folded RNA molecule.
BThe tRNA now carries a different amino acid, which the ribosome detects and rejects. A student who thinks the ribosome checks the amino acid on each tRNA picks this. The ribosome checks codon–anticodon pairing, not the amino acid; changed bases outside the anticodon act by altering the base pairing that holds the tRNA in its working shape.
CThe changed bases altered pairing within the tRNA, so it no longer folds into its working shape.Correct A tRNA is a single RNA strand that folds because bases in different parts of the strand pair with each other. Its base sequence determines this folded structure, and the structure is needed for it to carry its amino acid and fit into the ribosome. Changed bases that took part in these pairs alter the pairing, so the strand no longer folds into its working shape, and the tRNA loses its function.
DThe tRNA is unable to pair with a second RNA strand to form a double helix, as DNA does. A student who thinks RNA is a double helix like DNA picks this. A tRNA is a single strand whose shape comes from base pairing between parts of that same strand, not from pairing with a second strand.
The graph shows, for four tissues of a hypothetical species of mammal, the percentage of gene F's mature mRNA molecules that include exon 3. Which statement is supported by the data?
Answer and reasoning
AEach tissue makes only one version of the gene F mRNA, either with or without exon 3. A student who thinks a gene makes only one kind of mRNA picks this. Every bar is between 0% and 100%, so every tissue makes both versions.
BLiver cells lack exon 3 in their copy of gene F, unlike the cells of the brain. A student who thinks different cell types contain different versions of a gene picks this. 10% of liver mRNAs include exon 3, so liver cells must have exon 3 in their gene F.
CBrain cells contain more gene F mRNA than liver cells do, as their bar is much taller. A student who reads a percentage as an amount picks this. The bars show what percentage of each tissue's gene F mRNA includes exon 3, not how much gene F mRNA each tissue contains.
DIn every tissue mRNAs with and without exon 3 are made, but in proportions that differ by tissue.Correct Every bar is above 0%, from 10% in liver to 90% in brain, so each tissue makes some mRNAs with exon 3 and some without, in different proportions. One gene gives rise to different mature mRNAs by alternative splicing, regulated differently in different tissues.
Ribosomes from a hypothetical species of bacterium were treated in three ways. Each treatment enzyme was then removed, and the ribosomes' ability to form peptide bonds between amino acids was measured. The table shows the results. Which claim is best supported by the data?
Answer and reasoning
AThe ribosome's RNA is needed for it to form peptide bonds between amino acids.Correct Breaking down the ribosome's RNA left only 3% of peptide bond formation, while breaking down its protein left 80%. The rRNA is therefore a functional part of the ribosome, needed for peptide bonds to form, not just a scaffold.
BThe ribosome's proteins form peptide bonds, and its RNA only holds them in place. A student who thinks all of a ribosome's work is done by protein picks this. Breaking down the protein left 80% of the activity, so the proteins cannot be doing all of the work, while breaking down the RNA almost abolished it.
CThe ribosome's RNA codes for a protein that forms the peptide bonds. A student who thinks every RNA is translated into a protein picks this. If a protein made from the rRNA formed the bonds, breaking down the ribosome's protein should have reduced activity sharply; rRNA is not translated.
DThe ribosome's RNA is converted into the peptide chain as each bond forms. A student who thinks RNA is turned into protein picks this. The amino acids joined by peptide bonds come from tRNAs; the ribosome's RNA is not converted into protein.
Compiled from the AP Biology Course and Exam Description (effective Fall 2025) and our question bank · Specialist review in progress. How these pages are made · Free, no account
