4 questions, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 4
Which statement describes promoters and enhancers?
Answer and reasoning
AThey are proteins that bind to DNA and help RNA polymerase to begin the transcription of a gene. A student who confuses regulatory sequences with the proteins that bind to them picks this. Promoters and enhancers are DNA sequences; transcription factors are the proteins that bind to them.
BThey are parts of a gene's coding sequence that are transcribed and then translated into the protein. A student who thinks every sequence linked with a gene codes for part of its protein picks this. Promoters and enhancers control transcription; they are not translated into the gene's protein.
CThey are DNA sequences that must lie upstream of a gene, before its transcription start site. A student who generalizes from diagrams of a promoter just upstream of a gene picks this. Promoter and enhancer sequences can be upstream or downstream of the transcription start site.
DThey are stretches of DNA that RNA polymerase and transcription factors bind to when transcription begins.Correct Promoters and enhancers are regulatory DNA sequences. RNA polymerase and transcription factors bind to them to initiate transcription, and they can lie upstream or downstream of the transcription start site.
The model shows how a repressor protein controls the transcription of gene R in a hypothetical species of yeast. Based on the model, which statement describes how the repressor decreases the expression of gene R?
Answer and reasoning
AIt breaks down gene R's mRNA as soon as each mRNA molecule has been transcribed from the gene. A student who thinks a repressor works by destroying the gene's product picks this. The model shows the repressor bound to DNA, preventing transcription, not acting on mRNA.
BIt changes the base sequence of gene R so that the gene no longer codes for a protein. A student who thinks genes are switched off by changing their sequence picks this. The repressor binds to the DNA without changing its sequence; if the repressor leaves, gene R can be transcribed again.
CIt binds to the DNA next to the promoter and blocks RNA polymerase from transcribing gene R.Correct In the model, the repressor sits on its binding site in the DNA, next to the promoter, and RNA polymerase cannot reach the promoter. The repressor is a negative regulatory molecule: by binding to DNA it blocks transcription, so little gene R mRNA is made.
DIt removes gene R from the DNA of the cells that have no need for the protein it codes for. A student who thinks cells lose the genes they do not use picks this. The model shows gene R still present in the DNA; the repressor only blocks its transcription.
In a hypothetical species of plant, leaf cells make large amounts of a protein that binds chlorophyll, but the root cells of the same plant make none of it. Which statement best explains this difference?
Answer and reasoning
AIn root cells, the base sequence of the gene has been changed, and the gene no longer codes for the protein. A student who thinks genes are switched off by changing their sequence picks this. Root cells carry the same, unchanged gene; it is simply not expressed in them.
BBoth cell types carry the gene for the protein, but it is expressed in leaf cells and not in root cells.Correct Leaf and root cells develop from the same zygote and contain the same genes. Gene regulation results in differential gene expression: the gene for the chlorophyll-binding protein is expressed in leaf cells but not in root cells, so only leaf cells make the protein.
CRoot cells have lost the gene for the protein from their DNA because they did not use it. A student who thinks cells lose the genes they do not use picks this. Root cells contain the gene, as all the plant's body cells do; they do not express it.
DRoot cells do not need the protein, so they choose not to make it, unlike the cells of leaves. A student who explains cell processes by need picks this. Cells do not choose; which genes are expressed depends on regulatory molecules, such as the transcription factors present in each cell type.
Certain small RNA molecules regulate gene expression in eukaryotic cells. One such small RNA has a base sequence complementary to part of the mRNA of gene T. Which statement describes how this small RNA can decrease the amount of T protein that is made?
Answer and reasoning
AIt signals that the cell no longer needs T protein, so the cell decides to stop making it. A student who explains cell processes by what the cell needs picks this. The small RNA acts by a mechanism: it base pairs with the complementary part of gene T's mRNA, and the paired mRNA is broken down or not translated; cells do not decide what to make according to need.
BIt changes the base sequence of gene T's DNA, so the gene stops coding for T protein. A student who thinks genes are switched off by changing their DNA sequence picks this. The small RNA base pairs with gene T's mRNA, and regulating a gene does not alter its base sequence.
CIt is translated into a protein, which then binds to the mRNA of gene T and blocks its translation. A student who thinks every RNA is translated into a protein picks this. Small regulatory RNAs act directly as RNA, by base pairing with their target mRNA.
DIt base pairs with gene T's mRNA, which leads to the mRNA being broken down or not translated.Correct Because its sequence is complementary to part of the mRNA of gene T, the small RNA base pairs with that mRNA. The paired mRNA can be broken down or blocked from being translated, so less T protein is made.
In preparation: 0 of 4 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
6.6.A.1 Promoter Fix
Promoter
A DNA sequence at the start of a gene to which RNA polymerase and transcription factors bind to initiate transcription.
Enhancer
A DNA sequence to which transcription factors bind to increase the transcription of a gene; it can lie upstream or downstream of the transcription start site, sometimes far from the gene.
Transcription factor
A protein that binds to a specific DNA sequence, such as a promoter or an enhancer, and affects whether RNA polymerase initiates transcription of a gene.
Upstream and downstream
Positions on DNA relative to the transcription start site: upstream sequences lie on the side away from the direction of transcription, and downstream sequences lie in the direction in which transcription proceeds.
Students often think Promoters and enhancers are proteins that bind to DNA and help RNA polymerase start transcription. In fact No. Promoters and enhancers are DNA sequences. RNA polymerase and transcription factors are proteins that bind to these sequences to initiate transcription.
Students often think Promoters and enhancers are parts of a gene's coding sequence and are translated into the gene's protein. In fact No. Promoters and enhancers are regulatory DNA sequences that affect whether and how much a gene is transcribed; they are not translated into the gene's protein.
6.6.A.2 Negative regulatory molecule Fix
Negative regulatory molecule
A molecule, such as a repressor protein, that inhibits gene expression by binding to DNA and blocking transcription.
Students often think A repressor reduces a gene's expression by breaking down the gene's mRNA after it has been transcribed. In fact No. A repressor is a negative regulatory molecule that binds to DNA and blocks transcription, so less mRNA is made in the first place.
Students often think Genes are switched off by changing their DNA base sequence so that they no longer code for a protein. In fact No. Gene regulation controls whether and how much a gene is expressed, for example by molecules that bind to the gene's DNA or to its mRNA. The gene's base sequence is not changed, so its expression can change again later.
6.6.B.1 Gene regulation Fix
Gene regulation
Control of whether, when and how much a gene is expressed, for example by molecules that bind to DNA and affect transcription.
Differential gene expression
The expression of different sets of genes, at different levels, in different cells of the same organism, although the cells contain essentially the same genes.
Cell specialization
The development of cells with particular structures and functions, which results from the products of the genes that each cell expresses.
Students often think Different cell types contain different genes, because each cell type keeps the genes it uses and loses the others. In fact No. With rare exceptions, the body cells of an organism contain the same genes, inherited from the zygote. Cell types differ in which genes they express and at what levels.
Students often think Every gene in a cell's DNA is expressed, so cells that contain the same genes make the same products. In fact No. Each body cell contains essentially all of the organism's genes but expresses only some of them, and which genes are expressed, and at what levels, differs between cell types.
6.6.B.2 Small regulatory RNA Fix
Small regulatory RNA
A short RNA molecule that regulates gene expression; for example, by base pairing with a complementary sequence in an mRNA, it can cause the mRNA to be broken down or prevent it from being translated.
Students often think Every RNA molecule, including a small regulatory RNA, is translated into a protein that does its job. In fact No. Small regulatory RNAs act as RNA: they base pair with complementary sequences, such as part of an mRNA, and so affect gene expression without being translated.
Students often think The amount of a protein always rises and falls with the amount of its mRNA, because gene expression is controlled only at transcription. In fact No. Gene expression can be regulated after transcription. For example, a small RNA can block translation, so the amount of a protein can fall while the amount of its mRNA stays the same.
5 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 5
In a hypothetical species of fish, transcription of gene L was measured in cells carrying either the intact gene or a copy with one region of nearby DNA deleted. Region A lies 3,000 base pairs upstream of the transcription start site, region B lies immediately upstream of it, and region D lies 2,000 base pairs downstream of the end of the gene. The graph shows mean transcription (n = 6) as a percentage of the intact gene, with error bars of ±2 SE. Which conclusion is supported by the data?
Answer and reasoning
ARegion D affects transcription, as the bars for the intact gene and for D deleted do not overlap.Correct The D-deleted bar runs from 27 to 43 and the intact bar from 92 to 108; the ±2 SE bars are far apart, so deleting region D significantly reduced transcription. A sequence downstream of the gene therefore increases its transcription, as an enhancer can.
BRegion A affects transcription, as the mean for A deleted is lower than the mean for the intact gene. A student who treats any difference between means as real picks this. The A-deleted mean (92) is lower, but its ±2 SE bar (82 to 102) overlaps the intact bar (92 to 108), so a difference has not been shown.
CRegion A is shown to have no effect on transcription, as its bar overlaps that of the intact gene. A student who thinks overlapping error bars prove that two means are equal picks this. Overlap means a difference has not been shown; it does not show that region A has no effect.
DRegion B alone affects transcription, as sequences that control it lie upstream of the gene. A student who thinks regulatory sequences lie upstream of the gene picks this. Deleting region D, downstream of the gene, also reduced transcription significantly: its bar (27 to 43) does not overlap the intact bar.
Working No test statistic is calculated; the decision rests on the ±2 SE error bars. Intact: mean 100, bar 92 to 108. A deleted: mean 92, bar 82 to 102, which overlaps the intact bar (92 to 102 is shared), so a difference has not been shown, though it is not shown to be zero either. B deleted: mean 3, bar 1 to 5, far below 92, so deleting B causes a significant decrease. D deleted: mean 35, bar 27 to 43, which does not overlap 92 to 108, so deleting D causes a significant decrease. Conclusion: region D, downstream of the gene, contains a sequence that increases transcription; region B does too, so B is not the only region that matters.
In a hypothetical species of yeast, protein P represses gene G by binding to a DNA sequence next to the promoter of gene G. A mutation changes this DNA sequence so that protein P can no longer bind to it. Which prediction about cells with this mutation is correct?
Answer and reasoning
AProtein G would have a different amino acid sequence, as gene G has mutated. A student who thinks every mutation near a gene changes its protein picks this. The mutation is in the binding sequence next to the promoter, not in gene G's coding sequence, so it changes how much protein G is made, not its sequence.
BGene G would be transcribed even with protein P present, as P no longer blocks it.Correct Protein P is a negative regulatory molecule: it blocks transcription of gene G by binding to the DNA. If it can no longer bind, nothing blocks RNA polymerase, so gene G is transcribed even in cells where protein P is present.
CGene G would no longer be transcribed, as protein P could not bind to switch it on. A student who thinks every DNA-binding regulator switches genes on picks this. Protein P represses gene G, so preventing its binding increases transcription of gene G.
DThe cells would make extra protein P so that it could still bind and repress gene G. A student who explains cell processes by what the cell needs picks this. Making more protein P would not help, because the binding sequence itself has changed; nothing causes cells to respond in this way.
Researchers tested two cell types from the same individual of a hypothetical species of animal, a muscle cell type (cell type 1) and a skin cell type (cell type 2), for the DNA and the mRNA of three genes. The table shows the results. Which claim is supported by the evidence in the table?
Answer and reasoning
AThe cell types differ in their genes, as each cell type keeps only the genes that it uses. A student who thinks each cell type keeps only the genes it uses picks this. The table shows the DNA of all three genes in both cell types; the cell types differ in which genes they transcribe, not in which genes they have.
BThe cell types express the same genes, as both of them contain the DNA of all three of the genes tested. A student who thinks a cell expresses every gene it contains picks this. Containing a gene is not the same as expressing it: gene X mRNA is absent from cell type 2 and gene Y mRNA from cell type 1.
CThe cell types differ in gene expression, as gene Y is transcribed in skin cells but not muscle cells.Correct Both cell types contain the DNA of all three genes, but gene Y mRNA is found only in cell type 2 (skin) and gene X mRNA only in cell type 1 (muscle). The cells have the same genes but transcribe different ones: differential gene expression.
DThe cell types differ in gene expression, as each cell type chooses the genes it needs. A student who explains cell differences by what each cell needs picks this. The claim about expression is right, but the reason is not evidence from the table, and cells do not choose their genes; regulatory molecules control which genes are expressed.
Researchers think that a small RNA, sRNA-5, reduces the amount of protein K made in cells of a hypothetical species of worm. They add sRNA-5 to one group of cells and measure the amount of protein K. Which treatment of a second group of cells would be the most appropriate control?
Answer and reasoning
AAdd a small RNA of the same length whose bases cannot pair with any part of gene K's mRNA.Correct This control receives the same kind of treatment, a small RNA of the same length added in the same way, but one that cannot pair with gene K's mRNA. If protein K falls only with sRNA-5, the effect can be attributed to sRNA-5's ability to pair with that mRNA, not to adding RNA in general.
BUse cells that lack gene K, so that they cannot make any protein K at all. A student who thinks the control for a regulator is a group without the gene it regulates picks this. These cells make no protein K whatever the treatment, so they cannot show whether sRNA-5 reduces it.
CAdd sRNA-5 to the second group as well, and measure protein K in the same way. A student who thinks a repeat of the treatment is a control picks this. A second group given sRNA-5 is a replicate; it shows how much results vary, not what sRNA-5 does.
DUse cells of a different worm species that make protein K, and add no sRNA-5. A student who thinks a control can differ in more than one way picks this. These cells differ in species as well as in lacking sRNA-5, so a difference in protein K could be caused by either.
A small RNA complementary to part of the mRNA of gene T was added to cells of a hypothetical species of fly at time 0. The graph shows the amounts of gene T mRNA and of T protein in the cells over the next 48 hours, each as a percentage of its amount at 0 hours. Which statement describes the data?
Answer and reasoning
AT mRNA and T protein both fell over the 48 hours, at roughly the same rate as each other. A student who expects protein amounts to follow mRNA amounts picks this. Only the protein fell; the mRNA stayed between 97% and 101%.
BT mRNA was neither made nor broken down in the cells, as its line stays flat for 48 hours. A student who thinks a constant amount means nothing is happening picks this. A flat line shows that the amount of T mRNA did not change overall; the graph does not show whether it was being made and broken down at equal rates.
CThe small RNA lowered T mRNA too, as the mRNA was lower at 36 hours than at the start. A student who treats any difference between two values as a real effect picks this. The mRNA values, 97% to 101%, go up and down by a few percent with no trend; 97% at 36 hours is not evidence of a decrease.
DBy 48 hours T protein had fallen to about a quarter of its starting amount, while T mRNA stayed level.Correct The T protein line falls from 100% to 26% over 48 hours, about a quarter of the starting amount, while the T mRNA line stays between 97% and 101%. The small RNA reduced the amount of T protein without reducing the amount of T mRNA, consistent with blocking translation.
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
