Chap 18 For Bio Final

Which statement(s) about repressible operons is/are correct? -

-A repressible operon is on unless a corepressor is present. -Repressible operons usually contain genes that code for anabolic enzymes. [A repressible operon is usually on but can be turned off when a corepressor interacts with and activates the repressor. The enzymes in an inducible operon generally function in anabolic pathways. Read about repressible operons.]

PART B - Regulation of transcription initiation The diagram below shows two stretches of DNA in the genome of an imaginary eukaryotic cell. The top stretch of DNA includes the fantasin gene, along with its promoter and one of its enhancers. The bottom stretch of DNA includes the imaginin gene, its promoter, and one of its enhancers. The slash marks (//) indicate that more than 1,000 nucleotides separate the promoter and enhancer of each gene. Which statements about the regulation of transcription initiation in these genes are true? Select all that apply. -

-Control elements C, D, and E are distal control elements for the imaginin gene. -The fantasin gene will be transcribed at a high level when activators specific for control elements A, B, and C are present in the cell. -Both the fantasin gene and the imaginin gene will be transcribed at high levels when activators specific for control elements A, B, C, D, and E are present in the cell. [Only certain genes are transcribed in a eukaryotic cell at any particular time. The regulation of transcription initiation depends on the interaction of specific transcription factors with specific control elements in enhancers. In the imaginary eukaryotic cell used as an example here, the enhancers for the fantasin gene and imaginin gene are unique because they contain different sets of control elements (A, B, and C for the fantasin gene; C, D, and E for the imaginin gene). Each gene will be transcribed at a high level when activators specific for all of the control elements in its enhancer are present in the cell.]

How are genes coordinately controlled in eukaryotic cells? -

-Coordinately controlled genes in eukaryotic cells are activated by the same chemical signals. -Coordinately controlled genes in eukaryotic cells share a set of control elements. [In eukaryotes, specific transcription factors bind to control elements, promoting transcription of coordinately controlled genes, even if the genes are on separate chromosomes. Read about coordinately controlled genes in eukaryotes.]

Which statement(s) about inducible operons is/are correct? -

-In an inducible operon, an inducer inactivates the repressor. -In an inducible operon, the repressor is synthesized in an active form. [An inducible operon is usually off but can be turned on when an inducer interacts with and inactivates the repressor. The enzymes in an inducible operon generally function in catabolic pathways. Read about inducible operons.]

Which noncoding RNAs are correctly matched with their function? -

-Piwi-associated RNAs (piRNAs) reestablish appropriate methylation patterns in the genome during gamete formation. -Small interfering RNAs (siRNAs) bind to complementary sequences in mRNA and block its translation. -MicroRNAs (miRNAs) bind to complementary sequences in mRNA and block its translation. [Read about the multiple roles of noncoding RNAs.]

PART A - Modification of chromatin structure Which statements about the modification of chromatin structure in eukaryotes are true? Select all that apply. -

-Some forms of chromatin modification can be passed on to future generations of cells. -Acetylation of histone tails in chromatin allows access to DNA for transcription. -DNA is not transcribed when chromatin is packaged tightly in a condensed form. -Acetylation of histone tails is a reversible process. -Methylation of histone tails in chromatin can promote condensation of the chromatin. [One of the mechanisms by which eukaryotes regulate gene expression is through modifications to chromatin structure. When chromatin is condensed, DNA is not accessible for transcription. Acetylation of histone tails reduces the attraction between neighboring nucleosomes, causing chromatin to assume a looser structure and allowing access to the DNA for transcription. If the histone tails undergo deacetylation, chromatin can recondense, once again making DNA inaccessible for transcription. Recent evidence suggests that methylation of histone tails can promote either the condensation or the decondensation of chromatin, depending on where the methyl groups are located on the histones. Thus, methylation can either inactivate or activate transcription, and demethylation can reverse the effect of methylation. Changes in chromatin structure may be passed on to future generations of cells in a type of inheritance called epigenetic inheritance.]

PART A - Operon vocabulary Can you match terms related to operons to their definitions? Drag the terms on the left to the appropriate blanks on the right to complete the sentences. -

1. A(n) OPERON is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway. 2. The GENES OF AN OPERON is/are arranged sequentially after the promoter. 3. A(n) PROMOTOR is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place. 4. A(n) REGULATORY GENE codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes. 5. Regulatory proteins bind to the OPERATOR to control expression of the operon. 6. A(n) REPRESSOR is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter. 7. A(n) INDUCER is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on. [An operon is made up of a promoter and the genes of the operon. The promoter, which includes an operator, is the stretch of DNA where RNA polymerase binds. Regulatory proteins bind to the operator. The genes of the operon code for a related set of proteins. A regulatory gene located away from the operon codes for a protein that controls the operon.]

PART C Which of these indicates an enhancer region? -

A [This is an enhancer region.]

PART A _____ bind(s) to DNA enhancer regions. -

Activators [Activators are a type of transcription factor that bind to enhancer regions.]

PART B Which of the following regulatory elements is not composed of DNA sequences? -

Activators [Activators are proteins that are involved in transcription initiation.]

PART G Which of the following enzymes converts ATP to cAMP? -

Adenylyl cyclase [Adenylyl cyclase converts ATP to cAMP, which helps CAP bind and facilitates binding of RNA polymerase to the lac promoter.]

PART D - Interpreting the graph Do the data suggest that any of these possible control elements are actual control elements? -

All three appear to be control elements. [All three elements appear to be control elements because when they were deleted, the levels of reporter mRNA differed from the level produced by the intact enhancer construct. For each of the three treatment groups, look at how the level of reporter mRNA changes relative to the intact enhancer construct (top). What do those differences indicate?]

PART A Which of the following statements best defines the term operon? -

An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter. [This arrangement of genes is common in bacteria. For example, genes involved in lactose metabolism are clustered in the lac operon of E. coli, and genes involved in tryptophan metabolism are in the trp operon.]

18.4.3: Why are fruit fly maternal effect genes also called egg-polarity genes?

Because their products, made by the mother, determine the heads and tails end, as well as the back and belly, of the egg

18.1.3: Describe binding of RNA polymerase, repressors, and activators to the lac operon when both lactose and glucose are scarce. What would be the effect on transcription? How might the transcription of other genes outside the lac operon be regulated if another sugar were present?

Because there is little glucose, cAMP would be bound to CAP which would be bound to the promoter, favoring the binding of RNA polymerase. However, in the absence of lactose, the repressor would be bound to the operator, blocking RNA polymerase binding to the promoter. The operon genes would therefore not be transcribed. If another sugar were present and the genes encoding enzymes for its breakdown were in an operon regulated like the lac operon, we might expect to find the transcription of those genes

18.1.1: How does binding of the trp corepressor and the lac inducer to their respective repressor proteins alter repressor function and transcription in each case?

Binding by the trp corepressor (tryptophan) activates the trp repressor, shutting off transcription of the trp operon; binding by the lac inducer (allolactose) inactivates the lac repressor, leading to transcription of the lac operon.

18.3.1: Compare and contrast miRNA and siRNAs

Both are small, single-stranded RNAs that associate with a complex of proteins and then can base-pair with mRNAs that have a complementary sequence. This leads to either degradation of the mRNA or the blockage of its translation. Both are processed from double-stranded RNA precursors by the enzyme Dicer. However, miRNAs are encoded by genes in teh cell's genome, and the single transcript folds back on itself to form one or more double-stranded hairpins, each of which is processed into miRNA. In contrast, siRNAs arise from a longer stretch of double-stranded RNA, which may be introduced into the cell by a virus or an experimenter.

18.4.2: The signal molecules released by an embryonic cell can induce changes in a neighboring cell without entering the cell. How?

By binding to a receptor on the receiving cell's surface, and triggering a signal transduction pathway that affects genes expression

PART D Which of these directly bind(s) to the promoter? -

C and D [Both RNA polymerase and transcription factors bind with the promoter.]

18.4.1: As you learned in Chapter 12, mitosis gives rise to two daughter cells that are genetically identical to the parent cell. Yet, you, the product of many mitotic divisions, are not composed of identical cells. Why?

Cells undergo differentiation during embryonic development, becoming different form each other; in the adult organism, there are many highly specialized cell types

18.2.4: Once mRNA encoding a particular protein reaches the cytoplasm, what are four mechanisms that can regulate the amount of the protein that is active in the cell?

Degradation of the mRNA, regulation of translation, activation of the protein, and protein degredation

PART G Did deletion of any of the possible control elements cause an increase in reporter gene expression? How can you tell? -

Deletion of control element #1 or #2 caused an increase in reporter gene expression; both constructs resulted in over 100% of the control level of mRNA. [For cells incubated with the DNA constructs in which element #1 or #2 was deleted, the amount of reporter mRNA made was over 100% of the amount of reporter mRNA made by the cells in the control group. This result indicates that the deletion of control element #1 or #2 causes an increase in reporter gene expression.]

PART E Did deletion of any of the possible control elements cause a reduction in reporter gene expression? How can you tell? -

Deletion of element #3 caused a reduction in reporter gene expression; that construct resulted in less than 50% of the control level of mRNA. [For cells incubated with the DNA construct in which element #3 was deleted, the amount of reporter mRNA made was less than 50% of the amount of reporter mRNA made by the cells in the control group. This result indicates that the deletion of control element #3 causes a reduction in reporter gene expression.]

PART D Which of the following regulatory DNA sequences might be located thousands of nucleotides away from the transcription start site of a gene? -

Enhancer [Enhancers can function thousands of nucleotides away from the promoter and transcription start site. This sequence is located within the promoter region of the gene, just upstream of the transcription start site.]

18.2.5: Examine the figure and suggest a mechanism by which the yellow activator protein comes to be present in the liver cell but not in the lens cell.

Expression of the gene encoding the yellow activator must be regulated at one of the steps shown in the figure. The YA gene might be transcribed only in liver cells because the necessary activators for the enhancer of the YA gene are found only in liver cells

PART C True or false? Regulatory and basal transcription factors regulate transcription by binding to the promoter. -

False [Basal transcription factors do indeed bind to the promoter, but regulatory transcription factors bind to promoter-proximal elements and enhancers.]

PART F True or false? One possible way to alter chromatin structure such that genes could be transcribed would be to make histone proteins more positively charged. -

False [The positive charge on histone proteins allows them to interact tightly with negatively charged DNA, thus inhibiting transcription. To disrupt this interaction, the histone proteins would have to be made more negatively charged.]

PART H True or false? The mechanism by which glucose inhibits expression of the lac structural genes is known as catabolite stimulation, whereas the mechanism by which lactose stimulates expression of the lac structural genes is known as allosteric regulation. -

False [The process by which lactose binds to the lac repressor and inactivates it by causing it to change shape is known as allosteric regulation. However, the process by which glucose causes cAMP levels in the cell to drop, thereby preventing CAP from stimulating expression of the lac structural genes, is known as catabolite repression.]

18.2.2: Compare the roles of general and specific transcription factors in regulating gene expression

General transcription factors function in assembling the transcription initiation complex at the promoter for all genes. Specific transcription factors bind to control elements associated with a particular gene and, once bound, either increase (activators) or decrease (repressors) transcription of that gene

18.2.1: In general, what is the effect of histone acetylation and DNA methylation on gene expression?

Histone acetylation is generally associated with gene expression, while DNA methylation is generally associated with lack of expression

PART C What is allosteric regulation? -

In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity. [Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators. First, genes that are expressed constitutively are not regulated—they are transcribed all the time. Second, allosteric regulation relates to more than the phenomenon of gene expression.]

PART D Under which conditions are the lac structural genes expressed most efficiently? -

No glucose, high lactose [When glucose is absent and lactose levels are high, the lac structural genes are expressed the most efficiently. Without glucose, cAMP is produced and CAP can stimulate transcription of the structural genes. In the presence of lactose, the repressor does not bind to the operator and therefore does not block transcription.]

PART A Which of the following terms describes the DNA-protein complexes that look like beads on a string? -

Nucleosome [The "beads on a string" appearance of nucleosomes comes from the wrapping of DNA around a core of eight histone proteins.]

Promoters -

Promoters are DNA sequences.

PART B What molecule binds to promoters in bacteria and transcribes the coding regions of the genes? -

RNA polymerase [RNA polymerase is the enzyme that binds to promoters and transcribes the coding regions of genes into RNA.]

PART E Which of the following events in transcription initiation likely occurs last? -

RNA polymerase binds to the promoter of the gene. [RNA polymerase is recruited only when other transcription factors, including TBP, are assembled at the promoter.]

It is possible for a cell to make proteins that last for months; hemoglobin in red blood cells is a good example. However, many proteins are not this long-lasting; they may be degraded in days, hours, or even minutes. What is the advantage of short-lived proteins? -

Short-lived proteins enable the cells to control their activities precisely and efficiently. [Some proteins are needed only for short-term use.]

18.1.2: A certain mutation in E. coli changes the lac operator so that the active repressor cannot bind. How would this affect the cell's reproduction of B-galatctosidase?

The cell would continuously produce B-galaactosidase and the two other enzymes for lactose utilization, even in the absence of lactose, thus wasting cell resources.

18.3.2: Imagine that the mRNA being degraded in the figure codes for a protein that promotes cell division in a multicellular organism. What would happen, both in the cell and to the organism, if a mutation disabled the gene encoding the miRNA that triggers his degradation?

The mRNA would persist and be translated into the cell division-promoting protein, and the cell would probably divide. If the intact miRNA is necessary for inhibition of cell division, then division of this cell might be inappropriate. Uncontrolled cell division could lead to the formation of a tumor.

18.2.3: Suppose you compared the nucleotide sequences of the distal control elements in the enhancers of three genes that are expressed only in muscle tissue. What would you expect to find and why?

The three genes should have some similar or identical sequences in the control elements of their enhancers. Because of this similarity, the same specific transcription factors could bind to the enhancers of all three genes and stimulate their expression coordinately

PART E What happens to the expression of the lacI gene if lactose is not available in the cell? -

There is no change—the lacI gene is constitutively expressed. [The lacI gene is expressed regardless of the presence of lactose. Only the structural genes of the lac operon are affected by the presence or absence of lactose.]

PART F What is the function of the lacZ gene? -

This gene encodes an enzyme, b-galactosidase, which cleaves lactose into glucose and galactose. [The lacZ gene encodes b-galactosidase, a key enzyme in lactose metabolism. When lactose is present in the cell, the cell expresses lacZ and metabolizes lactose.]

A gene on human chromosome 15 is expressed throughout the body. However, in the brain, only the maternal copy of the gene is expressed, whereas the paternal copy of the gene is silent and not transcribed. What accounts for this pattern of expression this gene displays in the brain? -

Through genomic imprinting, methylation regulates expression of the paternal copy of the gene in the brain. [Imprinting of the paternal copy of the gene by DNA methylation inactivates it and prevents its expression in brain cells. Read about DNA methylation and genomic imprinting.]

PART F If deletion of a control element causes a reduction in gene expression, what must be the normal role of that control element? -

To activate gene expression; without the control element, activators are not able to bind to the enhancer, and the level of gene expression decreases. [If a repressor cannot bind, wouldn't you expect the expression to increase instead of decrease?]

PART H If deletion of a control element causes an increase in gene expression, what must be the normal role of that control element? -

To repress gene expression; without the control element, repressors are not able to bind to the enhancer, and the level of gene expression increases.

Why is the lac operon said to be an inducible operon? -

When allolactose is present, it induces the inactivation of the lac repressor. [The lac repressor keeps the production of lactose-digesting enzymes turned off. When allolactose is present, the lac repressor is inactivated, allowing the expression of lactose-digesting enzymes.]

PART C - Alternative RNA splicing The diagram below shows a segment of DNA containing an imaginary gene (Z) and the primary RNA transcript that results from the transcription of gene Z. Exons are represented in green and introns are represented in blue. The figure shows a segment of DNA containing an imaginary gene Z and the primary RNA transcript that results from the transcription of gene Z. Exons are represented in green and introns are represented in blue. They are labeled with letters as well. So, the exons are A, C, E, G, and I. Introns are B, D, F, and H. Both DNA and primary RNA transcript contain all the mentioned exons and introns. Which of the following choices represent mRNA molecules that could be produced from the primary RNA transcript by alternative RNA splicing? (In each choice, the yellow part on the left represents the 5' cap, and the yellow part on the right represents the poly-A tail.) Select all that apply. -

[Alternative RNA splicing produces different mRNA molecules from the same primary RNA transcript. During alternative RNA splicing, all introns are removed, and some exons may also be removed. The removal of different exons produces different mRNA molecules, which are then translated into different proteins. Alternative RNA splicing can greatly expand the number of proteins produced from the same gene.]

PART C - Regulation of a hypothetical operon You are studying a bacterium that utilizes a sugar called athelose. This sugar can be used as an energy source when necessary. Metabolism of athelose is controlled by the ath operon. The genes of the ath operon code for the enzymes necessary to use athelose as an energy source. You have found the following: -The genes of the ath operon are expressed only when the concentration of athelose in the bacterium is high. -When glucose is absent, the bacterium needs to metabolize athelose as an energy source as much as possible. -The same catabolite activator protein (CAP) involved with the lac operon interacts with the ath operon. Based on this information, how is the ath operon most likely controlled? Drag the labels onto the diagram to identify the small molecules and the states of the regulatory proteins. Not all labels will be used. -

[Metabolism of the sugar athelose in this hypothetical system is controlled by an operon that exhibits both positive control and negative control. Transcription of the ath operon is turned on when athelose is present (negative control), and sped up when the bacterium runs out of glucose and must rely on athelose for energy (positive control).]

explain how the types of mutations that lead to cancer are different for a proto-oncogene and a tumor-suppressor gene, in terms of the effect of the mutation on the activity of the gene product. -

a cancer causing mutation in a proto-oncogene usually makes the gene product overactive, whereas a cancer causing mutation in a tumor suppressor gene usually makes the gene product nonfunctional.

compare and contrast the roles of the corepressor and the inducer in negative regulation of an operon. -

a corepressor and an inducer are both small molecules that bind to the repressor protein in an operon, causing the repressor to change shape. in the case of a corepressor (like tryptophan) this shape change allows the repressor to bind to the operator, blocking transcription. in contrast, an inducer causes the repressor to dissociate from the operator, allowing transcription to begin.

muscle cells differ from nerve cells mainly because they: a. express different genes b. contain different genes c. use different genetic codes d. have unique ribosomes e. have different chromosomes -

a. express different genes

cell differentiation always involves: a. the production of tissue-specific proteins, such as muscle actin b. the movement of cells c. the transcription of the myoD gene d. the selective loss of certains genes from the genome e. the cell's sensitivity to environmental cues, such as light or heat -

a. the production of tissue-specific proteins, such as muscle actin

the p53 protein can activate genes involved in apoptosis. discuss how mutations in genes coding for proteins that function in apoptosis could contribute to cancer. -

apoptosis is signaled by p53 protein when a cell has a lot of DNA damage, so apoptosis plays a protective role in eliminating a cell that might contribute to cancer. if mutations in the genes in the apoptotic pathway blocked apoptosis, a cell with such damage could continue to divide and might lead to tumor formation.

proto-oncogenes can change into oncogenes that cause cancer. which of the following best explains the presence of these potential time bombs in eukaryotic cells? a. proto-oncogenes first arose from viral infections b. proto-oncogenes normally help regulate cell division c. proto-oncogenes are genetic "junk" d. proto-oncogenes are mutant versions of normal genes e. cells produce proto-oncogenes as they age -

b. proto-oncogenes normally help regulate cell division

within a cell, the amount of protein made using a given mRNA molecule depends partly on: a. the degree of DNA methylation b. the rate at which the mRNA is degraded c. the presence of certain transcription factors d. the number of introns present in the mRNA e. the types of ribosomes present in the cytoplasm -

b. the rate at which the mRNA is degraded

PART B What is the event that IMMEDIATELY follows the last event of this animation? To view the animation, click here. Then click on the image to start the animation. -

binding of RNA polymerase to the promoter [The bending of the DNA allows for the interaction of transcription factors and RNA polymerase.]

how does the binding of the trp corepressor and the lac inducer to their respective repressor proteins alter repressor function and transcription in each case? -

binding the trp corepressor (tryptophan) activates the trp repressor, shutting off transcription of the trp operon; binding by the lac inducer (allolactose) inactivates the lac repressor, leading to transcription of the lac operon.

miRNAs can control gene expression by what action? -

binding to mRNAs and degrading them or blocking their translation [miRNAs can effectively "silence" genes by binding to mRNA transcripts. The mRNAs are either broken down by enzymes or are unable to physically interact with the ribosomes to complete translation.]

which of the following is an ex of post-transcriptional control of gene expression: a. the addition of methyl groups to cytosine bases of DNA b. the binding of transcription factors to a promoter c. the removal of introns and alternative splicing of exons d. gene amplification contributing to cancer e. the folding of DNA to form heterochromatin -

c. the removal of introns and alternative splicing of exons

what would occur if the repressor of an inducible operon were mutated so it could not bind the operator? a. irreverisble binding of the repressor to the promoter b. reduced transcription of the operon's genes c. building of a substrate for the pathway controlled by the operon d. continuous transcription of the operon's genes e. overproduction of catabolite activator protein (CAP) -

d. continuous transcription of the operon's genes

if a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then: a. the amino acid inactivates the repressor b. the enzymes produced are called inducible enzymes c. the repressor is active in the absence of the amino acid d. the amino acid acts as a corepressor -

d. the amino acid acts as a corepressor

which of the following statements about the DNA in one of your brain cells is true: a. most of the DNA codes for protein b. the majority of genes are likely to be transcribed c. each gene lies immediately adjacent to an enhancer d. many genes are grouped into operon like clusters e. it is the same as the DNA in one of your heart cells -

e. it is the same as the DNA in one of your heart cells

In humans, the hormone testosterone enters cells and binds to specific proteins, which in turn bind to specific sites on the cells' DNA. These proteins probably act to do what? -

help RNA polymerase transcribe certain genes [Testosterone stimulates the expression of genes involved in male sexual characteristics; it follows that the proteins that it interacts with and which bind to DNA will promote transcription.]

what is the effect of histone acetylation and DNA methylation on gene expression? -

histone acetylation is generally associated with gene expression, while DNA methylation is generally associated with lack of expression.

DNA methylation is a mechanism used by eukaryotes to do what? -

inactivate genes [DNA methylation, involving the attachment of methyl groups to certain bases, is a mechanism for the long-term inactivation of genes during development.]

PART B - Regulation of model operons The trp and lac operons are regulated in various ways. How do bacteria regulate transcription of these operons? Sort the statements into the appropriate bins depending on whether or not each operon would be transcribed under the stated conditions. -

operon is not transcribed -trp operon: tryptophan present -lac operon: lactose absent operon is transcribed, but not sped up through positive control -lac operon: lactose present, glucose present -trp operon: tryptophan absent operon is transcribed quickly through positive control -lac operon: lactose present, glucose absent [The trp operon is regulated through negative control only. When tryptophan is present, the operon genes are not transcribed. The lac operon is regulated through both negative control and positive control. Negative control: -When lactose is absent, the repressor protein is active, and transcription is turned off. -When lactose is present, the repressor protein is inactivated, and transcription is turned on. Positive control: -When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rate of transcription if lactose is present.]

a certain mutation in e. coli changes the lac operator so that the active repressor cannot bind. how would this affect the cell's production of B-galactosidase? -

the cell would continuously produce b-galactosidase and the 2 other enzymes for lactose utilization, even in the absence of lactose, thus wasting cell resources.

PART C What was the control treatment in this experiment? -

the construct that had no DNA deleted from the enhancer [The control treatment was the construct that had no DNA deleted from the enhancer. All the other treatment groups were compared to that control group.]

18.4.4: In a blownup box in the figure, the lower cell is synthesizing signal molecules, whereas the upper cell is expressing signal receptors. In terms of gene regulation, explain how these cells came to have different functions.

the lower cell is making signal molecules because the gene encoding them is activated, meaning that the appropriate specific transcription factors are binding to the gene's enhancer. The genes encoding are also being expressed in this cell because the transcriptional activators that can turn the on were expressed inthe precursor to this cell. These cytoplasmic determinants were distributed unevenly to daughter cells, resulting in cells going different developmental pathways

PART A - Understanding the experimental design The diagrams show the intact DNA sequence (top) and the three experimental DNA sequences. A red X indicates the possible control element (1, 2, or 3) that was deleted in each experimental DNA sequence. The area between the slashes represents the approximately 8 kilobases of DNA located between the promoter and the enhancer region. The horizontal bar graph shows the amount of reporter gene mRNA that was present in each cell culture after 48 hours relative to the amount that was in the culture containing the intact enhancer region (top bar = 100%). What was the independent variable in this experiment? -

the possible control element that was deleted [The independent variable was the possible control element that was deleted from the experimental sequences because the researchers manipulated that variable in each treatment.]

compare the usual functions of proteins encoded by proto-oncogenes with the functions of proteins encoded by tumor-supressor genes. -

the protein product of a proto-oncogene is usually involved in a pathway that stimulates cell division. the protein product of a tumor suppressor gene is usually involved in a pathway that inhibits cell division.

PART B What was the dependent variable in this experiment? -

the relative level of reporter gene mRNA [The dependent variable was the relative level of reporter gene mRNA because that was the response that was measured in the experiment.]

under what circumstances is cancer considered to have a hereditary component? -

when an individuals has inherited an oncogene or a mutant allele of a tumor-suppressor gene.

describe the binding of RNA polymerase, repressors, and activators of the lac operon when both lactose and glucose are scarce. what is the effect of these scarcities on transcription of the lac operon? -

when glucose is scarce, cAMP is bound to CAP and CAP is bound to the promoter, favoring the binding of RNA polymerase. however, in the absence of lactose, the repressor is bound to the operator, blocking RNA polymerase binding to the promoter.