Lifesci 7A final practice exam questions

Which strand is bound to more RNA primers to the left of the dotted line?

top strand

Assume you are trying to insert a gene into a plasmid. Someone gives you a preparation of genomic DNA that has been cut with restriction enzyme X. The gene you wish to insert has sites on both ends for cutting by restriction enzyme Y. You have a plasmid with a single site for Y but not for X. Your strategy should be to:

cut the DNA again with restriction enzyme Y and insert these fragments into the plasmid cut with restriction enzyme Y

Which molecule would most likely require a transport protein to cross the plasma membrane of a red blood cell? a. CO2 b. H2O c. O2 d. C6H12O6

d. C6H12O6; Larger, more polar molecules are less able to cross a membrane than smaller, nonpolar molecules.

A mutant strain of E. coli is found that produces both β-galactosidase and permease constitutively. Which of the following genotypes could cause this?

lacI- and lacOc

Which of the answer choices could be true if a plant cell is exposed to a toxin that makes the thylakoid membrane freely permeable to protons? Select all that apply.

The amount of NADPH in the chloroplast would increase and there would be no ATP available to drive carbohydrate synthesis in the Calvin cycle.

What would happen to the daughter cells if the G2 phase of the parent cell is shortened?

The cells would be smaller than normal. During G2 phase, synthesis of the macromolecules and cellular structures occurs to provide sufficient supply for the two daughter cells formed after mitosis.

Can it be determined from the data in the table which eukaryotic species has the largest genome? Can it be determined which species has the greatest number of chromosomes?

no; no The size of the genome, the number of genes, and the number of chromosomes are not correlated, a phenomenon known as the C-value paradox.

A gene that normally has the sequence CAGAGCCTATTAGGC is replicated as CAGAGCTGACGAGGC. Which of the repair mechanisms would most likely be employed to fix this replication error?

nucleotide excision repair

Which of the options is circled in this electron micrograph?

one double-stranded DNA molecule

Each DNA parent strand within a replication bubble acts as a template strand that produces:

one leading strand and one lagging strand.

As a piece of linear DNA is replicated, the leading strand will have _____ RNA primer(s) and the lagging strand will have _____ RNA primer(s).

one; many

Colchicine is a drug that blocks the assembly of microtubules. If dividing cells are treated with colchicine, at what stage of mitosis would you predict the arrest would occur?

prophase Alignment of the chromosomes along the metaphase plate requires the attachment of spindle fibers, which are microtubules. If they fail to assemble, the cell will never arrange chromosomes in a way characteristic of metaphase.

If a mutation rendered the signal recognition particle nonfunctional, what would be the most obvious effect on the cell?

All proteins normally secreted by the cell would remain in the cytosol.

Consider the haplotype for the bacterial lac operon: I-O+Z+. There is also a plasmid with the haplotype: I+OcZ-. For all of the questions below, assume there is no glucose and no inducer. Functional beta-galactosidase will be produced in this cell:

False

Exiting early from G2 would cause the mutant cells to look this way:

False

FeS1 would accumulate in its reduced state:

False

Gel set C could result from a mutation that causes methylation of the CpG bases in the promoter region of the gene, assuming that WT is not methylated:

False

Hemoglobin would be synthesized by a ribosome on the rough ER:

False

Individual alpha-helices found in hemoglobin are stabilized by ionic bonds:

False

One of the primers failed to bind the cDNA template:

False

Changing nucleotide 5 from A to G would result in a missense mutation:

False

Repressor protein will be bound to both operators in this cell:

False

T/F ATP synthase will catalyze its reaction more quickly.

False

T/F Molecule X could form a hydrogen bond with another Molecule X

False

T/F Molecule X could form an ionic bond with Cl-

False

T/F The Calvin Cycle will proceed normally.

False

Examine the figure shown, which depicts one stage in the process of translation in a eukaryote. What will happen when the ribosome shifts one codon further on the mRNA, assuming the next codon is not a stop codon? Select all that apply.

- A new tRNA will bind to the ribosome. - The tRNA carrying the polypeptide will be in the P site. - The tRNA that is no longer carrying the polypeptide will be ejected from the ribosome.

Suppose you know the sequence of a region of DNA in an organism, but you want to know the unknown sequences that flank this known sequence. Cleverly, you cleave the DNA with a restriction enzyme at restriction sites outside the known sequence and then use DNA ligase to form a circle as shown in the figure. The dark blue portion of the circles represents double-stranded DNA whose sequence is known, and the light blue portion represents the flanking regions with unknown sequences. The numbered arrows are places where you consider designing PCR primers, with the 3' end of each primer indicated by the arrowhead. Which primers would you use to amplify the light blue region of the circle?

1 and 3 There are three important things to remember: 1) DNA polymerase can add nucleotides only to 3' end of the primer. 2) The 3' ends of both primers should be pointing to each other in order to amplify the region between them. 3) Sequences of the primers should be complementary and antiparallel to the template strands. Only the pair of primers 1 and 3 fulfil these requirements.

Imagine you are following a particular tRNA, called tRNAQ, through the process of translation in a eukaryote. In what order does tRNAQ go through the steps listed? Note that some steps may be used more than once. - The polypeptide is transferred to tRNAQ. - tRNAQ binds the A site of the ribosome. - tRNAQ binds the P site of the ribosome. - The ribosome shifts, with tRNAQ still bound. - tRNAQ binds the E site of the ribosome.

1. tRNAQ binds the A site of the ribosome. 2. The polypeptide is transferred to tRNAQ. 3. The ribosome shifts, with tRNAQ still bound. 4. tRNAQ binds the P site of the ribosome. 5. The ribosome shifts, with tRNAQ still bound. 6. tRNAQ binds the E site of the ribosome.

The oligonucleotide primers used in the polymerase chain reaction are typically 20-30 nucleotides in length or longer; however, for purposes of this problem, assume that six nucleotides is long enough. You wish to amplify the fragment shown (the raised dots indicate several kilobases of DNA sequence not shown) and decide to design primers corresponding to the regions that are shown in bold. What primer sequences would you use?

5'-ACTTGC-3' and 5'-TGCCAC-3' There are three important things to remember: 1) DNA polymerase can add nucleotides only to 3' end of the primer. 2) The 3' ends of both primers should be pointing to each other in order to amplify the region between them. 3) Sequences of the primers should be complementary and antiparallel to one of the strands that are underlined. Only pair of primers 5'-ACTTGC-3' and 5'-TGCCAC-3' fulfill these requirements.

A certain restriction enzyme X cleaves double-stranded DNA at the sequence shown, where the slash indicates where each strand is cleaved. 5'-AA/ATTT-3'3'-TTTA/AA-5' Note that the cleavage results in a two-base pair single-stranded region at the 5' end that allows the cleaved ends to undergo base pairing. Which of the restriction enzymes that cleave double-stranded DNA (indicated by the slash) would produce overhanging ends able to pair with those produced by enzyme X?

5'-GG/ATCC-3 '3'-CCTA/GG-5' First of all, the overhanging ends should be 3' ends because the strands are antiparallel. This means that answer option B (5'-AATA/TT-3' 3'-TT/ATAA-5') and answer option E (5'-GGAT/CC-3' 3'-CCTA/GG-5') are wrong—these restriction enzymes produce 5' overhangs. Answer option C (5'-AAA/TTT-3' 3'-TTT/AAA-5') and answer option D (5'-GGA/TCC-3' 3'-CCT/AGG-5') are also wrong because these enzymes produce blunt ends. The correct answer is option A (5'-GG/ATCC-3' 3'-CCTA/GG-5').

A double-stranded DNA molecule, only part of which is shown, is being transcribed. If the molecule is transcribed from left to right, one of the nucleotides shown in bold would be the first transcribed in this small molecule. 5′—ATGATCGGATCGATCCAT—3′ 3′—TACTAGCCTAGCTAGGTA—5′ Which sequence is the correct mRNA produced from the transcription of this DNA molecule?

5′-AUGAUCGGAUCGAUCCAU-3′ (RNA polymerase can synthesize RNA only in 5′ to 3′ direction. Hence, the template DNA strand is the lower one, in the 3′ to 5′ direction. RNA complementary to this strand is 5′-AUGAUCGGAUCGAUCCAU-3′.)

The product of this gene contains how many amino acids?

6

How many hydrogen atoms are present in a hydrocarbon chain of five carbon atoms with two double bonds and two single bonds?

8

Three carbon atoms are linked by single covalent bond such that those carbon atoms and bonds together form the shape of a V. All of the unshared electrons form covalent bonds with hydrogen. How many hydrogen atoms does this molecule contain?

8

Gel pair that could result from a missense mutation in exon 3:

A

Gel pair that could result from the insertion of 20 bases in exon 2:

B

You would like to ligate a fragment you cleaved with the restriction enzyme BamHI into a plasmid you cleaved with a different enzyme. Which of these enzymes' overhangs will be compatible with BamHI-generated fragments? BamHI sequence and cleavage site: 5' G^GATCC 3' (^ indicates cut site)

BclI 5' T^GATCA 3'

Muscle cells in the mammalian heart are multinucleate, meaning that multiple nuclei are present in the cytoplasm of individual large cells. Predict what is different about the cell cycle in a muscle cell.

Cytokinesis does not occur. Muscle cells are multinucleate because they perform DNA synthesis in S phase and mitosis to form two nuclei, but cytokinesis is blocked, so the cells accumulate the divided nuclei.

The diagram below shows a gene with four exons. The reading frame that encodes the protein is shaded and begins in exon 1 and ends in exon 3. Each of the questions below describes a different mutation. Determine which pair of mRNA and protein gels (A-E) you would most likely observe as a consequence of the mutation. On each gel, "Non" is the nonmutant version of the mRNA/protein and "Mut" is the mutated version of the mRNA/protein. Gel pair that could result from a nonsense mutation in exon 2:

D

Which of the statements most accurately describes the benefits of the proofreading function of DNA polymerase?

DNA polymerase can repair most mutations as they occur during DNA replication.

One difference between eukaryotic and prokaryotic DNA packaging is:

DNA wraps around histones in eukaryotic packaging.

Compared to when the Na+ channel is closed, how will the transport of Waste molecules change when the Na+ channel is open? The rate of Waste transport out of the cell will:

Decrease

The concentration of ADP in a cell is increasing. Assuming that the cell has plenty of glucose and oxygen available, carbon dioxide (CO2) production by the cell should:

Decrease

The concentration of ADP in a cell is increasing. Assuming that the cell has plenty of glucose and oxygen available, fatty acid synthesis should:

Decrease

A DNA mutation that affects the primary structure of the alpha-globin protein subunit would also affect the primary structure of the beta-globin protein subunit.

False

A missense mutation could occur in exon 4:

False

Assume the redox potential of cyt-b were to change from +70 to -120. Determine whether each of the following statements is true or false for this scenario. NAD+ would accumulate:

False

Cells arrested in G2 will contain the same quantity of DNA as cells arrested in G1:

False

The diagram below shows an imaginary eukaryotic gene containing two exons. The exon nucleotides are numbered beginning at the transcription start site and a portion of the intron is not shown to save space. Use this diagram to answer each of the questions below. The polyA tail is added immediately after the stop codon:

False

The figure below shows the light-dependent reactions of photosynthesis. Assume that PSII has lost the ability to split water. Determine whether each of the following statements will be true or false based on this scenario. The accessory pigments in PSII will stop transferring energy to each other.

False

The polyA signal sequence is in exon 3:

False

The same cyclin protein will regulate the transition to S phase and the transition to M phase:

False

The stop codon is in exon 4:

False

You used PCR to amplify the human insulin gene from a cDNA template. The target sequence for this PCR reaction is approximately 600 base pairs (bp). To confirm that your PCR worked, you run the PCR products on a gel and obtain the results shown below. The left lane contains DNA fragments of known sizes and the right lane contains your PCR products. Use these results to determine whether each of the following statements is true or false. The correct size target sequence was NOT amplified in this reaction:

False

A eukaryotic gene is most likely to be transcribed if it is located where?

In a region of the genome in which the histones are acetylated

A plant cell is exposed to a toxin that makes the thylakoid membrane freely permeable to protons. As a result of adding this toxin, the amount of NADPH in the chloroplast would most likely:

Increase

The concentration of ADP in a cell is increasing. Assuming that the cell has plenty of glucose and oxygen available, phosphofructokinase (PFK) activity should:

Increase

Which lane contains the DNA fragments produced by digestion of the plasmid with enzymes X and Y and Z?

Lane H

Below on the left is a diagram of double-stranded DNA of a circular plasmid from a bacterial cell. The positions X, Y, and Z are sites where the plasmid DNA is cleaved by restriction enzymes X, Y, and Z, respectively. The numbers are the size in kilobase pairs (kb) of the DNA regions between the restriction sites. On the right is a diagram of an electrophoresis gel. Lane 1 is the ladder, comprised of DNA fragments that range in size from 1-12 kb showing the position of each band size after electrophoresis. The other lanes are DNA bands observed from digestion of the plasmid with one of more of the restriction enzymes. Which lane contains the DNA fragments produced by digestion of the plasmid with enzyme X only?

Lane K

Which lane contains the DNA fragments produced by digestion of the plasmid with enzymes Y and Z?

Lane L

Which lane contains the DNA fragments produced by digestion of the plasmid with enzymes X and Y?

Lane M

Which lane contains the DNA fragments produced by digestion of the plasmid with enzymes X and Z?

Lane Q

The concentration of Waste molecules is ________ inside the cell compared to the outside.

Lower

Imagine that a doctor is culturing two types of cells: one from a malignant melanoma and one from a normal skin sample. How would you expect these two cell populations to differ?

Malignant melanoma cells would have active telomerases that constantly replenish and lengthen telomeres.

When oxygen is depleted, the citric acid cycle stops. What could we add to the system to restore citric acid cycle activity (other than oxygen)?

NAD+ or FAD (Cells that are depleted of oxygen cannot oxidize the NADH and FADH2 that are produced in the citric acid cycle. Thus, there is insufficient NAD+ and FAD for the cycle to continue. Supplying these exogenously might restore the cycle's activity.)

If the RNA transcript 5′-AUGAUCGGAUCGAUCCAU-3′ resulting from the DNA sequence, 5′—ATGATCGGATCGATCCAT—3′, is present in the mRNA and translated codon by codon from one end to the other, which of the polypeptides would correspond to this part of the mRNA? Use the table shown to answer this question.

NH2- Met-Ile-Gly-Ser-Ile-His -COOH (mRNA is translated starting from 5′ end. The first amino acid has a free amino group. The last amino acid has a free carboxyl group.)

The diagram below shows a cell with three different membrane transport proteins. The Na+/K+ Pump is a primary active transporter and the Na+/Waste Co-transporter is a secondary active transporter. Arrows show the direction of net movement of molecules through the Pump and Co-transporter. The Na+ Channel can exist in either a closed state (no Na+ can pass through) or an open state (Na+ can pass through). Use this diagram to answer the questions below. What will happen to the net movement of Waste molecules if the Na+/K+ Pump stops working?

Net movement of Waste out of the cell will continue for some time and then all net movement of Waste in or out of the cell will stop.

Unrepaired single-stranded DNA breaks can lead to double-stranded DNA breaks during the next round of replication. Which repair pathway would be most appropriate for repairing double-stranded DNA breaks?

Nonhomologous end joining

What amino acid does the second codon of this gene's open reading frame encode?

Serine (Ser)

Antinomycin A is a poison that affects the electron transport chain and renders it nonfunctional. In the presence of Antinomycin the Citric Acid Cycle would:

Slow down

Consider a cell in which one of the proteins involved in DNA replication is altered. This alteration results in an increased occurrence of single-stranded DNA breaks in the newly synthesized DNA. Which protein function is most likely nonfunctional in this situation?

The fragment joining function of ligase

Although the phospholipid molecules can be in constant lateral movement, they very rarely flip from one side of the bilayer to the other. Which of the answer choices could explain this?

The head groups are repelled by the hydrophobic membrane interior.

To cells that are defective in primer removal, you add fluorescent ribonucleotides when the cells are undergoing DNA replication. In this case, you observe that one strand glows more than the other not only near the replication fork but also at intervals along its length. Which strand glows in this way and why?

The lagging strand glows in this way because its RNA primers are required for each Okazaki fragment and are closely spaced.

Suppose you add fluorescent ribonucleotides to a cell undergoing DNA replication so that the RNA primers used in DNA synthesis glow when viewed with a fluorescent microscope. You notice that, near each replication fork, one strand glows more than the other. Which strand glows more, and why?

The lagging strand glows more because its RNA primer is nearer the replication fork.

Hypothesis: Protein A is a histone acetyltransferase (HAT).

The results do not provide enough information to support or reject this hypothesis

Hypothesis: Protein B represses (decreases) expression of Gene Y.

The results do not provide enough information to support or reject this hypothesis

A beaker contains two solutions of salt dissolved in water. The two solutions have different concentrations of salt (measured by molarity, M) and are separated by a membrane that is permeable to both salt and water. The salt and water will move through the membrane by diffusion. Which statement is true about the diffusion of these solutions?

There will be a net movement of salt from side B to side A and net movement of water from side A to side B.

What will happen when the Na+ channel is open?

There will be net movement of Na+ into the cell through the channel

Kangaroo rats live in the deserts of the southwestern United States. Kangaroo rats have many adaptations to minimize water loss. They obtain a small amount of water from seeds that they eat. However, the rest of the water they obtain is from cellular respiration.

This could be true, as water is produced in cellular respiration. (For these extremely water-conserving animals, the quantity of water that results from the reduction of O2 at the end of the electron transport chain is very significant and allows them to exist in this dry habitat.)

Hypothesis: Protein A and Protein B can bind the same piece of DNA at the same time.

This hypothesis is rejected by the results

Hypothesis: Protein B can bind DNA.

This hypothesis is supported by the results

You are studying two proteins (A and B) that you think are involved in regulating the expression of Gene Y. You perform a gel shift (EMSA) assay using a regulatory DNA sequence from Gene Y. Each question below represents a hypothesis that you are testing. For each hypothesis, determine whether it is supported or rejected by the results of your EMSA experiment, or whether the results do not provide enough information. Hypothesis: Protein A can bind DNA.

This hypothesis is supported by the results

A nonsense mutation could occur in exon 1:

True

CRP-cAMP will be bound to both copies of the lac operon in this cell:

True

Cells arrested in M will have more condensed DNA than cells arrested in G2:

True

Changing nucleotide 13 from C to A would result in a nonsense mutation:

True

Consider the three sets of gels below. Each set shows an RNA gel and a protein gel for the products of the same gene. For each gel, "WT" indicates the normal wild type products and "Mut" indicates the mutant products. Use these gels to determine whether each of the following statements is true or false. Gel set A could result from a mutation that inhibits the function of the SWI/SNF nucleosome remodeling complex:

True

Gel set B could result from a mutation that causes the gene to be targeted by a histone acetyltransferase (HAT), assuming that WT is not targeted by a HAT:

True

Hemoglobin is a protein found in the cytosol of red blood cells. In humans, it is coded for by two different genes: HBA and HBB. The HBA gene encodes a protein subunit called alpha-globin and the HBB gene encodes a protein subunit called beta-globin. Each of these subunits binds a heme molecule that binds oxygen. A diagram of human hemoglobin is shown below. Use this information to determine whether each of the following statements is true or false. Hemoglobin has quaternary structure:

True

Molecule X could form a hydrogen bond with water

True

One of the primers was able to bind at two locations in the cDNA template:

True

T/F Molecule X contains at least one nonpolar covalent bond

True

T/F Molecule X could form an ionic bond with Na+

True

T/F NADP+ will accumulate in the chloroplast.

True

The diagram below shows a gene with four exons. The reading frame that encodes the protein is shaded and begins in exon 1 and ends in exon 3. Use this diagram to determine whether each of the following statements is true or false. The start codon is in exon 1:

True

You are studying the cell cycle using fission yeast. A model of the fission yeast cell cycle is shown below. You have observed some mutant cells that are much longer than wild type cells. Use these data to determine whether each of the following statements is true or false. Blocking the transition from G1 to S would cause the mutant cells to look this way:

True

In the diagrams below, the horizontal lines represent double-stranded DNA and the numbers are regions within the DNA. The sites labeled W, X, Y, and Z denote the locations of cleavage sites for the restriction enzymes W, X, Y, and Z, respectively. The DNA at the left is located in a bacterial plasmid vector and that on the right is located in chromosomal DNA. Each restriction enzyme produces ends that can pair with the ends of other DNA fragments produced by the same restriction enzyme but not with the ends produced by any of the other enzymes shown. A researcher plans to produce a clone with the genomic DNA inserted into the vector in the orientation 1-4-3-2. Which two enzymes should be used to cleave the vector and the chromosomal DNA to produce complementary ends that will lead to this result?

X and Y

Which one of the choices would most likely contribute to uncontrolled cell proliferation (that is, cancer)?

a mutant CDK that was active in the absence of its cyclin binding partner

The beaker in the illustration contains two solutions of salt with different concentrations (measured by molarity, M). The two solutions are separated by a membrane that is permeable to water but not to salt. What will occur in this container? a. diffusion of water from A to B but no diffusion of salt b. diffusion of water from B to A and of salt from A to B c. diffusion of both water and salt from B to A d. diffusion of salt from B to A, but not of water

a. diffusion of water from A to B but no diffusion of salt

A new experimental pesticide is being tested by a large agricultural chemical company. An unfortunate side effect in plants treated with this new product is a decrease in ATP production in the chloroplasts. (Interestingly, production of ATP in the mitochondria is unaffected.) Which of the answer choices would you expect to be directly affected by the new pesticide? a. the rate of photorespiration b. the transport of electrons along the photosynthetic electron transport chain c. the carboxylation of RuBP by rubisco d. the oxidation of RuBP by rubisco

a. the rate of photorespiration

A large agricultural chemical company is testing a new experimental pesticide. An unfortunate side effect in plants treated with this new product is a decrease in NADPH production in the chloroplasts. (Interestingly, reduction of NAD+ to NADH in the mitochondria is unaffected.) Given this observation, which of the answer choices would you expect to observe in the chloroplasts of these plants?

an increase in 3-phosphoglycerate levels and a decrease in RuBP levels (Low NADPH levels would restrict the reduction phase of the Calvin cycle, causing an accumulation of phosphoglycerate (3-PGA). As the RuBP is consumed by the carbon fixing step, it cannot be replaced, because there is insufficient triose phosphate (G3P) to use in the regeneration phase.)

Where is DNA polymerase found to the left of the dotted line?

both strands

The diagram below represents the replication bubble that has formed at a bidirectional origin of replication. The dotted line shows where replication first began. Use this diagram to answer the questions below. Where does lagging strand synthesis occur to the right of the dotted line?

bottom strand

The gel diagram shown represents analysis of blood from a victim of a crime and from two suspects. Criminologists created this gel using a single tandem repeat site. Which suspect is definitely innocent?

suspect 2 The sample from suspect 1 is consistent with the crime scene sample, though more tandem repeats should be analyzed to make a conclusion about suspect 1's involvement in the crime. Suspect 2 can be ruled out as a suspect because one of his alleles is different from the crime scene sample.

A weapon (W) left behind at a crime scene is typed for a tandem repeat. The DNA from the weapon includes bands from the victim (V) as well as those from the perpetrator. Which of the suspects (A-E) has tandem repeat bands that are consistent with those of the perpetrator?

suspect B Analyzing the pattern of bands in lanes W and V, we can tell which bands belong to the victim (second and fourth from the top). Therefore, bands 1 and 3 belong to one of the suspects. The only suspect who has bands identical to the crime scene sample is suspect B.

The gel diagram shows the bands obtained for a single tandem repeat in evidence obtained at a crime scene (W) and genomic DNA from four suspects (A-E). Which suspect cannot be ruled out as the source of the DNA in the sample?

suspect D

Mismatch repair, base excision repair, and nucleotide excision repair are similar in that each:

uses an undamaged segment of DNA as the template to repair a damaged segment of DNA

The parallel lines shown represent the paired strands of a DNA double helix. If this molecule undergoes one round of replication, which ends are shorter in the daughter molecules than in the parental molecules?

w and z In the lagging strand, which grows away from the replication fork, the final RNA primer is synthesized about 100 nucleotides from the 3ˊ end of the template. Because this primer initiates synthesis of the final Okazaki fragment of the lagging strand, there is no other Okazaki fragment to synthesize the missing 100 base pairs and remove the primer. Therefore, when DNA replication is complete, the new daughter DNA strand will be missing about 100 base pairs from the 3ˊ end.

A strain of E. coli is genetically engineered in which the lacZ and lacY genes are removed and replaced with a gene encoding a fluorescent protein. A copy of the operon in which the protein product fluoresces green is inserted into the chromosome, and a copy in which the protein product fluoresces red is inserted into a plasmid. Both copies carry a wild-type lacO gene, and the cells of the strain have a single copy of the lacI repressor gene. If both fluorescent proteins are expressed, the cells fluoresce yellow (because a combination of red and green fluorescence appears as yellow), and if neither of the fluorescent proteins is expressed, the cells show no fluorescence. If the lacI gene in the genetically engineered fluorescent strain were nonmutant but the lacO sequence on the chromosome mutated to lacOc, how would the cells fluoresce in the presence of inducer? In the absence of inducer?

yellow; green

A strain of E. coli is genetically engineered in which the lacZ and lacY genes are removed and replaced with a gene encoding a fluorescent protein. A copy of the operon in which the protein product fluoresces green is inserted into the chromosome, and a copy in which the protein product fluoresces red is inserted into a plasmid. Both copies carry a wild-type lacO gene, and the cells of the strain have a single copy of the lacI repressor gene. If both fluorescent proteins are expressed, the cells fluoresce yellow (because a combination of red and green fluorescence appears as yellow), and if neither of the fluorescent proteins is expressed, the cells show no fluorescence. If the lacI gene in the genetically engineered fluorescent strain were nonmutant but the lacO sequence on the plasmid mutated to lacOc, how would the cells fluoresce in the presence of inducer? In the absence of inducer?

yellow; red

A strain of E. coli is genetically engineered in which the lacZ and lacI genes are removed and replaced with a gene encoding a fluorescent protein. A copy of the operon in which the protein product fluoresces green is inserted into the chromosome, and a copy in which the protein product fluoresces red is inserted into a plasmid. Both copies carry a wild-type lacO gene, and the cells of the strain have a single copy of the lacI repressor gene. If both fluorescent proteins are expressed, the cells fluoresce yellow (because a combination of red and green fluorescence appears as yellow), and if neither of the fluorescent proteins is expressed, the cells show no fluorescence. If the lacI gene in the genetically engineered fluorescent strain is mutated to an inactive form (lacI-), the cells would fluoresce _____ in the presence of an inducer and _____ in the absence of an inducer.

yellow; yellow

In order to analyze how different components of the lac operon work, scientists created special strains of E. coli, called partial diploids. A partial diploid has one full copy of the lac operon in the bacterial chromosome plus another copy of the lac operon in a plasmid. Hence, for the lac operon (and only the lac operon) the bacterial cell is a diploid. Below is one possible genotype of a partial diploid. The genotype written to the left of the slash (/) is that of the lac operon in the bacterial chromosome, and the genotype written to the right of the slash is that of the lac operon in the plasmid. I+ P- O+ Z+/ I- P+ O+ Z- For the partial diploid genotype shown here, determine whether functional β-galactosidase is synthesized in the absence and in the presence of lactose.

β-galactosidase is not produced whether lactose is present or absent.