LS7A: Week 7

Modifications of histone tails can: affect expression of some genes in response to the environment. affect chromatin structure. repress transcription of some genes. activate transcription of some genes. All of these choices are correct.

All of these choices are correct.

The idea that the expression of some genes is controlled by the products of other genes was originally criticized in this way: If n genes were to be controlled, then another n genes would be needed to control them, and then another n genes would be needed to control the controllers, and so on and on. How does combinatorial control help refute this criticism?

Combinatorial control requires far fewer genes because there is not a one-to-one correspondence between the genes that are regulated and those that do the regulating. The transcription factors produced by a relatively small number of regulatory genes can, in various combinations, control the expression of a far larger number of target genes. As an analogy, consider the virtually limitless combinations of sounds that can be played on a standard piano that has only 88 keys (36 black and 52 white).

It is necessary for the gene that codes for the repressor of lac operon to be near the structural genes. True False

False

The methylation state of an individual CpG island: is fixed; such genes are permanently turned off. can change over time in response to environmental cues, but this has no effect on gene expression. can change over time in response to environmental cues, allowing genes to be turned on or off as needed. is fixed, but this has no effect on whether genes are expressed. is random sometimes the cytosines are methylated and sometimes they're not, but the state is independent of the environment or cell type.

can change over time in response to environmental cues, allowing genes to be turned on or off as needed.

Transcription of a gene can be increased or decreased according to the: proportion of arginine and lysine amino acids in the histone proteins. combination of histone proteins found within the nucleosome. coding sequences in the messenger RNAs for histone proteins. combination of amino acid modifications in the histone tails.

combination of amino acid modifications in the histone tails.

Alternative splicing allows for: different polypeptides to be made from a single gene. two or more different proteins to be made from a single processed mRNA. enhanced recognition of an mRNA by a ribosome. increased stability of a mature mRNA. multiple genes to be used to code for a single polypeptide chain.

different polypeptides to be made from a single gene.

Chromatin remodeling refers to the process by which: mutations change DNA structure and therefore chromatin structure. nucleosomes are repositioned to expose different stretches of DNA to the nuclear environment. methylation occurs in CpG islands. DNA strands are "straightened out" to allow access to the proteins that carry out transcription. DNA strands are "unzipped" to allow access to the proteins that carry out transcription

nucleosomes are repositioned to expose different stretches of DNA to the nuclear environment.

A region of prokaryotic DNA consisting of an operator, promoter, and coding sequence for several functionally related genes is called a(n): opera. organized genomic region. operon. closed reading frame.

operon.

In prokaryotes, inducers are small molecules that bind to _____ and _____ transcription. repressors; inhibit activators; promote None of the answer options is correct. repressors; promote activators; inhibit

repressors; promote

In the lactose operon of E. coli, the lacZ and lacY genes are: structural genes. operators. repressors. promoters. inducers.

structural genes.

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 (and the accompanying allolactose that is the actual inducer). β-galactosidase is produced when lactose is present but is not produced when lactose is absent. β-galactosidase is not produced when lactose is present but is produced when lactose is absent. β-galactosidase is produced whether lactose is present or absent. β-galactosidase is not produced whether lactose is present or absent.

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

Predict the consequence of a mutation in the lacI repressor gene that produces repressor protein that is able to bind to the operator, but not able to bind allolactose.

A mutation in the repressor gene that does not allow the repressor protein to bind allactose means that the repressor will never be blocked from binding the lactose operon promoter. This will lead to a cell that is not able to produce β-galactosidase in the presence or absence of lactose. In other words, the lactose operon will not be inducible.

The model of clustering genes into operons is commonly found in both prokaryotes and eukaryotes. Question 4 choices Choice A., true Choice B., false

B, False b/c operons can only be found in prokaryotes(polycistronic mrna)

One difference between eukaryotic and prokaryotic DNA packaging is: eukaryotic cells have fewer genes than prokaryotic cells. prokaryotic cells have different nucleotides that are smaller than eukaryotic cells. prokaryotic cells have smaller chromosomes and thus fit into the cell unaltered. DNA wraps around histones in eukaryotic packaging.

DNA wraps around histones in eukaryotic packaging.

One difference between eukaryotic and prokaryotic DNA packaging is: prokaryotic cells have different nucleotides that are smaller than eukaryotic cells. eukaryotic cells have fewer genes than prokaryotic cells. DNA wraps around histones in eukaryotic packaging. prokaryotic cells have smaller chromosomes and thus fit into the cell unaltered.

DNA wraps around histones in eukaryotic packaging.

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: True False Repressor protein will be bound to both operators in this cell: True False CRP-cAMP will be bound to both copies of the lac operon in this cell: True False

F, F, T

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 methylated In a heterochromatic region of teh genome In a region of the genome in which the histones are acetylated In a region of the genome in which the histones are unmodified

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

For the lactose operon, the CRP-cAMP is a(n): operator. repressor. activator. inducer. promoter.

activator.

An activator protein combines with a small molecule and undergoes a change in shape that alters its binding affinity to DNA. This change in shape is an example of: allosteric effect. induced silencing. activator effect. position effect. dosage compensation.

allosteric effect.

Which of the following processes produce different proteins in different cells from the same primary transcript? (Select all that apply.) alternative splicing RNA editing histone modification combinatorial control chromatin remodeling

alternative splicing RNA editing

The lactose operon is under positive control by the CRP-cAMP complex. In order for the operon to be fully inducible, the CRP-cAMP complex must be: (Select all that apply.) absent from the regulatory region of the operon. at high concentration. at low concentration. bound to the regulatory region of the operon.

at high concentration. bound to the regulatory region of the operon.

In prokaryotes, repressor proteins: (Select all that apply.) are part of the mechanism of positive regulation. are part of the mechanism of negative regulation. bind with activators and prevent transcription. bind with DNA and prevent transcription.

bind with DNA and prevent transcription. are part of the mechanism of negative regulation.

Alternative splicing means that: some transcripts are spliced correctly and others incorrectly. some transcripts are spliced while others are not. alternating introns are removed. different spliced forms contain different combinations of exons.

different spliced forms contain different combinations of exons.

The CRP-cAMP complex binds the lactose operon when: None of the answer options is correct. glucose levels are low and cAMP levels are high. glucose levels and cAMP levels are low. glucose levels are high and cAMP levels are low. glucose levels and cAMP levels are high.

glucose levels are low and cAMP levels are high.

Positive and negative transcriptional regulation differ in that: in positive regulation, the binding of a regulatory protein to the DNA is necessary for transcription to occur; in negative regulation, such binding prevents transcription. in positive regulation, the absence of a regulatory protein promotes transcription; in negative regulation, the absence of a regulatory protein promotes transcription. in positive regulation, the binding of a regulatory protein to the DNA is necessary for transcription to occur; in negative regulation, no such protein is necessary. None of the answer options is correct. positive regulation requires that a promoter be present; a promoter is not necessary in negative regulation.

in positive regulation, the binding of a regulatory protein to the DNA is necessary for transcription to occur; in negative regulation, such binding prevents transcription.

For the lactose operon, lactose is a(n): repressor. promoter. inducer. operator. activator.

inducer.

A mutant strain of E. coli is found that produces both β-galactosidase and permease constitutively. What are the MOST likely mutations in this strain? (Select all that apply.) lacOc lacZ- and lacY- mutation in CRP-cAMP binding site lacP- lacI-

lacOc, lacI-

The lacZ and lacY genes are transcribed when: glucose levels are high and lactose levels are low. glucose levels are low, regardless of the level of lactose in the cell. lactose is present, regardless of the level of glucose in the cell. lactose is absent and glucose levels are high. lactose is present and glucose levels are low.

lactose is present and glucose levels are low.

X-inactivation is caused by the accumulation of: None of the answer choices accurately describes the process of X-inactivation. noncoding RNA produced by the Xist gene, which coats the X chromosome and covalently crosslinks the DNA strands preventing them from being unwound, "unzipped," and transcribed. coding RNA produced by the Xist gene; this RNA, in addition to coding for Xist proteins, binds to and coats the X chromosome undergoing inactivation and physically prevents it from being transcribed. proteins produced by the Xist gene; these proteins induce methylation, histone modification, and other changes associated with preventing transcription. noncoding RNA produced by the Xist gene, which coats the X chromosome and induces DNA methylation, histone modification, and other changes associated with preventing transcription.

noncoding RNA produced by the Xist gene, which coats the X chromosome and induces DNA methylation, histone modification, and other changes associated with preventing transcription.

One regulatory step in the process of gene expression and synthesis of proteins is the actual modification of proteins themselves, which is called: transcriptional modification. alternative splicing. post-protein modification post-translational modification alternative modification

post-translational modification

An operon is a: region of DNA consisting of the operator and coding sequences for structural proteins. gene coding for a repressor protein. single molecule of RNA coding for more than one protein. region of DNA consisting of the promoter, the operator, and coding sequences for structural proteins. region of DNA consisting of the promoter and operator sequences needed to regulate one or more structural genes.

region of DNA consisting of the promoter, the operator, and coding sequences for structural proteins.

Enhancer sequences are bound by: cytosine methylation enzymes. RNA splicing complexes. transcription factors. histone-modifying complexes. RNA editing complexes.

transcription factors.

In general, when cytosine bases in CpG islands are methylated: transcription is active and rapid. translation is repressed. transcription is active, but slow. transcription is repressed. translation is active and rapid.

transcription is repressed.

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. 4. 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; red yellow; green yellow; no fluorescence None of the other answer options is correct. yellow; yellow

yellow; green

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? None of the other answer options is correct. yellow; red yellow; yellow yellow; no fluorescence yellow; green

yellow; red