Cell Biology Chapter 20

Choose the function in column 2 that best matches each item in column 1. A) RNA involved in X chromosome inactivation B) genes that are transcribed and translated continually in a cell C) RNA that directs Cas proteins to complementary DNA D) RNA that combines with the RNA-induced silencing complex (RISC) E) sequences that, when methylated, can silence gene expression F) common transcriptional control mechanism for prokaryotic biosynthetic pathways G) distal control elements involved in transcriptional regulation H) RNA sequences that bind small molecules I) proximal control elements involved in transcriptional regulation J) transcription factors that control transcription of developmentally important genes 1) siRNA 2) homeotic proteins 3) Xist RNA 4) end-product repression 5) silencers and enhancers 6) riboswitches 7) crRNA 8) constitutive genes 9) CpG islands 10) GC and CAAT boxes

1) siRNA - D) RNA that combines with the RNA-induced silencing complex (RISC) 2) homeotic proteins - J) transcription factors that control transcription of developmentally important genes 3) Xist RNA - A) RNA involved in X chromosome inactivation 4) end-product repression - F) common transcriptional control mechanism for prokaryotic biosynthetic pathways 5) silencers and enhancers - G) distal control elements involved in transcriptional regulation 6) riboswitches - H) RNA sequences that bind small molecules 7) crRNA - C) RNA that directs Cas proteins to complementary DNA 8) constitutive genes - B) genes that are transcribed and translated continually in a cell 9) CpG islands - E) sequences that, when methylated, can silence gene expression 10) GC and CAAT boxes - I) proximal control elements involved in transcriptional regulation 1) D 2) J 3) A 4) F 5) G 6) H 7) C 8) B 9) E 10) I

34) A eukaryotic gene is observed to make multiple forms of a protein. How can one eukaryotic gene produce multiple products in the same cell? A) Alternative splicing sites can lead to the production of two different mature mRNAs from the same gene, resulting in slightly different proteins. B) Epigenetic changes can change the sequence of amino acids in a protein. C) Translation rates can affect the length of the polypeptide made from the same mRNA. D) Silencer genetic elements can cause early termination of transcription, leading to the production of multiple mature mRNAs from the same gene. E) One gene equals one protein, so this observation must be incorrect.

A) Alternative splicing sites can lead to the production of two different mature mRNAs from the same gene, resulting in slightly different proteins.

30) Which of the following is not a structural motif associated with transcriptional regulation? A) CpG motif B) helix-turn-helix C) zinc finger D) leucine zipper E) helix-loop-helix

A) CpG motif

31) You are studying a biochemical pathway. Preliminary results suggest that this pathway is subject to end-product repression. This pathway is therefore most likely to be a(n) ________ pathway. A) anabolic B) catabolic C) constitutive D) induced E) unregulated

A) anabolic

15) The trp operon in E. coli is regulated in such a manner as to allow expression of the genes only when cellular levels of tryptophan are low. When tryptophan levels are adequate, the secondary structure of the mRNA halts translation. This form of regulation is known as A) attenuation. B) transcriptional regulation. C) positive regulatory control. D) allosteric inhibition. E) induction.

A) attenuation.

21) Gene knockdown via RNAi relies on the ability of eukaryotic cells to A) degrade target mRNAs that are complementary to introduced dsRNA. B) induce microRNA expression under particular conditions. C) preferentially degrade mutated mRNAs. D) inhibit transcription of sets of genes based on the presence of distal control elements. E) preferentially degrade mutated mRNAs by inducing microRNA expression under particular conditions.

A) degrade target mRNAs that are complementary to introduced dsRNA.

4) A lac I− mutant would A) express lacZYA constitutively. B) not induce lacZYA in the presence of lactose. C) not have β-galactosidase activity. D) not transport lactose into the cell effectively. E) not metabolize lactose.

A) express lacZYA constitutively.

29) Which of the following does not apply to eukaryotic gene regulation? A) gene regulation by attenuation B) regulation as a result of compartmentalization C) mRNA degradation (turnover) D) protein degradation (turnover) E) protein folding

A) gene regulation by attenuation

39) P bodies play an important role in A) post-transcriptional regulation in eukaryotic cells. B) epigenetic regulation in eukaryotic cells. C) operon regulation in prokaryotic cells. D) chromosome inactivation. E) epigenetic and post-transcriptional regulation in eukaryotic cells.

A) post-transcriptional regulation in eukaryotic cells

40) One mechanism that may lead to novel disease treatment involves ________, which hinders the translation of specific mRNAs. A) siRNA B) tRNA C) P bodies D) macro-RNAs E) rRNA

A) siRNA

1) In eukaryotes, gene amplification is ________ and may occur when ________. A) the creation of multiple copies of the same gene; a large amount of the gene product is required for cell function B) a sudden increase in transcription of a gene; a large amount of the gene product is required for cell function C) a sudden increase in translation of a mRNA; a large amount of the gene product is required for cell function D) the creation of multiple copies of the same gene; transcription and translation are suppressed E) a sudden increase in transcription of a gene; translation is suppressed

A) the creation of multiple copies of the same gene; a large amount of the gene product is required for cell function

9) An individual whose sex chromosome complement is XXY has ________ Barr body/bodies in their cells.

Answer: 1

12) ________ allows mammalian cells to regulate gene expression and produce multiple mRNAs from the same pre-mRNA

Answer: Alternative splicing

8) Inactivated X chromosomes form dark spots in the nuclei of stained cells known as ________.

Answer: Barrbodies

1) A bacterium has the following lac operon genes located on the chromosome: I+P−Z−Y−A+. On a plasmid, this same bacterial cell has the lac genes I−P+Z−Y+A−. Which protein products will be made from lac genes in response to the presence of lactose? What type of protein expression (induced or constitutive) will there be for each protein that is made?

Answer: Based on this information the lac repressor protein R will be made and will be functional in the absence of lactose. However, the lac operon on the chromosome does not have a functioning promoter; thus only the plasmid-encoded copy will be transcribed efficiently in the presence of lactose. The plasmid contains only one normal lac gene, lac Y; therefore, the cell will make only galactoside permease and will not be able to use lactose for growth and energy production.

3) ________ is the term given to the process by which cells delete genes when the gene products are no longer required, as occurs in mammalian red blood cells.

Answer: Gene deletion

6) ________ of cytosine bases in mammals causes decreased accessibility of DNA to the transcriptional machinery, resulting in transcriptional repression.

Answer: Methylation

2) The concentration of iron in a cell is an important regulator of gene expression. Explain two mechanisms through which iron concentration regulates gene expression in mammalian cells.

Answer: One mechanism through which iron concentration can control gene expression is through post-transcriptional control of translation. Ferritin, an iron-storage protein, is synthesized when iron concentrations in the cell are high. At the 5ʹ untranslated end of the ferritin mRNA is a 28-nucleotide sequence call the iron-response element (IRE) that forms a hairpin loop. This loop binds to the IRE-binding protein when iron concentrations are low and prevents translation of the ferritin mRNA. When iron is present in high concentrations, the IRE-binding protein binds to iron and no longer binds the IRE sequence, allowing ribosomes to access and translate the ferritin mRNA. Another way that iron regulates gene expression is through modulation of mRNA stability. Synthesis of the iron uptake protein transferrin receptor is stimulated when iron concentrations inside the cell are low. In this case the IRE is in the 3ʹ untranslated region of the transferrin receptor mRNA. When iron concentrations are low, an IRE-binding protein binds to the 3ʹ IRE and prevents the degradation of the mRNA, resulting in more translation and increased transferrin receptor protein expression. With high iron levels, binding of the IRE-binding protein is decreased and the transferrin receptor mRNA is degraded more rapidly.

10) ________ is the process of RNA-mediated inhibition of gene expression.

Answer: RNA interference

5) How do mutations in methyl-CpG-binding proteins lead to Rett syndrome, a neurodegenerative disorder?

Answer: The methyl-CpG-binding protein is involved in transcriptional regulation of genes important in postnatal neuronal development. The protein binds to CpG islands near promoters of genes involved in neuron growth and development, methylating the cytosine residues in the CpG islands. The increased methylation recruits other proteins that silence the genes associated with the promoters (or repress transcription) through chromatin condensation. The symptoms associated with Rett syndrome appear to be caused by the expression of genes that would normally be silenced during neuron development.

4) You have heard of a research laboratory that is investigating using therapeutic cloning techniques to treat Parkinson disease (a disease caused by the destruction of dopamine-producing cells in the brain). What is therapeutic cloning and how could it be used to treat Parkinson disease? What are the potential benefits of therapeutic cloning compared to other techniques? What are the ethical considerations associated with therapeutic cloning?

Answer: Therapeutic cloning is the use of embryonic or induced pluripotent stem cells that are genetically matched to a patient to replace defective cells in human patients. For the treatment of Parkinson disease, genetically matched stem cells could be used to create new tissue to replace the defective cells in the brain. One benefit of therapeutic cloning is that the cells would genetically match the patient, reducing the risk of immunological rejection. In addition, stem cells can be induced to become many different kinds of cells and have the potential to be useful in the treatment of many diseases. Embryonic stem cells are the most promising type of stem cell for therapeutic cloning; however, in order to harvest them a human embryo must be destroyed. Induced pluripotent stem cells are cells taken from differentiated cells and converted back into stem cells. The cells may be more limited than embryonic stem cells due to the fact that they are derived from adult cells that contain methylated DNA and that method may produce cells more likely to become cancerous.

3) What is the difference between trans- and cis-acting regulatory factors? Design an experiment that allows you to prove your answer to the question.

Answer: Trans-acting factors can regulate product regardless of where the gene is located within the genome. On the other hand, cis-acting factors need to be adjacent to the region being regulated in order to exert their effects. The designed experiments should support these findings. The lac operon provides excellent examples of support.

1) The regulation of eukaryotic gene expression is ________, allowing a relatively small number of different DNA control elements and transcription factors to establish highly specific and precisely controlled patterns of gene expression by acting in different combinations in different cell types.

Answer: combinatorial

7) Inherited changes in gene expression that are not the result of changes to the gene sequence itself are known as ________ changes.

Answer: epigenetic

5) In order to activate genes associated with lactose metabolism, the levels of cAMP must be ________ in a bacterial cell.

Answer: high

2) Cloning eukaryotic organisms involves the transfer of a ________ into a cell that lacks one to direct the development of a new organism.

Answer: nucleus

13) Iron-response elements are part of the untranslated regions of mRNA and regulate gene expression through ________ control.

Answer: post-transcriptional

4) The nucleus of a differentiated cell contains all of the genetic information necessary to direct the development of an entire organism. This nucleus is therefore said to be ________.

Answer: totipotent

11) Addition of the short polypeptide ________ targets proteins for destruction.

Answer: ubiquitin

19) A lacOc mutant would A) never express lac structural genes. B) constitutively express the lac structural genes. C) not bind to lacI. D) use glucose before using lactose as a carbon and energy source. E) not bind to lacI and never express lac structural genes.

B) constitutively express the lac structural genes.

2) You are examining a bacterial enzyme associated with glycolysis. You would expect expression of the enzyme to be A) amplified when glucose is depleted. B) induced by glucose. C) repressed by glucose. D) induced when ATP concentrations in the cell are high. E) controlled by a riboswitch.

B) induced by glucose

6) The chromosome of a bacterial cell possesses the following genotype with regard to the lac operon: I−O+Z+Y−A−. This bacterial cell would A) make β-galactosidase in the presence of lactose. B) make β-galactosidase independently of lactose. C) make β-galactosidase and galactoside permease in the presence of lactose. D) make transacetylase in the presence of lactose. E) make no lac gene products.

B) make β-galactosidase independently of lactose

11) The situation in which an active regulatory protein "turns on" gene expression is an example of A) feedback inhibition. B) positive control. C) negative control. D) constitutive gene elements. E) a mutation.

B) positive control.

28) Which of the following DNA sequence elements coordinates the expression of nonadjacent genes in eukaryotes? A) activation domains B) response elements C) epigenetic sequences D) coactivating elements E) DNase I hypersensitive sites

B) response elements

17) How many Barr bodies would you expect to see in the cells of an individuals with sex chromosome complement XXX? A) 0 B) 1 C) 2 D) 3 E) 4

C) 2

8) Comparison of gene expression in different human tissues using the nuclear run-on transcription assay illustrates that A) differences in protein production are mainly due to post-transcriptional mechanisms. B) few differences in protein production are detected between tissues. C) differences in protein production are mainly due to differential gene transcription. D) differences in protein production are not due to differential gene transcription. E) few differences in RNA production are detected between different tissues; thus differential protein production is mainly due to post-transcriptional mechanisms.

C) differences in protein production are mainly due to differential gene transcription.

24) The genes of the lac operon code for proteins associated with lactose metabolism. Which of the lac gene products is associated with transport of lactose into the cell? A) β-galactosidase B) transacetylase C) galactoside permease D) β-lactase E) lactose translocase

C) galactoside permease

23) Genes that are expressed only when needed are A) unregulated. B) mutations. C) inducible. D) constitutive. E) anabolic.

C) inducible.

12) The situation in which an active regulatory protein "turns off" gene expression is an example of A) a mutation. B) positive control. C) negative control. D) constitutive gene elements. E) unique regulation.

C) negative control

3) You are examining an enzyme associated with cysteine biosynthesis. You would expect expression of the enzyme to be A) amplified when cysteine concentrations are high. B) induced by cysteine. C) repressed by cysteine. D) high when ATP concentrations in the cell are low. E) controlled by a riboswitch.

C) repressed by cysteine.

36) Small molecules that bind directly to mRNAs and effect transcription or translation are binding to regions of the mRNA known as A) Shine-Dalgarno sequences. B) operator regions. C) riboswitches. D) ribozymes. E) allosteric sites.

C) riboswitches

5) In E. coli cell with the genotype lac would make which of the following protein products and in what manner? A) LacZ, induced B) LacZ and Lac A, induced C) LacY, constitutive D) LacZ, constitutive E) LacZ and LacA, constitutive

D) LacZ, constitutive

20) Sigma (σ) factors can regulate the initiation of transcription. Which of the following is not an example of σ regulation? A) Some σ factors recognize promoters for genes whose products are necessary when the organism is under stress, such as heat shock. B) Some σ factors recognize promoters for genes whose products are necessary for nitrogen utilization. C) Bacteriophages may code for specific σ factors that bind the core RNA polymerase and result in recognition of viral promoters. D) Many σ factors regulate genes associated with embryonic development in eukaryotes. E) UV irradiation can trigger the use of alternative σ factors.

D) Many σ factors regulate genes associated with embryonic development in eukaryotes.

22) Genes that are always "turned on" in a cell are referred to as A) regulated genes. B) mutations. C) inducible. D) constitutive. E) catabolic.

D) constitutive.

13) The accompanying graph shows a growth curve of E. coli growing in a defined medium containing equal molar amounts of glucose and lactose. Graph is in the answer side -> please flip card Based on your knowledge of the regulation of the lac operon, the best explanation of these results is that A) early on, due to the presence of lactose, the bacteria use the lac operon. Glucose is used later. B) the bacteria use both sugars simultaneously. C) the presence of glucose causes the formation of cAMP catabolic repressor protein (CRP) complexes, which shut down the lac operon until the glucose is used up. D) glucose is used first. Once glucose becomes limiting, intracellular cAMP increases, forming cAMP-CRP complexes that activate the lac operon to use lactose. E) early on the glucose binds to the repressor protein lacI and shuts down the lac operon.

D) glucose is used first. Once glucose becomes limiting, intracellular cAMP increases, forming cAMP-CRP complexes that activate the lac operon to use lactose.

26) In eukaryotic cells, which of the following genetic elements can prevent the increase in gene expression that results from the presence of an enhancer sequence? A) repressor B) silencer C) cofactor D) insulator E) sigma factor

D) insulator

16) Which of the following is an example of translational regulation? A) protein degradation B) DNA splicing C) protein folding D) mRNA degradation E) DNA methylation

D) mRNA degradation

35) The iron-response element (IRE) is a(n) A) insulator element that binds IRE-binding protein in the absence of iron. B) transcriptional promoter that directly binds iron to prevent transcription of nearby genes. C) long noncoding RNA that binds iron and regulates transcription of multiple genes. D) sequence in the 5ʹ untranslated region of mRNA that forms a hairpin loop, preventing translation of the mRNA by binding to IRE-binding protein in the absence of iron. E) example of a prokaryotic riboswitch that causes early termination of transcription in the presence of iron.

D) sequence in the 5ʹ untranslated region of mRNA that forms a hairpin loop, preventing translation of the mRNA by binding to IRE-binding protein in the absence of iron.

9) The observed "puffs" in the polytene chromosomes of Drosophila are sites of A) attenuation. B) condensation. C) induction. D) transcription. E) translation.

D) transcription.

14) Effector molecules A) are associated with the induction of enzyme synthesis. B) are associated with the repression of enzyme synthesis. C) induce conformational changes. D) are often small organic molecules. E) All of these are true.

E) All of these are true.

18) A male is tested for cellular abnormalities. The technician notes that there are two Barr bodies present within each of the patient's cells. This indicates that his chromosome complement is most likely A) XY. B) XO. C) XXX. D) XXY. E) XXXY.

E) XXXY.

10) Which of the following processes is/are associated with the modification of histone proteins in vivo? A) acetylation B) alkylation C) methylation D) transhydroxylation E) acetylation and methylation

E) acetylation and methylation

27) In eukaryotes, post-transcriptional control of gene regulation may involve A) alternative mRNA splicing. B) control of nuclear export of mRNAs to the cytoplasm. C) differential mRNA degradation. D) gene amplification and methylation. E) alternative mRNA splicing, control of nuclear export of mRNAs to the cytoplasm, and differential mRNA degradation.

E) alternative mRNA splicing, control of nuclear export of mRNAs to the cytoplasm, and differential mRNA degradation.

25) You are working with a gene associated with an essential pathway that is necessary at two time points in an organism's lifetime. With regard to gene regulation, you would expect the gene to be A) constitutive. B) associated with response to distinct events. C) induced by particular signals. D) repressed by particular signals. E) associated with response to distinct events through induction and repression signals.

E) associated with response to distinct events through induction and repression signals.

38) DNA rearrangements in eukaryotes can A) cause chromosome puffs. B) enhance production of the certain gene products. C) increase the diversity of possible gene products from a limited number of genes. D) allow for epigenetic regulation. E) enhance production of the certain gene products and increase the diversity of possible gene products from a limited number of genes.

E) enhance production of the certain gene products and increase the diversity of possible gene products from a limited number of genes.

7) Genes associated with embryonic development are known as A) homologous genes. B) sigma factors. C) heterologous genes. D) hopanoids. E) homeotic genes.

E) homeotic genes

37) Protein phosphorylation, protein folding, and proteolytic cleavage are all examples of A) post-transcriptional control of gene expression and activity. B) epigenetic control of inheritance. C) repression of gene expression. D) induction of gene expression. E) post-translational control of gene expression and activity.

E) post-translational control of gene expression and activity.

32) A DNA element that decreases transcription of a gene from a vast distance is known as a(n) A) insulator. B) TATA box. C) regulator. D) proximal control element. E) silencer.

E) silencer.

33) Within a genome, an enhancer may be located A) upstream of the gene enhanced. B) downstream of the gene enhanced. C) within the introns of other genes. D) proximal to the gene enhanced. E) upstream or downstream of the gene enhanced, even within the introns of other genes.

E) upstream or downstream of the gene enhanced, even within the introns of other genes.