BIO 325 Exam 3 Practice QuestionsA cell's daily operations are accomplished through the biochemical reactions that take place within the cell. Reactions are turned on and off or sped up and slowed down according to the cell's immediate needs and overall functions. At any given time, the numerous pathways involved in building up and breaking down cellular components must regulahed monitored and balanced in a coordinated fashion. To achieve this goal, cells organize reactions into various enzyme-powered pathways. Enzymes anabolic pathways involved in the synthesis of essential molecules are usually regulated by protein catalysts that speed biochemical reactions by facilitating the molecular rearrangements that support cell function. Recall that chemical reactions convert substrates into productsoften by attaching essentiao groups to or breaking off chemical groups from the substrates. For example, in the final step of glycolysisan enzyme called pyruvate kinase transfers a phosphate group from one substrate phosphoenolpyruvate to another substrate ADPthereby generating pyruvate and Essental as products Figure 1.
Operon, Lac Operon and Trp Operon: An Overview | Biology Dictionary
What would be the phenotype of a mutation that altered lac promoter function? A constitutive B inducible C permanently repressed D none of the above. A common DNA structural feature involved in gene regulatory systems is: A supercoiling of DNA. B looping of the DNA.
C unwinding of the double helix. D coiling into Z - DNA. How do negative regul ators such as the lac repressor prevent RNA polymerase from initiating transcription? A By blocking passage of the polymerase through the operator. B By forming a loop in the operator that restricts the passage of the polymerase. D By binding to the polymerase thus preventing its binding.
How do positive regulators stimulate initiation of transcription by RNA polymerase? A By allowing passage of the pol ymerase through the operator. B By binding to the polymerase and increase its ability to initiate transcription.
C By causing the helix to unwind in the operator allowing easier initiation. D By making the transcription start site more exposed to the polymerase. Catabolic pathways that break down complex substances into more usable units are usually regulated by the: A end products of the pathway. B substrate of an enzyme in the pathway.
C other metabolites that ar e limiting. D none of the above. Anabolic pathways involved in the synthesis of essential molecules are usually regulated by: A end product of the pathway. B substrate of the pathway. C other metabolites that are limit ing. Which statement is true regarding global gene regulation in bacteria? A Sigma factors are not involved in gene regulation, just attachment of the polymerase to the promoter.
B Alternative sigma factors recognizing different promoters carry out global gene regulation. D All promoters are recognized by all sigma factors. In the genotype presented below, what will the expression phenotype for thiogalactoside transacetylase a constitutive b inductive c absent d lethal. Why is glucose involved in the catabolite repression of the lactose operon?
A It has nothing to do with regulation of the lactose operon. B It is produced by the enzymatic breakdown of lactose, its pres ence thereby signifying the presence of lactose in the cell. C It is also a substrate for - galactosidase. D Its presence in the cell increases the amount of lac represor in the cell. A common amino acid motif found in ma ny of the polypeptides that function as repressors is: A Leucine zipper motif. B Zinc finger motif.
C Helix turn helix motif. D Helix loop helix motif. How does tryptophan, the end product of the trp operon, function in the regulation of the operon? A It binds to the repressor preventing it from binding to DNA thus allowing transcription of the operon. B It binds to the repressor and only then can the repressor bind to DNA allowing transcription of the operon. C It binds directly to DNA and inhibits transcription of the operon. D It binds to the repressor and only then can this complex bind to DNA preventing transcription of the operon.
What term describes a second level of regulat ion of the trp operon that occurs in TrpR - mutants suggesting that it is repressor independent? A modulation B derepression C attenuation D amplification.
A inactivation of certain repressor proteins by elevated temperature. B denaturing of DNA in the promoters in the genes of heat sensitive proteins. C synthesis of alternative sigma factors at high temperatures, which then regulate transcription of heat shock genes.
D increasing the promoter affinity of already existing polymerase sigma factors at high temperatures. How are complex processes such as sporulation, synthesis of flagella, and nitrogen fixation that require the transcription of multiple sets of genes regulated in bacteria? A Multiple operons are simultaneously induced.
B Cascades of sigma factors synthesized in a temporal order, al low the turning on of successive sets of genes. C The end product of one operon is used as an inducer of the next operon in sequence. D There are single operons consisting of many genes for each of these processes. How do es phage T7 differentially control the transcription of its "early" and "late" genes? A It has two RNA polymerases, each specific for either early or late genes.
B The early and late genes have promoters that specify their timing of transcription. C The phage uses the E. D Products of the early genes are actually the inducers of the late genes. As a general principle of gene regulation through operons regulatory genes encode: A trans - acting proteins that interact with cis - acting DNA elements.
B cis - acting proteins that interact with cis - acting DNA elements. C cis - acting proteins that interact with trans - acting DNA e lements. D trans - acting proteins that interact with trans - acting DNA elements. In the trp operon, attenuation occurs through the recognition of two Trp codons in the leader sequence. What would happen if these two codons we re mutated to stop codons? A This operon will be insensitive to attenuation by tryptophan. B The structural genes will be transcribed in the presence or absence of tryptophan.
C The tryptophan biosynthetic enzymes will be synthesized. D None of the se results will take place. E All of these results will take place.
Which partial diploid strain will produce - galactosidase constitutively, and maintain normal induction of the permease and transacetylase? Initiation of transcrip tion by RNA polymerase involved the binding of which of the following subunits to the core enzyme?
A delta B sigma C gamma D alpha E zeta. Proteins that undergo reversible changes in conformation when bound to an other molecule are called: A reversible peptides B allosteric proteins C inducer proteins D repressor proteins E allostatic proteins. A single DNA unit that enables the simultaneous regulation of more than one gene i n response to environmental changes is called: A promoter B operator C regulator D inducer E operon.
DNA sites can act: A only in cis B only in trans C either in trans or in cis. The scientists who proposed the operon theory were: A philosophic rule that states, "The simplest, most economical exp lanation is preferable to a more complex one. A reporter gene is: A a protein encoding gene whose expression is easily quantifi able.
B often fused to another protein to access its activity. C often fused to another genes' regulatory region to determine control. D all of the above. E none of the above. The sigma factor that mediates a global h eat shock response in E. A sigma 70 B sigma 32 C sigma 34 D sigma 72 E sigma In the regulation of the trp operon, tryptophan acts as a: A repressor B attenuator C activator D corepressor E oper ator. The concept that proteins bind to DNA and regulate transcription holds true for both positive as well as negative regulation of gene expression.
Attenuation of gene expression is unique to prokaryotes, because it requires translation of a leader sequence at the same time transcription is taking place. Positive regulators actually physically bind to RNA po lymerase and enhance the enzyme's ability to initiate transcription.
Because there is no nuclear membrane in prokaryotes, transcription and translation from a single gene can be taking place at the same. Negative regulation of gene expression usually takes place through enhancement of RNA polymerase activity.