Becker's World of the Cell (9th Edition)
9th Edition
ISBN: 9780321934925
Author: Jeff Hardin, Gregory Paul Bertoni
Publisher: PEARSON
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Chapter 20, Problem 20.4PS
Attenuation in 25 or Fewer Words. Complete each of the following statements about attenuation of the trp operon of E. coli in 25 or fewer words.
(a) The leader sequence can be considered to be a conditional terminator because …
(b) When the gene product of the operon is not needed, the 5′ end of the mRNA forms a secondary structure that …
(c) Implicit in our understanding of the mechanism of attenuation is the assumption that ribosomes follow RNA polymerase very closely. This “tailgating” is essential to the model because …
(d) Measurements of rates of synthesis indicate that translation normally proceeds faster than transcription. This supports the proposed mechanism for attenuation because …
(e) If the operon encoding the enzymes in the biosynthetic pathway for amino acid X is subject to this type of attenuation, the leader sequence probably encodes a polypeptide that …
(f) Attenuation makes sense as a mechanism for regulating operons that enzymes involved in amino acid biosynthesis because …
(g) Attenuation of this type is not a likely mechanism for regulating gene expression in eukaryotes because …
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. Recall that the trp operon has a special leader sequence (trpL) between the operator and the structural genes that offers attenuation as a mechanism for regulation of gene expression.
(A) Draw a diagram of a trpL region of the operon when tryptophan is abundant in the cell.Label the following features: the DNA, 5’ and 3’ polarity of the RNA, the regions 1, 2, 3,and 4 and poly-U of the RNA, the pair of Trp codons (UGG), the ribosome, and RNA-Pol,along with any stem-loop structure that would form under these conditions
(B) In the above example, will the rest of the trp operon genes be expressed? Briefly describe your reasoning why or why not
(C) The trp codons in region 1 of the trpL gene have mutated to cysteines (UGG to UGC). What will be the effect on attenuation gene regulation of the trp operon? Brieflyexplain your reasoning.
Considering the Lac operon in E. coli, and chose what the expression of Lac Y would be in:
I) E. coli WT (wild type, everything is functional)
II) E. coli whose lacI gene has been deleted.
Each of the two strains is growing in culture flasks that contain high glucose and high lactose.
(choose among ‘high expression; low expression; no expression’)
Like the lac operon, the hexose operon is controlled by a separate regulatory protein under the control
of its own promoter (see the schematic of the operon below). The hexose regulatory protein is
sensitive to fatty acyl CoA levels. When all hexose fuel sources are depleted, the bacteria switch to
lipid metabolism and fatty acyl CoA levels increase. This turns expression of the hexose operon off.
+1
+1
Regulatory Gene
Pregulator
Poperon O
Hexose Operon Genes
regulator promoter
operon promoter
Chapter 20 Solutions
Becker's World of the Cell (9th Edition)
Ch. 20 - Suppose you are analyzing a haploid E. coli strain...Ch. 20 - How do epigenetic changes, such as DNA...Ch. 20 - Compare the basic state of a gene in bacteria...Ch. 20 - Prob. 1QCh. 20 - Prob. 20.4CCCh. 20 - Prob. 20.1PSCh. 20 - The Pickled Prokaryote. Pickelensia hypothetica is...Ch. 20 - Prob. 20.3PSCh. 20 - Attenuation in 25 or Fewer Words. Complete each of...Ch. 20 - Prob. 20.5PS
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- In the: Mutation of the regulatory region for a repressor protein in the lac operon. Explain: (a) What is the process affected? (b) What is the Effect on the process? (c) Does it affect prokaryotes, eukaryotes or both?arrow_forwardPredict the level of genetic activity of the lac operon as well as the status of the lac repressor and the CAP protein under the cellular conditions listed in the accompanying table. Lactose Glucose (a) - - (b) + - (c) - + (d) + +arrow_forwardAnswer as Directed. Below is the model of a lac operon. lac I lac Z с promoter operator lac Y lac A DNA +1 1. What are structural genes? Are the lac structural genes transcribed in the absence of lactose? 2. What is the role of the promoter and operator sites in the operon? 3. Is the repressor protein bound to the operator site in the absence of lactose? In its absence? 4. Under what nutritional circumstances (high or low glucose) is CAP bound to cAMP? 5. In the absence of lactose and the presence of glucose in the bacterial growth media, what proteins are bound to the lac control region? Is the operon being transcribed then? 6. In the presence of lactose and the presence of glucose in the bacterial growth media, what proteins are bound to the lac regulatory region? Is the operon being transcribed then? 7. In the presence of lactose and the absence of glucose in the bacterial growth media, what proteins are bound to the lac control region? 8. Why is it adaptive for a bacterium to not…arrow_forward
- Regulation of Genes and Their products 1. Given the following genotypes, explain how the mutation (identified by a (-) superscript) wil affect E. coll grown in lactose medium. Will the lac operon be on or off? Will there be a complete set of gene products from the lac operon? What will be the implication of the missing gene product, if ever? Will the cell be able to survive in the lactose medium or not? a. I+p+o+z- y+ b. i- p+o+z+y+ c. i+p+o- z+y+ d. i+p- o+z+y+ 2. In terms of the trp operon, differentiate between two normal bacterial cultures, one grown in a medium supplied with tryptophan and the other medium without tryptophan. 3. Experiments show that mutations at gene E lead to non-repressible transcription of trp genes. Why?arrow_forwardRead aloud V Draw Highlight 2. You are studying the regulation of the lactose operon in Escherichia coli, by measuring expression of the lacZ gene (i.e production of beta-galactosidase). (a) You identify several loss-of-function mutations in which lacZ is never expressed, in the presence and absence of glucose and lactose. What components of the lac operon could be mutated to produce this phenotype? List all possibilities. (b) You identify another loss-of-function mutation with the following expression pattern: Media + glucose - lactose + glucose +lactose - glucose - lactose - glucose + lactose lacZ expression Low Low High High What components of the lac operon could be mutated to produce this phenotype? List all possibilities.arrow_forwardIG-LA ED What pattern of functional protein synthesis of ß-galactosidase and permease, respectively, would you expect from an I*P*OCZ+Y+ lac operon in the absence of lactose? O ++ O -- O +- O+arrow_forward
- True or False. Explain. A) At no time during protein synthesis does an amino acid make direct contact with the mRNA being translated. B) Because the two strands of DNA are complementary, the mRNA of a gene can be synthesized using either strand as a template.arrow_forwardAnswer as Directed. Below is the model of a lac operon. lac I lac Z с promoter operator +1 lac Y lac A DNA 1. In the absence of lactose and the presence of glucose in the bacterial growth media, what proteins are bound to the lac control region? Is the operon being transcribed then? 2. In the presence of lactose and the presence of glucose in the bacterial growth media, what proteins are bound to the lac regulatory region? Is the operon being transcribed then? 3. In the presence of lactose and the absence of glucose in the bacterial growth media, what proteins are bound to the lac control region? 4. Why is it adaptive for a bacterium to not express the genes that encode for that lactose utilization proteins when lactose is not available or when glucose is present? 5. Why is it adaptive for the structural genes for using lactose to be under the control of a single promoter, i.e., synthesize a polycistronic message rather than three monocistronic message?arrow_forwardTrue/false? if false, justify brieflyBacterial operons gather open-reading-frames that are coupled for both transcription and translation.arrow_forward
- Explain why (a) inactivation of the O2 or O3 sequence of the lac operon causes only a twofold loss in repression, and (b) inactivation of both O2 and O3 reduces repression ∼70-fold.arrow_forwardAAAGAGAAAAGAAUA to AAAGAGAAAUGAAUA. Suppose the codon sequence has a single base pair mutation If the old protein sequence was Lys-Glu-Lys-Arg-Ile, what will be the new sequence encoded by the mutant gene? (Use the 3-letter amino acid abbreviations with hyphens and no spaces in between, i.e. Ser-Asn-Tyr-Leu-Pro.) Submit Answer Retry Entire Group No more group attempts remainarrow_forwardTranscription AttenuationHow would transcriptionof the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA?(a) Increasing the distance (number of bases) betweenthe leader peptide gene and sequence 2(b) Increasing the distance between sequences 2 and 3(c) Removing sequence 4(d) Changing the two Trp codons in the leader peptidegene to His codons(e) Eliminating the ribosome-binding site for the genethat encodes the leader peptide(f) Changing several nucleotides in sequence 3 so thatit can base-pair with sequence 4 but not with sequence 2arrow_forward
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