Q21. What regulators of gene expression bind the lac promoter region if E. coli is grown in media containing lactose but not glucose? The lacl repressor doesn't bind, but the CAP protein does. Neither the lacl repressor nor the CAP protein bind. Both the lacl repressor and the CAP protein bind. The lacl repressor binds, but the CAP protein doesn't.
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- E27. A cloned gene fragment contains a regulatory element that is recog- nized by a regulatory transcription factor. Previous experiments have shown that the presence of a hormone results in transcriptional acti- vation by this transcription factor. To study this effect, you conduct a electrophoretic mobility shift assay and obtain the following results: Tube: 1 2 3 Transcription factor: Hormone: Explain the action of the hormone.Match the term with its description. cAMP Allows lactose to enter the cell and product of the lacY gene A regulatory sequence between the promoter and the structural genes of the lac operon When glucose levels are high, intracellular levels of this molecule are low Binds to and inhibits the function of the lac repressor when lactose is presentAnswer 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…
- A. A mutation is recovered in the gene that encodes the lactose operon repressor protein (LacI). Which of the following lac phenotypes would lead to the conclusion that the mutation causes an inability of the repressor to bind lactose? The lac structural genes would never be expressed. The lac structural genes would be expressed continuously. The lac structural genes would be expressed efficiently only in the absence of lactose. The lac structural genes would be expressed efficiently only in the presence of lactose. B. A mutation is recovered in the gene that encodes the lactose operon repressor protein (LacI). Which of the following lac phenotypes would lead to the conclusion that the mutation causes an inability of the repressor to bind Operator DNA? The lac genes would be expressed efficiently only in the presence of lactose. The lac genes would be expressed efficiently only in the absence of lactose. The lac genes would never be expressed. The lac genes would be…m.. In the figure below, the bacterial activator protein CAP and the Lac repressor have been placed in the four possible combinations on their binding sites in the promoter for the Lac operon. Each combination of gene regulatory proteins corresponds to a particular mixture of glucose and lactose. For each of the four combinations, indicate on the left-hand side of the figure which sugars must be present and, on the right-hand side, whether the operon is expected to be turned on or off. RNA- polymerase- start site for RNA synthesis CAP- binding binding site site (promoter) operator Lacz gene GLUCOSE LACTOSE OPERON ACTIVITY Lac repressor CAP Lac repressor CAP 60 40 40 80 nucieatide pairsE30. An electrophoretic mobility shift assay can be used to study the binding of proteins to a segment of DNA. In the experiment shown here, an EMSA was used to examine the requirements for the bind- ing of RNA polymerase II (from eukaryotic cells) to the promoter of a protein-encoding gene. The assembly of general transcription factors and RNA polymerase II at the core promoter is described in Chapter 12 (Figure 12.14). In this experiment, the segment of DNA containing a promoter sequence was 1100 bp in length. The fragment was mixed with various combinations of proteins and then subjected to an EMSA. Lane 1: No proteins added Lane 2: TFID Lane 3: TFIIB Lane 4: RNA polymerase I| Lane 5: TFID + TFIIB Lane 6: TFID + RNA 1 2 4 5 6 polymerase II| Lane 7: TFIID + TFIIB + RNA polymerase I| 1100 bp Explain which proteins (TFIID, TFIIB, or RNA polymerase II) are able to bind to this DNA fragment by themselves. Which transcrip- tion factors (i.e., TFIID or TFIIB) are needed for the binding of…
- Ⓒ Macmillan Learning Classify the given examples of prokaryotic gene expression as positive or negative gene regulation. 54 $ R In the presence of excess tryptophan, a repressor protein binds the operator of the trp operon and prevents the operon from being transcribed. In the absence of lactose, the lacR repressor protein binds the lac operon. F4 Positive gene regulation In the presence of the sugar arabinose, an activator protein binds the promoter of the genes responsible for processing arabinose and induces their transcription. In the presence of iron, the dtxR repressor protein binds DNA, and the gene that encodes for the diphtheria toxin is not expressed. % 5 In the presence of lactose and low glucose, the lac operon expressed 20-fold higher than in the absence of lactose. T F5 < 6 MacBook Air MA F6 Answer Bank & 7 F7 Y U * 8 DII F8 Negative gene regulation 1 ( 9 F9 O ) - C J F10 | ! LICPlz answer ASAP. I will thumb up 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.MATCH THE FF. WITH THE CHOICES BELOW group of genes one long mRNA with complementary codes of 3 or more genes controlled by negative regulation a tetrameric protein, is the lacI gene product It is a palindromic DNA segment at the upstream region of lac gene has a DNA-binding domain on N-terminus; the C-terminus binds inducer, forms tetramer. an accessory protein to activate transcription regulated both positively and negatively by AraC regulatory elements of arabinose operon It is Regulated Through a Co-Repressor-Mediated Negative Control Circuit an example of autogenous regulation has attenuation regulation mechanism CHOICES: -lac operator -Catabolite activator protein -araBAD Operon -polycistronic mRNA -trp Operon -lac operon -lac repressor -Operon -AraC gene
- . 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.12a. In what condition is the LacZ gene transcribed? ANSWER (in one sentence) 12b. Fill in the following table about the Lac operon (LacZ gene) Environmental Condition + Glucose and + Lactose Glucose and + Lactose - Glucose and - Lactose + Glucose and - Lactose Q 2 Body" W #3 E D Which proteins bind to the LacZ promoter? ANSWER ANSWER ANSWER ANSWER $ 4 A R F B % 5 I T MacBook Pro A U 6 G Y & 7 H Is LacZ transcribed? (Yes or No) ANSWER ANSWER ANSWER ANSWER |||| U 8 KRead 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.
