4. Predict 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 following table (+ = sugar present; = sugar absent): Cellular conditions Lactose + b) Operon (on or off or basal?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?) d) Operon (on or off or basal?) Glucose + + a) Operon (on or off or basal?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?) c) Operon (on or off or basal?) PRE + Lac repressor (bound to operator?) CAP protein (bound to CAP site?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?)

4. Predict 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 following table (+ = sugar present; = sugar absent): Cellular conditions Lactose + b) Operon (on or off or basal?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?) d) Operon (on or off or basal?) Glucose + + a) Operon (on or off or basal?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?) c) Operon (on or off or basal?) PRE + Lac repressor (bound to operator?) CAP protein (bound to CAP site?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?)

Biology: The Dynamic Science (MindTap Course List)

4th Edition

ISBN:9781305389892

Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Publisher:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter16: Regulation Of Gene Expression

Section: Chapter Questions

Problem 2TYK: For the E. coli lac operon, when lactose is present: a. and glucose is absent, cAMP binds and...

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For the E. coli lac operon, when lactose is present: a. and glucose is absent, cAMP binds and activates catabolicactivator protein (CAP). b. and glucose is absent, the level of cAMP decreases. c. activated CAP binds the repressor protein to remove it from the operator gene. d. the cell prefers lactose over glucose. e. RNA polymerase cannot bind to the promoter.
INTERPRET DATA Develop a simple hypothesis that would explain the behavior of each of the following types of mutants in E. coli. Mutant a: The map position of this mutation is in the trp operon. The mutant cells are constitutive; that is, they produce all the enzymes coded for by the trp operon, even if large amounts of tryptophan are present in the growth medium. Mutant b: The map position of this mutation is in the trp operon. The mutant cells do not produce any enzymes coded for by the trp operon under any conditions. Mutant c: The map position of this mutation is some distance from the trp operon. The mutant cells are constitutive; that is, they produce all the enzymes coded for by the trp operon, even if the growth medium contains large amounts of tryptophan.
4. Predict 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 following table (+ = sugar present; -= sugar absent): Cellular conditions Lactose + b) Operon (on or off or basal?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?) d) Operon (on or off or basal?) Glucose + + a) Operon (on or off or basal?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?) c) Operon (on or off or basal?) TDOO + Lac repressor (bound to operator?) CAP protein (bound to CAP site?) Lac repressor (bound to operator?) CAP protein (bound to CAP site?)
1. The table below shows partial diploid E. coli with lac operon mutations For each mutant, indicate whether expression of permease is:• None (absent)• Basal (on but low expression)• High (on and activated expression)when grown in either lactose only or glucose only media. Also indicate the cell’s overall growth phenotype (lac+ or lac-) when grown in lactose only and why you expect that phenotype (provide “why” for ONLY THREE of the mutants). ***Recall that a bacterial cell needs at least one functional copy of lacZ AND lacY expressed at high levels to producean overall growth phenotype of lac+ when grown in lactose only media. Lac Mutant CAP bindingsite Expression inlactose only Expression inglucose only Phenotype in lactose only I+ P+ O+ Z- Y+ / I- P+ O+ Z+ Y- WT Why?: Why?: Why?: Why?: Why?: I+ P+ O+ Z- Y- / I+ P- O+ Z+ Y+ WT Why?: Why?: Why?: Why?: Why?: I+ P+ O+ Z- Y+ / I+ P+ OC Z- Y+ WT Why?: Why?: Why?: Why?: Why?: IS P+ O+ Z+ Y- / I- P+ O+ Z+…
1. Draw a diagram of the lac operon. PO I+P+O+Z+Y+ I+P+OcZ+Y- I-P+O+Z+Y+ Lab section (circle): lacz gene lac Y gene lacA gene I+P+O+ZY/IPO+Z+Y- 2. The promoter (P) is the start site of transcription through the binding of RNA polymerase before actual mRNA production. Mutated promoters (P) cannot bind RNA polymerase, so no mRNA is made. In the table below, make predictions about the expression of ß-galactosidase and permease for different partial diploid (F') genotypes. Do this for E. coli growth on two different types of media - one without lactose, and one with. Use a to mark where there is no enzyme produced, and a + to mark where the enzyme is made. The first genotype has all wild-type alleles, and has been filled in as an example. Genotype IPOCZ+Y/I-P+O+Z-Y+ ISP+O+Z+Y/I+P+O+Z*Y* CR 1:00 Lactose absent B-galactosidase Permease R 3:-00 + R 6:30 Lactose present B-galactosidase F 10:00 Permease
. 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.
Answer this 3 part question: (MC) What is the function of lactose in regulation of the lac operon? 1. activates a repressor protein 2. activates an activator protein 3. inactivates a repressor protein 4. inactivates an activator protein Consider a bacterial strain with a lac operon Р. О Y A a) Mention which parts of the DNA region shown in the diagram encode for • Enzyme proteins? • Operator • Promoter • Repressor gene b) Where would the lac repressor be bound in a E. coli cell that is growing in ( • high lactose? No lactose
4) Suppose you have an E. coli in which the gene that codes for the lac repressor protein has been mutated in such a way that the protein produced can bind to both lactose and DNA (at its specific binding site in the lac operon promoter) simultaneously. What effect, if any, would this have on regulation of expression of the lac operon? Briefly (1 sentence) explain why you would predict the effect or lack of effect this mutation would have.
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 K
Read 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.
2. The lac operon controls the inducible expression of genes involved in lactose utilization. Several naturally occurring mutations have been discovered that affect how the lac operon operates. Consider the following mutations: I-= a mutation in the repressor protein that cannot bind the operator Is = a mutation in the repressor protein that cannot be removed from the operator Oc= a mutation in the operator that cannot bind the repressor Detail the functionality of the lac operon with following genotypes and cellular conditions (Note if there is no superscript, there is no mutation) Genotype I, O I, OC IS, O I, O Is, Oc Lactose present No No Yes Yes No Repressed (yes/no) N VAS ves NO Constitutive (yes/no) NO NO YES Yes NO Inducible (yes/no) Yes yes NO NO YUS
Interpret the level of gene expression of the lac operon, as well as the status of the lac repressor and the CAP protein, when bacterial growth media contain the following sugar: (1) Lactose but no glucose. (ii) Glucose and no lactose.