How Hemorrhagic E. coliResists the Acid Environmentof the StomachpH Sensitivity of the Glu-GABA Antiporter300GadCRecent years have been marked by a series of foodpoisoning outbre aks involving hemorrhagic (producinginternal bleeding) strains of the bacterium Escherichia coli(E. coli). Bacteria are often a source of food poisoning,typically milder infections caused by food-borne strepto-coccal bacteria. Less able to bear the extremely acidicconditions encountered by food in the human stomach(pH 2), E. coli has not been as common a problem. Thehemorrhagic strains of E. coli responsible for recent out-breaks seem to have evolved more elaborate acid-resistanceAdiC25020015010050-65systems.How do hemorrhagic E. coli bacteria survive in theacid environment of the stomach? The problem they face,pHin essence, is that theyions. many of which diffuse into their cells. To rid them-selves of these excess hydrogen ions, the E. coli cells use aclever system to pump hydrogen ions back out of theirsubmerged in a sea of hydrogenareAnalysis1. Applying Conceptsa. Variable. In the graph, what is the dependentvariable?cells.First, the hemorrhagic E. coli cells take up cellularhydrogen ions by using the enzyme glutamic acid decarbox-vlase (GAD) to convert the amino acid glutamate toy-aminobutyric acid (GABA), a decarboxylation reaction thatconsumes a hydrogen ion.Second, the hemorrhagic E. coli export this GABAfrom their cell cytoplasm using a Glu-GABA antiportercalled GadC (this transmembrane protein channel is calledan antiporter because it transports two molecules across themembrane in opposite directions).However, to survive elsewhere in the human body, itis important that the Glu-GABA antiporter of hemorrhagicE. coli not function, lest it short-circuit metabolism. To see ifthe GadC antiporter indeed functions only in acid environ-ments, investigators compared its activity at a variety of pHswith that of a different amino acid antiporter called AdiC,which transports arginine out of cells under a broadrange of conditions. The results of monitoring transport for10 minutes are presented in the graph.b. Substrate. What is a substrate? In thisinvestigation, what are the substrates that areaccumulating?c. pH. What is the difference in hydrogenion concentration between pH 5 and pH 7?How many times more (or less) is that? Explain.2. Interpreting Dataa. Does the amount of amino acid transportedin the 10-minute experimental interval(expressed as substrate accumulation) varywith pH for the arginine-transporting AdiCantiporter? For the glutamate-transportingGadC antiporter?b. Compare the amount of substrate accumulatedby AdiC in 10 minutes at pH 9.0 with thataccumulated at pH 5.0. What fraction of thelow pH activity is observed at the higher pH?c. In a similar fashion, compare the amount ofsubstrate accumulated by GadC at pH 9.0with that accumulated at pH 5.0. Whatfraction of the low pH activity is observed atthe higher pH?3. Making Inferences Would you say that the GadCantiporter exhibits the same pH dependence as theAdiC antiporter? If not, which antiporter is lessactive at nonacid pHs?4. Drawing Conclusions Is the glutamate-GABAantiporter GadC active at nonacid pHs?5. Further Analysis The GadC antiporter alsotransports the amino acid glutamine (Gln). Do youthink this activity has any role to play in combatinglow pH environments? How would you test thishypothesis?OutsideInsidecellcellGABAGlutamateChapter 5 Membranes 111Substrate accumulation(nmol per mg protein)-00Inquiry & Analysis

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Asked Sep 6, 2019
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Number 4 I would say yes. Am I right? 

How Hemorrhagic E. coli
Resists the Acid Environment
of the Stomach
pH Sensitivity of the Glu-GABA Antiporter
300
GadC
Recent years have been marked by a series of food
poisoning outbre aks involving hemorrhagic (producing
internal bleeding) strains of the bacterium Escherichia coli
(E. coli). Bacteria are often a source of food poisoning,
typically milder infections caused by food-borne strepto-
coccal bacteria. Less able to bear the extremely acidic
conditions encountered by food in the human stomach
(pH 2), E. coli has not been as common a problem. The
hemorrhagic strains of E. coli responsible for recent out-
breaks seem to have evolved more elaborate acid-resistance
AdiC
250
200
150
100
50-
6
5
systems.
How do hemorrhagic E. coli bacteria survive in the
acid environment of the stomach? The problem they face,
pH
in essence, is that they
ions. many of which diffuse into their cells. To rid them-
selves of these excess hydrogen ions, the E. coli cells use a
clever system to pump hydrogen ions back out of their
submerged in a sea of hydrogen
are
Analysis
1. Applying Concepts
a. Variable. In the graph, what is the dependent
variable?
cells.
First, the hemorrhagic E. coli cells take up cellular
hydrogen ions by using the enzyme glutamic acid decarbox-
vlase (GAD) to convert the amino acid glutamate to
y-aminobutyric acid (GABA), a decarboxylation reaction that
consumes a hydrogen ion.
Second, the hemorrhagic E. coli export this GABA
from their cell cytoplasm using a Glu-GABA antiporter
called GadC (this transmembrane protein channel is called
an antiporter because it transports two molecules across the
membrane in opposite directions).
However, to survive elsewhere in the human body, it
is important that the Glu-GABA antiporter of hemorrhagic
E. coli not function, lest it short-circuit metabolism. To see if
the GadC antiporter indeed functions only in acid environ-
ments, investigators compared its activity at a variety of pHs
with that of a different amino acid antiporter called AdiC,
which transports arginine out of cells under a broad
range of conditions. The results of monitoring transport for
10 minutes are presented in the graph.
b. Substrate. What is a substrate? In this
investigation, what are the substrates that are
accumulating?
c. pH. What is the difference in hydrogen
ion concentration between pH 5 and pH 7?
How many times more (or less) is that? Explain.
2. Interpreting Data
a. Does the amount of amino acid transported
in the 10-minute experimental interval
(expressed as substrate accumulation) vary
with pH for the arginine-transporting AdiC
antiporter? For the glutamate-transporting
GadC antiporter?
b. Compare the amount of substrate accumulated
by AdiC in 10 minutes at pH 9.0 with that
accumulated at pH 5.0. What fraction of the
low pH activity is observed at the higher pH?
c. In a similar fashion, compare the amount of
substrate accumulated by GadC at pH 9.0
with that accumulated at pH 5.0. What
fraction of the low pH activity is observed at
the higher pH?
3. Making Inferences Would you say that the GadC
antiporter exhibits the same pH dependence as the
AdiC antiporter? If not, which antiporter is less
active at nonacid pHs?
4. Drawing Conclusions Is the glutamate-GABA
antiporter GadC active at nonacid pHs?
5. Further Analysis The GadC antiporter also
transports the amino acid glutamine (Gln). Do you
think this activity has any role to play in combating
low pH environments? How would you test this
hypothesis?
Outside
Inside
cell
cell
GABA
Glutamate
Chapter 5 Membranes 111
Substrate accumulation
(nmol per mg protein)
-00
Inquiry & Analysis
help_outline

Image Transcriptionclose

How Hemorrhagic E. coli Resists the Acid Environment of the Stomach pH Sensitivity of the Glu-GABA Antiporter 300 GadC Recent years have been marked by a series of food poisoning outbre aks involving hemorrhagic (producing internal bleeding) strains of the bacterium Escherichia coli (E. coli). Bacteria are often a source of food poisoning, typically milder infections caused by food-borne strepto- coccal bacteria. Less able to bear the extremely acidic conditions encountered by food in the human stomach (pH 2), E. coli has not been as common a problem. The hemorrhagic strains of E. coli responsible for recent out- breaks seem to have evolved more elaborate acid-resistance AdiC 250 200 150 100 50- 6 5 systems. How do hemorrhagic E. coli bacteria survive in the acid environment of the stomach? The problem they face, pH in essence, is that they ions. many of which diffuse into their cells. To rid them- selves of these excess hydrogen ions, the E. coli cells use a clever system to pump hydrogen ions back out of their submerged in a sea of hydrogen are Analysis 1. Applying Concepts a. Variable. In the graph, what is the dependent variable? cells. First, the hemorrhagic E. coli cells take up cellular hydrogen ions by using the enzyme glutamic acid decarbox- vlase (GAD) to convert the amino acid glutamate to y-aminobutyric acid (GABA), a decarboxylation reaction that consumes a hydrogen ion. Second, the hemorrhagic E. coli export this GABA from their cell cytoplasm using a Glu-GABA antiporter called GadC (this transmembrane protein channel is called an antiporter because it transports two molecules across the membrane in opposite directions). However, to survive elsewhere in the human body, it is important that the Glu-GABA antiporter of hemorrhagic E. coli not function, lest it short-circuit metabolism. To see if the GadC antiporter indeed functions only in acid environ- ments, investigators compared its activity at a variety of pHs with that of a different amino acid antiporter called AdiC, which transports arginine out of cells under a broad range of conditions. The results of monitoring transport for 10 minutes are presented in the graph. b. Substrate. What is a substrate? In this investigation, what are the substrates that are accumulating? c. pH. What is the difference in hydrogen ion concentration between pH 5 and pH 7? How many times more (or less) is that? Explain. 2. Interpreting Data a. Does the amount of amino acid transported in the 10-minute experimental interval (expressed as substrate accumulation) vary with pH for the arginine-transporting AdiC antiporter? For the glutamate-transporting GadC antiporter? b. Compare the amount of substrate accumulated by AdiC in 10 minutes at pH 9.0 with that accumulated at pH 5.0. What fraction of the low pH activity is observed at the higher pH? c. In a similar fashion, compare the amount of substrate accumulated by GadC at pH 9.0 with that accumulated at pH 5.0. What fraction of the low pH activity is observed at the higher pH? 3. Making Inferences Would you say that the GadC antiporter exhibits the same pH dependence as the AdiC antiporter? If not, which antiporter is less active at nonacid pHs? 4. Drawing Conclusions Is the glutamate-GABA antiporter GadC active at nonacid pHs? 5. Further Analysis The GadC antiporter also transports the amino acid glutamine (Gln). Do you think this activity has any role to play in combating low pH environments? How would you test this hypothesis? Outside Inside cell cell GABA Glutamate Chapter 5 Membranes 111 Substrate accumulation (nmol per mg protein) -00 Inquiry & Analysis

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Expert Answer

Step 1

Escherichia coli abbreviated as E. Coli is a bacterium commonly found in the digestive system of warm-blooded organisms. It helps in the process of digestion. Although most of the strains of E. coli are not harmful, some strains like the hemorrhagic strain can cause internal bleeding in the stomach.

Step 2

General strains of E. coli are not able to cause them harm, due to the acidic medium in the stomach. Whereas, in the case of hemorrhagic E. coli, they have a specialized mechanism that makes them resistant towards the low pH and keeps them unaffected.

Even though they live in a highly acidic environment they have an amazing resi...

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