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Carrying the Cystic Fibrosis Allele Offer Protection from Typhoid Fever Epithelial cells that lack the CFTR protein cannot take up bacteria by endocytosis. Endocytosis is an important part of the respiratory tract’s immune defenses against common Pseudomonas bacteria, which is why Pseudomonas infections of the lungs are a chronic problem in cystic fibrosis patients. Endocytosis is also the way that Salmonella typhi bacteria (shown at right) enter cells of the gastrointestinal tract, where internalization of this bacteria can result in typhoid fever. Typhoid fever is a common worldwide disease. Its symptoms include extreme fever and diarrhea, and the resulting dehydration causes delirium that may last several weeks. If untreated it kills up to 30 percent of those infected. Around 600,000 people, most of whom are children, die annually from typhoid fever. Gerald Pier and his colleagues compared the uptake of S. typhi by different types of epithelial cells: those homozygous for the normal allele, and those heterozygous for the ΔF508 allele associated with CF. (Cells that are homozygous for the mutation do not take up any S. typhi bacteria .) Some of their results are shown in FIGURE 13.16 . FIGURE 13.16 Effect of the ΔF508 mutation on the uptake of three different strains of Salmonella typhi bacteria by epithelial cells. Entry of all three S. typhi strains into the heterozygous epithelial cell was inhibited. Is it possible to tell from this graph which strain was most inhibited?

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Biology: The Unity and Diversity o...

15th Edition
Cecie Starr + 3 others
Publisher: Cengage Learning
ISBN: 9781337408332

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Chapter
Section
BuyFindarrow_forward

Biology: The Unity and Diversity o...

15th Edition
Cecie Starr + 3 others
Publisher: Cengage Learning
ISBN: 9781337408332
Chapter 13, Problem 3DAA
Textbook Problem
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Carrying the Cystic Fibrosis Allele Offer Protection from Typhoid Fever Epithelial cells that lack the CFTR protein cannot take up bacteria by endocytosis. Endocytosis is an important part of the respiratory tract’s immune defenses against common Pseudomonas bacteria, which is why Pseudomonas infections of the lungs are a chronic problem in cystic fibrosis patients. Endocytosis is also the way that Salmonella typhi bacteria (shown at right) enter cells of the gastrointestinal tract, where internalization of this bacteria can result in typhoid fever.

Typhoid fever is a common worldwide disease. Its symptoms include extreme fever and diarrhea, and the resulting dehydration causes delirium that may last several weeks. If untreated it kills up to 30 percent of those infected. Around 600,000 people, most of whom are children, die annually from typhoid fever.

Gerald Pier and his colleagues compared the uptake of S. typhi by different types of epithelial cells: those homozygous for the normal allele, and those heterozygous for the ΔF508 allele associated with CF. (Cells that are homozygous for the mutation do not take up any S. typhi bacteria.) Some of their results are shown in FIGURE 13.16.

Chapter 13, Problem 3DAA, Carrying the Cystic Fibrosis Allele Offer Protection from Typhoid Fever Epithelial cells that lack , example  1

Chapter 13, Problem 3DAA, Carrying the Cystic Fibrosis Allele Offer Protection from Typhoid Fever Epithelial cells that lack , example  2

FIGURE 13.16 Effect of the ΔF508 mutation on the uptake of three different strains of Salmonella typhi bacteria by epithelial cells.

Entry of all three S. typhi strains into the heterozygous epithelial cell was inhibited. Is it possible to tell from this graph which strain was most inhibited?

Summary Introduction

To explain: The strain of Salmonella typhi that was inhibited most by CFTR mutation.

Concept introduction: Allele is the modification of the gene. Salmonella typhi is the causative bacteria of typhoid. Cystic fibrosis (CF) is a genetic disorder due to inability of the cell to perform endocytosis due to mutation in the CFTR gene. Cystic fibrosis affects the lungs, intestine, liver, and kidneys. Endocytosis is a phenomenon where the cell takes up molecules by engulfing with its membrane. The S. typhi exploits this mechanism to infect the intestinal cell and cause diarrhea. The cells that are homozygous for this CFTR mutation cannot perform endocytosis, and the S. typhi cannot infect those individuals.

Explanation of Solution

Scientist G with his colleagues studied the uptake of S. typhi by two types of epithelial cells:

  • Cells that are homozygous for the normal allele
  • Cells that are heterozygous for ΔF508 allele associated with CF and normal allele

Cells that are homozygous for the mutant allele do not take up S. typhi; therefore, those cells were not chosen. A bar graph was drawn with three strains of S. typhi on the X-axis, and the number of bacteria internalized by both types of cells in the Y-axis.

Approximately, 600,000 Ty2 strains of S. typhi entered the normal cells that are homozygous for the normal allele.

Approximately, 80,000 Ty2 strains of S. typhi entered the mutated cells that are heterozygous for ΔF508 allele associated with CF and normal allele.

Therefore, the number of times more S. typhi entered normal cells than heterozygous cells =60000080000=7.5

Approximately, 75,000 of strain 167 of S. typhi entered the normal cells that are homozygous for the normal allele

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