Chapter 5, Problem 1TC

Summary Introduction

To explain:

The reason that why the defective protein results in a thick sticky mucous outside the cells rather than a loose fluid covering in cystic fibrosis genetic disorder.

Introduction:

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is expressed when an individual inherits a pair of the recessive allele of the cystic fibrosis gene. This gene then expresses and translates into nonfunctional proteins (cystic fibrosis). This protein then forms a transmembrane conductance regulator which forms the chlorine channels that surrounds the membranes, which produce mucus, sweat and tears. Any mutation in genes of CFTR cause the cystic fibrosis disorder and affect the transmembrane protein functioning.

Explanation of Solution

Chlorine channels present on the cell membrane are necessary for the transport of chloride ions that helps in the water movement which is essential for the production of mucus. Mucous is a mixture of water and glycoproteins. The balance between water and volume of mucous is maintained by the release and absorption of ions and water across the cell membrane. This mucus protects the epithelial lining of lungs and digestive system from any infections.

But in a genetic disorder cystic fibrosis, improper folding of the cystic fibrosis proteins affects the functioning of the chlorine channels which prevents the efflux of chloride ions outside the cell. Thus, chlorine ions are accumulated inside the cells that results in less water movement outside and formation of mucous outside the cell. Due to closure of channels, the water movement outside the cell is prevented and the water content of mucous decreases. This results in more thick and sticky mucus accumulation instead of fluid outside the cell. This causes entrapment of bacteria as the cilia of epithelial cells are unable to remove excess mucous from the surrounding of cell. This causes the chronic respiratory infections.

Conclusion

The prevention of efflux of chloride ions outside the cell disturbs the balance between water and mucous volume as water does not leave cells and causes more thick mucus formation instead of fluid.