BIOCHEM 3000 Molecular And Structural Biology III

Cystic fibrosis is a multiple system disease affecting the lung, reproductive tract, digestive system, and sweat glands. It is a recessive genetic condition caused by a mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene that is regulated by cAMP (cyclic adenosine monophosphate). Three DNA bases deleted from the CFTR gene result in the loss of phenylalanine residue at AA position 508 (Kerem, 1989).

This gene codes instruction for the protein Cystic Fibrosis Transmembrane Conductance Regulator (CFTR).This protein usually acts as a transport medium across the membrane of cells responsible for the production of sweat, digestive enzymes, mucus, and saliva. Chloride ions transported within the cells control the movement of water in tissues hence influencing the thinning and the free flow of mucus.

The amino acid missing in the CFTR protein channel affect the CFTR chloride channel hence no water or chloride ions can flow in and out of the cells. As a result, the secreted mucus will be sticky and thick leading to obstruction of the airways, in turn, the symptoms of cystic fibrosis coughing and breathing difficulties. The defective CFTR leads to decreased chloride secretions and increased sodium reabsorption across the epithelial cells. Once the periciliary liquid is depleted, and mucus adheres to airways expanding the flow of mucus forming plugs which induce bacterial infection (Boucher, 2004). Besides, hypoxia promotes bacterial infection. Reduced epithelial lining decreases hydration of mucus making it sticker to bacteria hence increasing chances of infection and inflammation. The exocrine tissues have increased viscosity making them difficult to clear. Mucus clogs the pancreas thus stopping enzymes from reaching food in the gut leading to problems in the digestive system.

 Cystic fibrosis occurs upon mutation of the CFTR that leads to the absence of protein synthesis and then maturation of the defective protein. There is reduced ATP binding and hydrolysis the chloride channels reduce. The abnormality leads to decreased transcription and an accelerated turn over from the cell surface hence an increase in the secretions.

References

Boucher, R. C. (2004). New concepts of the pathogenesis of cystic fibrosis lung disease. European Respiratory Journal, 23(1), 146-158.

Kerem, B. S., Rommens, J. M., Buchanan, J. A., Markiewicz, D., Cox, T. K., Chakravarti, A., ... & Tsui, L. C. (1989). Identification of the cystic fibrosis gene: genetic analysis. Science, 245(4922), 1073-1080.