After reading the paragraphs below, answer the questions that follow.
Cystic fibrosis is an autosomal recessive genetic disorder that most severely affects the lungs and respiratory tract. Cystic fibrosis is caused by a mutation in the gene for the protein cystic fibrosis transmembrane regulator (CFTR), which regulates the movement of chloride and sodium ions across epithelial cell membranes. When the CFTR gene is mutated in cystic fibrosis, the defective CFTR protein cannot transport ions properly, which results in too little water drawn across the membrane and the buildup of thick and sticky (viscous) mucus, especially in the airways. This leads to difficulty of breathing, frequent lung infections, and ultimately death.
Research has shown that some of the increased thickness and viscosity of the mucus in the respiratory tract is due to the presence of human DNA. If DNA is present in high concentrations in solution, the DNA molecules can get entangled and lead to a thick, viscous solution. To combat this, pharmaceutical companies have developed recombinant forms of the human deoxyribonuclease I (DNase I) protein. DNase I, after being translated and modified with sugar groups, is normally produced in human cells and possibly plays a role in DNA breakdown during apoptosis (programmed cell death).
If recombinant DNase I is added to a vial of respiratory secretions from a cystic fibrosis patient, which of the following results would indicate that the recombinant DNase I is functional?
◦ The secretions become less viscous.
◦ There is no effect on the secretions.
◦ The secretions become thicker and more viscous.
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