Function of CFTR protein in maintaining mucus concentration

• What happens where there is too little water in the mucus?

  1. Chlorine ion is pumped across the basal membrane into the cell
  2. Chlorine ion diffuses through the open CFTR channels into the mucus
  3. Sodium ion diffuses down the electrical gradient into the mucus
  4. Increases salt levels in mucus causes water to exit cell into mucus through osmosis
  5. Water is drawn into cell by osmosis
• What happens where there is excess water in the mucus?

  1. Sodium ion is actively pumped across the basal membrane out of the cell
  2. Sodium ions diffuse through the open Na channel from the apical membrane into the cell
  3. Chloride ions diffuse down the electrical gradient into the mucus
  4. Water is drawn out of cell by osmosis due to the high salt concentration in the tissue fluid
  5. Water is drawn out of the mucus by osmosis back into the cell
• What happens in a person with CF with a non functioning CFTR protein?

  1. CFTR channel is absent/ non functional
  2. Sodium channel is permanantly open
  3. Water is continually removed from mucus by osmosis making it sticky and leading to buildup in lungs
• What is the function of the CFTR channel protein?


  It transports chloride ions out of the cell into the mucus to reduce water levels in the mucus
• How can a mutation in the CFTR gene result in no protein being synthesised?


  It could change the order of bases hence there is no start codon. As a result, transcription can't occur so the protein can't be made
• Where is the CFTR protein found?

  Inside the cell membrane of mucus producing cells
• How could a change to the primary structure of the protein lead to it being misfolded?

  The change in primary structure is due to a change in the sequence of amino acids. This changes the hydrogen bonds leading to a different shape of protein
• How would a faulty opening of the CFTR protein affect its function?

  Since the CFTR protein is a channel protein, if its faulty, then chloride ions can't diffuse through hence less chloride ions would leave the cell
• Why is having small quantities of the CFTR protein bad?

  There will be less water in the mucus leading to it being thicker. As a result, the mucus can block the sperm duct or cervix, leading to fertility issues
• How is the CFTR protein broken down?

  By enzymes through hydrolysis of peptide bonds