Cystic Fibrosis ( Genetic Technology) Biology

Cystic Fibrosis:

Cystic fibrosis is a genetic disorder in which abnormally thick mucus is produced in the lungs and other parts of the body. A person with cystic fibrosis is very prone to bacterial infections in the lungs because it is difficult for the mucus to be removed, allowing bacteria to bread in it. People with cystic fibrosis need daily therapy to help them to cough up this mucus. The thick mucus adversely affects many other parts of the body. The pancreatic duct may become blocked, and people with cystic fibrosis often take pancreatic enzymes by mouth to help with digestion. Around 90% of men with cystic fibrosis are sterile because thick secretions block ducts in the reproductive system.
Cystic fibrosis is caused by a recessive allele of the gene that codes for a transporter protein called CFTR. This protein sits in the cell surface membranes of cells in the alveoli and allows chloride ions to pass out of the cells. The recessive allele codes for a faulty version of this protein that does not act properly as a chloride ion transporter.

Normally, the cells lining the airways and in the lungs pump out chloride ions (Cl¯ )  through the channel in the cell surface membrane formed by CFTR. This results in a relatively high concentration of chloride ions outside the cells. This reduces the water potential below that of the cytoplasm of the cells. So water moves out of the cells by osmosis, down the water potential gradient. It mixes with the mucus there, making it thin enough for easy removal by the sweeping movements of cilia.

However, in someone with cystic fibrosis, much less water moves out of the cells, so the mucus on their surfaces stays thick and sticky. The cilia or even coughing can't remove it all.

Genetic Technology:

Gene technology is a procedure by which one or more selected genes are removed from one organism and inserted into another which is then said to be transgenic. Genetic technology can provide benefits in, for example, agriculture and medicine, but has the associated risk of the escape of the gene concerned into organisms other than the intended host. The risk is seen to be particularly high for genetically modified crops that are released into the environment to grow. 

The social implications of genetic technology are the benefits or otherwise effects of the technology on human societies. Ethics are sets of standards by which a particular group of people agrees to regulate their behavior, distinguishing an acceptable from an unacceptable activity. Each group must decide, first, whether research into gene technology is acceptable, and then whether or not it is acceptable to adopt the successful technologies.

Q.1. Different enzymes are used in the various steps involved in the production of bacteria capable of synthesizing a human protein. Which step is catalyzed by a restriction enzyme?

Ans: cutting open a plasmid vector

Q2. What describes a promoter?

Ans: a length of DNA that controls the expression of a gene

Q.3. Which statement correctly describes the electrophoresis of DNA fragments?

Ans: smaller fragments of DNA move more rapidly than larger fragments

Q.4. The figure shows the CFTR (cystic fibrosis transmembrane conductance regulator) protein in a cell surface membrane.

a) i) Describe the normal function of the CFTR protein.

ii) Use the letter E to indicate the external face of the membrane. State how you identified this face.

The CFTR gene is found on chromosome 7 and consists of about 250,000 bases. Mutations in this gene have produced several different defective alleles. The commonest of these is the result of a deletion of three bases. The CFTR protein made using the code on this allele is therefore missing one amino acid. The machinery in the cell recognizes that this is not the right protein and does not place it in the cell surface membrane.

Because the faulty CFTR alleles are recessive, someone with one faulty allele and one normal allele is able to make enough of the CFTR protein to remain healthy. The person is a symptom-free carrier of the disease. Each time two heterozygous people have a child, there is a one in four chance that their child will have the disease.

More recently, a different approach has been taken. In some people with cystic fibrosis, the mutation in the gene has simply replaced one base with another. This has created a 'stop' codon in the middle of the gene. The gene is transcribed in the normal way, but translation on the ribosomes stops when this codon is reached. This means that only a short length of the CFTR protein is made. A drug called PTC124 has been found to allow translation to just keep going across this stop codon, so the entire protein is made albeit with -a wrong or missing amino acid in the middle of it. Clinical trials have shown hopeful signs that this may allow enough CFTR to be made to significantly relieve the symptoms of some people with cystic fibrosis.  It is much easier to do than 'classic' gene therapy because it only involves the patient taking a pill each day.

AQA-2018:

Q.6. Cystic fibrosis(CF) is a genetic disorder caused by a change in a gene.

6.1. What molecule are genes made of?

Ans: DNA

6.2. CF affects the cell membranes of cells in the lungs and digestive system.

What is the function of cell membrane?

Ans: The cell membrane controls the movement of substances in or out of the cell.

6.3.  In a person with CF, cells lining the lungs and digestive system create too much mucus. 

The mucus can:

* block the duct leading from the pancreas to the small intestine.

* block the tubes leading to the alveoli in lungs.

Explain why children with CF grow more slowly than children without CF.

Ans: 1. Fewer enzymes enter the small intestine.

2. Less absorption of nutrients.

3. Less glucose can enter the blood.

4. Fewer amino acids can enter the blood.

5. Less available for respiration.

6. Less oxygen enters the blood.

Table 6 shows information about people in the UK in 2015.

TABLE   6                           Median age in years

People with CF                        19

Whole population                    40

6.4. Describe how the median age of a group of people can be determined.

Ans: *Put ages in ascending order

            *Find middle value.   

6.5. Suggest ONE reason why the median age for people with CF is lower than the median age for the whole population.

Ans: The median age for people with CF is lower than the median age for the whole population because most common in young people.        

6.6. People with a lung function below 30% may need a lung transplant. TABLE 7 gives information about people with CF in 2015.

TABLE 7

Lung function (%)                                                  Percentage of people with CF

75                                                                                  22

51 - 75                                                                           72

30- 50                                                                              4

30                                                                                     2          

In 2015, the total number of people with CF in the UK was 10800.

Calculate how many people with CF in the UK in 2015 would NOT need a lung transplant.

=0.98 x 10800

= 10584     

6.7. Lung transplants from donors have risks. One risk is organ rejection.

Scientists are researching how to solve the problem of organ rejection and hope to use stem cells to create healthy lungs.

The healthy lungs can then be transplanted into CF patients without the risk of organ rejection.

Describe how scientists may use stem cells to create healthy lungs that are NOT rejected by the CF patient.

Ans: * Take stem cells from the patient.

* Remove CF gene.

* Create embryo using these stem cells.

* Remove stem cells and allow them to divide. 

 

             AQA GCSE Biology-1H  2018