This document contains EVERYTHING you need to know in year 1 Edexcel (A) Biology (Salters-Nuffield) for topic 2 - Genes and Health.
I have included the most important information from the book, MARK SCHEMES and revision sheets. I wrote these notes after solving all past papers and all available b...
- Seen in individuals homozygous for the recessive allele
- Faulty gene codes for the production of faulty protein – CFTR protein
- CFTR is a channel protein
- Located in the cell surface membrane of the mucus producing cells (goblet cells)
- Responsible for the movement of chloride ions across the apical cell membrane
People with CF:
- The CFTR is faulty/absent – its tertiary structure is different
- Chloride ions cannot be secreted across the cell membrane (apical membrane)
- This means that chloride ions cannot pass through the CFTR protein to enter the mucus cell,
so fewer ions will leave the cell
- Sodium channels are not blocked by the CFTR protein – always open
- Sodium ions are able to pass through the Na channels from the mucus to the cell
- More sodium ions in the cell draw chloride ions and water out of the mucus by osmosis
- More chloride ions in the cell
- Less water in the mucus making the mucus more sticky/thicker
Respiratory signs and symptoms:
- Sticky mucus blocks the airways/bronchioles
- Celia find it difficult to move the mucus out of the lungs reducing the flow of oxygen to the
alveoli, so less oxygen reaches the alveoli
- This lowers the surface area for gas exchange to take place making it less efficient
- Because Celia are unable to move particles out of the lungs, trapped bacteria may result in
more respiratory/lung infections. Other symptoms include:
- Shortness of breath, because the gas exchange system cannot deliver enough oxygen to
their muscle cells. Oxygen is needed for aerobic respiration that release energy in the form of
ATP in order for muscles to contract during exercise leading to exercise intolerance
Digestive system:
- Pancreatic cells produce digestive enzymes
- Mucus blocks the pancreatic duct - there is a lower concentration of digestive enzymes in the
small intestine
- This reduces the rate of digestion – not all nutrients are absorbed – energy is lost
- Resulting in malnutrition – lack of nutrients prevents normal growth and weight gain
- Pancreatic enzymes produce the hormone insulin – regulates blood sugar
- Mucus blocks the pancreatic duct – enzymes trapped in the pancreas can damage insulin
producing cells – fewer insulin produced – diabetes
- Can also block bile ducts in the liver – bile cannot emulsify and digest fats
, Reproductive system:
- The tubes that carry sperm are blocked by mucus and do not develop properly – infertility
- The cervix in women is blocked by mucus preventing sperm from fetilising the ovum –
infertility
Mucus traps bacteria and
Suggest how the CFTR protein is broken down provides conditions for
- Hydrolysis of the peptide bonds bacteria to live – macrophages
- Hydrolytic enzyme e.g. protease cannot destroy bacteria –
more likely to suffer from lung
infections if you have CF
2.7 PRENETAL TESTING
1. Amniocentesis
ü Involves inserting a thin needle into the amniotic fluid to collect fetal cells fallen off
the placenta / fetus
ü The cell samples of the placental tissue are then checked – DNA is extracted out of
the cell and tested for the presence of the faulty gene
ü This is to identify the mutated gene/allele à identifies genetic disorders
ü Usually carried out at 14-20 weeks
ü 1% risk of miscarriage
2. CVS ( Chronic villus sampling )
ü Fetal DNA from placental tissue is removed, either through the wall of the abdomen
or the vagina
ü And tested to identify mutated gene/allele à identifies genetic disorders
ü Carried out at 8-14 weeks
ü Higher risk of miscarriage (1-2%)
3. Non-invasive prenatal diagnosis
ü Involves analysis of fetal DNA fragments from blood samples from the mother
ü Fetal DNA becomes detectable in the mother at 4-5 weeks of pregnancy – however
levels are too low
ü Samples likely to be collected at 7-9 weeks
ü This is to identify chromosomal disorders
ü No risk of miscarriage
4. Pre-implantation genetic diagnosis (PGD)
ü Offered to pregnant women with family history of given condition
ü Combined with IVF to test embryo at 9 cell stage – DNA of the cell is analyzed
ü Tested for mutated gene/allele à identifies genetic disorder
ü Ensures that the embryo does not have any genetic disorder before being placed in
the woman’s uterus
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