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4 - Molecular biology in medicine

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Rational Drug DesignMalaria

Text of 4 - Molecular biology in medicine

  • 1. Chapter 4: Molecular biology in medicine.

2. Background 3. The beginning The first link between genetic inheritance and a human condition was made in 1902 when alkaptonuria was identified as an inherited disorder. (51 years prior to Watson & Crick discovering DNA) Alkaptonuria is a condition in which urine turns black on exposure to air. Sir Archibald E. Garrod (18571936) related this and similar diseases to a lack of particular enzymes in the body. 4. CausesGenetic defects can be due to problems withan entire chromosome, multiple genes, oreven a single gene (section of achromosome).The human Globin gene is 626 base pairslong. If a single base substitution mutationoccurs in a particular place, the person willdevelop Sickle Cell Anaemia.Eg: small section of geneACT CCT GAG GAG AAG (unaffected person)ACT CCT GTG GAG AAG (sickle-cell individual) 5. Inherited diseases 6. The following conditions can be tested by conductiong a simple heel-prick test on a baby 2-3 days after birth,1. Phenylketonuria (PKU) is a disorder characterized by an inability toproduce the enzyme phenylalanine hydroxylase, resulting in apotentially fatal or damaging build up of the amino acidphenalalanine, and occurs in one in every 10000 babies.1. Hypothyroidism is a disorder caused by a small or improperlyfunctioning thyroid gland, or even its complete absence, and occurs inone in every 3500 babies.2. Galactosaemia is an inherited disorder and occurs in one in every40,000 babies. Lactose is digested into galactose and glucose. A babywith galactosaemia lacks the enzyme that metabolises galactose andwill die if untreated because of the build-up of galactose in the blood.3. Cystic fibrosis (CF) is an inherited disorder and occurs in one in every2500 babies. A person with CF produces abnormal secretions thathave a serious adverse effect on the function of lungs and digestion.Recent advances in treatment have greatly improved the prognosis forthese babies so early diagnosis and treatment are important 7. Early detection 8. PKU a case study The aforementioned conditions are tested for at birth as earlydetection is essential in successful treatment. Individuals born with PKU cant produce phenylalanine hydroxylase(an enzyme). Many products contain the amino acid phenylalanine, which cant bebroken down, the build-up starts to destroy brain tissue, therebyhaving a detrimental effect on development. Initial detection technique was the wet nappy test using ferricchloride but this often occurred too late 9. PKU a case study An alternative technique was the Guthrieplate. Blood was collected via the heel pricktest. Foetal blood was tested for high levels ofphenalalanine. Using bacteria that wouldonly grow under certain concentrations Blood is still collected via a heel prick testbut can be tested far more efficiently viamass spectrometry (a biochemical analysisof the make-up of the babies blood) 10. Gene Therapy 11. Gene therapy Many genetic diseases are caused by a single gene. Eg: PKU this single gene defect, could be treated by consuming a special diet. This approach is not possible with many conditions. Why not try to insert a normal functional gene into cellsthat contain a defect? Such a procedure is called gene therapy and is a medical procedurethat modifies the genetic material of living cells of an individual so that agenetic defect is corrected. 12. Gene therapy 13. Transferring a piece of DNA into a cell The functional piece of DNA inserted into a cell is specially prepared and is called a cloned gene. How does the cloned gene, get into a patients cells? This action is most successful when a vector is used to carry the gene into a cell. The most commonly used vectors for gene therapy are modified viruses. (Retroviruses and adenoviruses are the main types used.) 14. Gene therapy using aretrovirus vector: Some viruses have DNA, some have RNA,Retroviruses have RNA that codes for DNAonce it enters a cell 1 remove harmful RNA but leave bits thatcode for infection and transformation to DNA 2 insert RNA version of normal gene in tovirus 3 introduce virus to cells ex-vivo and allowcells to replicate 4 inject infected cells in to patient 15. Gene therapy using an adenovirus Adenoviruses contain DNA, in to which a normal copy of agene can be integrated When the adenovirus enters the host cell, its DNA enters thenucleus and starts coding for the required proteins. Adenovirus DNA does not integrate with host DNA, so whenmitosis occurs, it does not replicate. 16. Prenatal testing 17. Success of gene therapy Many successful experiments have been conducted with animals such as mice Still very experimental in humans and can pose risks to patients safety. Non-viral gene therapy would be very difficult as this is one of the few ways of bypassing our immune system 18. Screening during PregnancyUltrasound is commonly used to view theuterus and fetus during pregnancy. Scans are often performed at 18 to 20 weeks into a pregnancy. Ultrasound maybe performed earlier if there are signs or indications that the fetus is not growing normally. Ultrasound is also used to diagnose: multiple pregnancies (twins, triplets) gross fetal abnormalities such as trisomy (e.g. Down, Klinefelter, and Turner syndromes) 19. Other types of pre-natal testing CSV (Chorionic Villus Sampling) Performed at 6-8 weeks Material gathered can be used for both metabolic and genetic testing AmniocentesisAmniotic fluid contains both skin cellsand urineThin tube extracts fetal tissue Material gathered can be used for both metabolic and genetic testing Miscarriages are often not random occurrences but actually the result of the foetus dying doue to a genetic abnormalityAmniotic fluid 20. Genetic Testing 21. Electrophoresis DNA collected during screening procedures can be cut in specificlocations using REs (restriction enzymes). The DNA can be run through an agarose gel. A current is put throughthe gel. DNA is negatively charged and will be drawn towards the positiveterminal. Smaller fragments will move faster while larger fragment will take moretime to move through the gel Every person has 2 copies of every gene and depending on theabnormality, these can be observed on the gel 22. In this case the disease form of the gene is smaller than the normalversion The gel shows that both parents were carriers for the condition and thattheir first child received each parents diseased gene and therefordeveloped the condition. Fortunately their unborn child received both normal versions of the gene 23. OTHER CONDITIONSThe age of onset of many geneticconditions can vary: 24. Genetic disease vs predispositionDISEASE If you have two affected copies the Huntingtons gene you areguaranteed to get the disease. Onset is usually around the age of 40 and manifests in fairly rapidbrain degeneration. There is no currently available treatmentPREDISPOSITION If you have affected copies of the BRCA1 or BRCA 2 genes for breastcancer, there is no guarantee that you will get the disease. You have a much higher chance of it developing it, but the rightenvironmental conditions are required to trigger its onset 25. Genetics and DiseaseDown syndrome is oftencharacterized byimpairment of cognitiveability and physicalgrowth, as well as somevery recognizable facial21featuresIt is caused by an individualbeing born with a 3rd copyof chromosome 21, due to aseparation error duringmeiosis. Photo: Art TodayOccurrence is estimated atapproximately 1:750 births. 26. Who should be screened Anyone with a history of genetic disease Two unaffected individuals who have had an affected child areboth carriers of a recessive disease. Their chances of having another affected child are 1 in 4 An affected individual with a dominant disease has one orboth of their alleles carrying the disease They have a 1 in 1 or at best a 1 in 2 chance of having anaffected child 27. Rational Drug Design 28. Rational drug design When our immune system fights off the flu it develops a memory of it, the next time we encounter the same strain we may not even develop symptoms before it is fought off. The problem is that new strains are constantly appearing, so the process must be repeated time and time again. Two surface proteins on influenza virus: Haemagglutinin is active in gaining entry to a cell. Neuraminidase allows the exit of new virus particles from acell, freeing them to infect other cells. 29. Rational drug design Neuraminidase is an enzyme that varies in structure from strain to strain. Examination of strains of the virus from past years demonstrated that although mostof the molecule changed dramatically, one small part remained constant. Fortunately, this non-variable part is the active site of theenzyme. 30. Using the active site If a drug was to be designed to inhibitthe active site of neuraminidase, the molecular structure of the sitehad to be worked out. This was done by computer modelling sothat the active sites exact shape and theComputer representation of thespatial arrangements of the atomsanti-flu drug in the activesurrounding it became known.site of neuraminidase. 31. Designing the drug Once the detailed structure of the active site was known a molecule could be designed to fit and bind to the active site,Photo: CDC Then an anti-flu drug was created! This technique, in which the active site of a molecule is determined and a second molecule (the drug) is constructed to fit into that active site to inhibit the activity of the first molecule, is called rational drug design. 32. How does it work? 33. Developing Vaccines 34. Types of VaccineThere are two basic types of vaccine:subunit vaccines and whole-agent vaccines.RecombinantvaccinesSubunit VaccineContains some part or Toxoids product of micro-organisms that canConjugated produce an immune responsevaccines Acellular vaccinesAttenuated Whole-Agent(weakened) Vaccine Contains w

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