I studied the Edexcel syllabus for my Chemistry A-Level, and many of the concepts I learned about at school have subsequently reappeared at university. Here’s a guide to some of the A-Level Chemistry themes which have cropped up again while I’ve been studying Medicine.
A huge theme in pharmacology so far has been the weak acid and the weak base. At A-Level, I learned about dissociation and the pKa value of a given weak acid or base. Many drugs are weak acids or weak bases.
For example – let’s consider aspirin, which is a good example of a weak acid. At Medical School, we have learnt that a drug will be in its active form when it is ionised, i.e. aspirin will help to relieve pain when it is ionised. However, a drug will only be able to cross a membrane when it is in its unionised form. So after an oral aspirin has been taken, it will only be able to move from the GIT into the blood and to the target tissue when it is not ionised.
Therefore, we can consider if the aspirin is found in an acidic environment, whether a greater or lesser proportion will be found in its unionised form, and how much aspirin will move across the membrane and then become ionised to become active and relieve pain. My understanding of pKa and pH, plus the ionisation of weak acids and bases, from A-Level Chemistry has really helped me to understand this pharmacological principle.
During A-Level Chemistry, I also learned about a weak acid or base’s ability to act as a buffer – and how at equilibrium, the system may shift to the left or the right to counteract a given change. The blood depends on the bicarbonate buffer system to maintain the pH ~ 7.4. If pH<7.35, the blood has become acidic, and if pH>7.45, the blood has become alkalotic.
(H2O + CO2) → H2CO3 → HCO3- + H+
H2CO3 will act as a weak acid whereas HCO3- will act as the conjugate base.
If someone experiences a respiratory acidosis, the lungs will not be able to remove all the CO2 from the blood, which will dissolve to form carbonic acid (H2CO3) and decrease pH. Therefore, the buffer system will shift to the right in order to produce more conjugate base to decrease pH.
At A-Level, I learned about chirality and the importance of the optical isomer. This has particular significance in certain drugs such as Thalidomide, which was part of the A-Level Chemistry syllabus. It was important to note that one optical isomer relieved morning sickness and the other isomer gave rise to disabling congenital defects in infants.
Optical isomerism is an important concept to understand in pharmacology. When learning about the GIT at Med School, we have studied a drug called omeprazole which is a proton pump inhibitor. Omeprazole is a medication used in the treatment of gastroesophageal reflux disease and it decreases the amount of acid which is secreted by the stomach to reduce the effects of heartburn. Unlike thalidomide, omeprazole is a racemate and both forms of the isomer ultimately lead to the inhibition of the same enzyme (H+,K+-ATPase) so both reduce gastric acid secretion.
When we studied glycolysis and the Krebs cycle involved in metabolism at Med School, my A-Level Chemistry served me very well! Firstly, it was important to be able to recognise different types of sugars and their chemical groups, e.g. aldose has the aldehyde functional group, whereas a ketose has the ketone functional group.
One of the first steps of glycolysis was the isomerisation step, in which an enzyme moved a carbonyl group from carbon 1 to carbon 2 to form a fructose derivate from a glucose derivative – which the next enzyme can now act upon. Isomerisation is a very important concept throughout respiration, and a knowledge of different types of structural isomers in organic chemistry really helped me to grasp these concepts.
Inhibition of certain enzymes is a concept which I was also introduced to during A-Level Chemistry. Downstream products from previous steps of glycolysis can allosterically inhibit certain enzymes which regulate glycolysis. The self-regulating nature of the process fascinated me, and it was supported by my understanding of A-Level Chemistry. We can also consider the rate of reaction and kinetics, as well as the effect of temperature/pH and enzyme on the rate of a given reaction.
Blood clotting is a highly complex process, controlled by many co-factors, enzymes and precursor molecules in a clotting cascade. Reduced vitamin K acts as a cofactor to an enzyme which will activate certain factors in the terminal stages of the clotting cascade.
During A-Level Chemistry, I learned that oxidation is a loss of electrons or a gain of hydrogen ions, and reduction is a gain of electrons or a loss of hydrogen ions. Reduced vitamin K will reduce a certain enzyme which will activate certain clotting factors. Once oxidised, vitamin K will be reduced via the enzyme vitamin K reductase. This knowledge of clotting is determined by an understanding of redox reactions, which I studied at A-Level.
Taking this one step further, warfarin is an anticoagulant medication to reduce the formation of blood clots and their associated risks. Warfarin is an inhibitor of vitamin K reductase. Using A-Level Chemistry knowledge, this will mean that vitamin K remains oxidised and cannot reduce the enzyme necessary to activate clotting factors. Therefore, there will be reduced blood clotting.
Check out this guide to surviving your first year of Med School to discover what else you can expect to face as a new Med student – including dissection, patient interaction, and your first exams.
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