On 24th of June, Amber Ahark (Y11), who has written an article about poisonous frogs during the COVID-19 lockdown, did a virtual Café Sci talk about her research. She told us how poison frogs are able to hold a neurotoxin within their skin, called batrachotoxin (BTX), which is capable of killing 20,000 mice or the equivalent of 10 grown men. A rare breed of frog called Phyllobates terribilis which originates from Colombia and are bright yellow in colour. Their sizes vary from 1.5 to 6cm. These poisonous frogs secrete the venom from their skin, as the BTX toxin is stored in glands beneath their skin; they absorb the toxins and chemicals from prey such as mice and ants. Once the toxin is injected into an animal, then the toxin disrupts the nervous system by tearing open sodium channels and interferes with the body’s ability to transmit electrical signals. This then leads to hypertension, fibrillation, heart failure or in more severe cases, a seizure. The toxin BTX belongs to the alkaloid group[1] and this was isolated from the bodies of the frogs in Colombia to shoot poison at enemies using blow darts. It is argued that BTX could be used in the future to formulate pain killers, as it has been synthesized and reproduced in laboratories using cis-decalone. The structure of BTX includes a steroid skeleton and an oxazapane ring and the activity of BTX depends on temperature, reaching its maximum at 37 degrees Celsius. However, poisonous frogs are not the only creatures to contain traces of BTX. It was found that Choresine beetles also had high concentrations of the neurotoxin and this leads to speculation that these beetles could be a staple part of the frogs’ diets, as they sequester the toxin from their prey. Essentially, BTX poisons the body by interfering with nerve signals. Within our cells, we have a high concentration of sodium ions outside our cells while the potassium ions are more concentrated within our cells. The movement of these ions are controlled by channels (sodium and potassium channels), and the sodium channels are closed. However, when BTX enters the body, it rapidly opens these sodium channels and it binds to the threshold voltage. BTX inhibits nerve impulses, by binding to the gates of the sodium channels and it becomes irreversible- so the sodium channels cannot be closed. Ultimately, this suggests that the survival rate against BTX is incredibly slim. However, how do poisonous frogs manage to store the neurotoxin within their bodies?
A 2014 study from John Carroll University discovered that the mother frogs give the tadpoles poison, which they absorb to become poisonous themselves. As tadpoles, their mother feeds them her own unfertilised eggs, which contain BTX. Although, these poisonous dart frogs were never poisonous, they evolved to become poisonous and store toxins because of a mutation. This was a very small mutation, where three of the 2,500 amino acids in a receptor changed. This mutation prevented BTX from damaging their own receptors and destroying their nervous system, making them resistant. The mutation that makes the frogs resistance to the toxin occurs in the parts of the receptor that are close to but don't touch the toxin (epibatidine). The amino acids are never in contact with the neurotoxin, yet they can still change the receptor. The receptor's key function was maintained by additional amino acid replacements allowing them to resist their own toxins, while still maintaining the normal function of their target neurotransmitters. Furthermore, some poison frogs managed to retune a neurotransmitter receptor so that it also became insensitive to another toxin, called epibatidine. Overall, despite these poisonous frogs being lethal and capable of killing humans due to the neurotoxin BTZ, they don’t produce it themselves, but sequester the toxin from feeding off their mother’s unfertilised embryos and their prey. Additionally, due to a mutation, their receptors are resistant to the toxin because of a change in their amino acid sequence within their receptors.
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Professor Harrison began by explaining the origins of particle physics and how ancient Greek philosophers questioned what happens when you keep slicing something up – if you eventually reach an elementary level at which further cutting of it would fundamentally change the substance or whether it just gets infinitely smaller. Leucippus and Democritus proposed that the substance would not get infinitely smaller but that you would eventually reach an ‘atom’, meaning ‘indivisible’. 2000 years on we now know much more about what happens when we cut an object into continually smaller objects. Bulk matter is anything greater than 10-9m, atoms and molecules are between 10-8m and 10-10m. Within an atom’s inner structure there is a nucleus of size 10-14m which contains nucleons (protons and neutrons) that are 10-15m containing quarks which are 10-20. Quarks are a type of elementary particle – a particle which has no known structure but makes up larger things. There are different types of elementary particles: quarks, leptons, gauge bosons and scalar bosons. Within these categories there are different types of elementary particles, for example up, down, charm, strange, top and bottom are all types of quark. Professor Harrison then went on to explain how there are 4 guiding principles of Particle Physics – these are: Simplicity, Composition, Unification and Symmetry. With Simplicity Ockham’s Razor is used and this is a philosophical principle that if there are multiple explanations for something then the simplest one is best. Unification is used when trying to explain different physical phenomena using a single idea or law of nature, for example with Coulomb’s Law of electric field around a charge, Amperes Law of Magnetism and Faraday’s Law of Induction, Maxwell was able to show that these were all linked by ‘fixing’ one – allowing him to predict electromagnetic waves. With Symmetry, Noether’s Theorem (1915) is used, ‘Every symmetry of the laws of Nature implies an associated Conservation law’. Next Professor Harrison spoke about the tools of Particle Physics, both theoretical – Quantum Mechanics, Einstein’s Theory of Special Relativity – and things like the Large Hadron Collider and ATLAS. He finished by mentioning some of the unanswered questions such as, ‘Is the discovered Higgs boson the only Higgs boson?’, ‘Why is the Higgs boson mass stable?’, ‘Is the dark matter of the Universe really a new undiscovered particle?’, ‘Is there a way to unify the strong interaction with the weak and electromagnetic?’ and ‘Why do the masses of the elementary particles take the values they do?’.
Overall, this was a really interesting talk on a fascinating area of Physics that clearly has much more research yet to be carried out. |
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June 2020
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