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Asked by #nerdyweirdo to Chris, Josh, Rebecca, Rob, Susan on 22 Jun 2015.
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Rebecca Dewey answered on 22 Jun 2015:
Every poison works slightly differently. The general theme is that poisons get into your body and change some process that you cannot live without.
For example carbon monoxide: when you breathe carbon monoxide in, it enters your lungs and attaches itself onto red blood cells at the place where the oxygen normally attaches. Once a carbon monoxide molecule has attached to a red blood cell, it is very hard to get the carbon monoxide, so that blood cell will remain useless until the body decides it is old enough to be removed and replaced.
Another example: lead. Lead replaces calcium in several of the places where your body needs calcium to function, e.g. in the bones or in the brain. In the brain, calcium ions are used a lot to help send messages from braincell to braincell. Lead this causes the brain to develop and function incorrectly, leading to problems in brain function.
Paracetamol is a pain killer that can be bought from most shops. But it is poisonous to the liver in large doses. Usually, the liver processes chemicals like paracetamol and removes them from the blood stream. But if you have too much of it in your body, the liver can’t remove it like usual, and this kills liver cells. Once the liver has started to fail in this way, it is very difficult to get it to return to normal health again.
So basically, there are lots of different ways that poisons work to change or mess up something that your body needs to survive.
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Susan Cartwright answered on 22 Jun 2015:
There are many different ways in which poisons work (note: a poison is something that will harm you if you ingest it, either by eating or breathing; something that is only toxic when injected into the bloodstream is a venom). To generalise wildly, what they do is sabotage some process that is required to keep you functioning.
A very clear example is carbon monoxide (CO). CO binds to the same site in haemoglobin (the oxygen-carrying molecule in red blood cells) that oxygen does – but then it doesn’t let go. So, if you breathe in carbon monoxide, you will slowly suffocate, as more and more of your haemoglobin is bound to CO instead of transporting oxygen.
Arsenic, that staple of old detective stories, deactivates a crucial enzyme and prevents the body from metabolising thiamine (alias vitamin B1). Its symptoms resemble B vitamin deficiency, which is why it was hard to diagnose – and thus a good choice for murderers – before the advent of chemical tests.
Strychnine, another classic poison, disrupts the activity of the neutrotransmitter glycine, causing over-activation of muscle contraction, muscular spasms, and death by respiratory failure because the muscles that control your breathing don’t work properly.
The heavy metal thallium is taken up by the body in mistake for potassium, because the Tl+ ion has some similarities to K+. However, the chemistry of thallium differs considerably from potassium (potassium is an alkali metal with valence 1, thallium is a group 3 metal with valence 3), so taking up thallium instead of potassium does horrible things to cell chemistry. Thallium compounds can be tasteless and odourless, which makes them a great choice for the discerning murderer.
Ricin, a poisonous substance found in the seeds of the castor oil plant, disrupts the machinery that enables cells to transcribe DNA and make proteins. This is not too serious when eaten, because the symptoms tend to be confined to the gut lining (which is anyway replaced frequently by the body) but can be nasty when inhaled or injected.
Botulinum toxin, an unbelievably poisonous substance – inhaling one millionth of a gram of the stuff will kill you – is another poison that interferes with a neurotransmitter, this time acetylcholine. Acetylcholine is used by motor neurons to control muscles, so botulinum poisoning – botulism – is characterised by paralysis, and kills by paralyising the respiratory system. Because of its ability to paralyse muscles, botulinum toxin – in absolutely minute amounts, less than a billionth of a gram – is used to treat medical conditions that involve involuntary muscle movement, and also by the cosmetic industry to reduce wrinkles by paralysing the muscles of your forehead!
These are just a few examples. There are loads more. Being poisonous is an excellent way of arranging not to be eaten, so plants and animals have been happily evolving new poisons since the dawn of life. (This is one reason why “all natural” doesn’t necessarily mean “good for you”!)
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