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Is the poison expiring or is it more poisonous?
Image source: Pixabay
Anything that reaches a certain dose can become "poison," including water. Only typical poisons that can poison the human body with a small amount of use are discussed here.
There are many kinds of highly toxic substances - natural and artificial; organic and inorganic. For many natural poisons, such as snake venom, botulinum toxin, the main protein or polypeptide that is toxic, if not properly stored, it is easy to decompose and deteriorate, losing its original role, which means that the toxicity becomes weaker.
Pesticides used to control pests and diseases are sprayed on plants and usually decompose over time so that they do not remain on food. However, some pesticides need to be decomposed in contact with water to release more toxic volatile gases after application, which plays a role in insecticidal. This means that they may be more toxic when they are first decomposed, and it takes longer to digest the toxicity.
There are also some poisons with relatively stable chemical properties, such as arsenic trioxide (commonly known as arsenic cream, crane top red) is not easy to deteriorate in the air, but in the acidic environment will be slowly oxidized, alkaline solution will form arsenite. Regardless of which form it takes, most arsenic compounds are toxic.
Although poisons are notorious, they are also a sharp sword when used in the right place, such as pest control, rat infestation, and even become a cure. In turn, medicines that were originally used to treat diseases can become poisons if not taken properly. Although toxic agents are marked with shelf life, they are only conservative estimates of the time, and it is not excluded that they have not deteriorated after expiration, or are still toxic after deterioration.
In short, the toxicity of toxic agents is possible to become weaker and stronger over time, and this is not the "blind box" that we should gamble with our lives.
Sulfur dioxide is toxic, why can it be used to process food?
As mentioned above, it is pointless to talk about toxicity apart from dose. Sulfur dioxide with a pungent odor is classified as a toxic substance, but trace amounts of sulfur dioxide can be metabolized by the human body, and if the dosage is well grasped, it can also be used to preserve freshness and bleach without harming the human body.
Sulfur dioxide is an additive that is allowed and commonly used at home and abroad, from all kinds of food, beverages, to daily necessities such as paper towels, sulfur dioxide is everywhere. It is usually added in the form of sulfites in food as preservatives and antioxidants, or sulfur dioxide is produced by sulfur fumigation for bleaching. Foods using sulfur dioxide or sulfites must be indicated in the ingredient list, and there are strict requirements for dosage.
The tetravalent sulfur in these sulfides is reducible and bleached. Its reducing capacity inhibits the activity of bacteria, mold or oxidase contained in the food itself, so that the food is not oxidized and deteriorated or browned. Fruits and vegetables, fruit and vegetable juices, preserved fruits, wine and other foods are often used in this way to extend the shelf life. The ability to bleach is reflected in its ability to combine with colored substances to make food white. White sugar, rice flour, white fungus, and paper towels will appear whiter after sulfur dioxide treatment.
However, in order to make the original not-fresh food appear particularly bright, some unscrupulous merchants use sulfur dioxide excessively, which will lead to excessive residues, exceeding the metabolic capacity of the human body and endangering health.
Why don't proteases break down each other?
Proteases are a large class of enzymes that specialize in breaking down proteins, such as pepsin and trypsin, which help us digest food. However, these enzymes are also proteins themselves, so why didn't they break down each other?
Proteins are composed of various amino acids, each amino acid is connected into a polypeptide chain by forming a peptide bond, and then one or more polypeptide chains are coiled and folded into proteins. Only by maintaining a certain spatial structure can proteins perform specific functions, and the same is true for enzymes.
The structure of proteases | Source: Wikimedia Commons
Proteases, as "principled" biological catalysts, do not catch any protein and unload eight pieces, they will only pick the specific peptide bond of the protein under specific conditions (suitable pH, temperature, etc.). And they each have their own cutting style, some specifically cut from the inside of the peptide chain, and some like to cut from both ends of the peptide chain.
Take pepsins, for example, which exist in the form of proenzymes when they are not working, and only after being activated by gastric acid will they vigorously cut proteins. Pepsin cleavage sites are broad, exhibit different specificities at different pH values, and generally prefer peptide bonds on hydrophobic amino acids. Many proteins have these loci, pepsin itself, but because proteins have a spatial structure, if these loci are hidden inside, proteases are not enough, which is why pepsin is not easily broken down by the same kind. And the proteins we eat can't withstand stomach acid, and after denaturation, the weakness is exposed, and it is dismantled by pepsin.
Similarly, if a protease exposes its weaknesses due to environmental changes, it may also be broken down by its own kind or other proteases.
Is the zebra black on a white background or a white stripe on a black background?
Zebras wear trendy black and white striped shirts, but the black and white stripes are not so evenly distributed. From the belly, it seems that white prevails, and it feels like black lines on a white background.
"Horses cannot be disguised", take off the fur coat of the zebra, it is actually a "black horse", not a white horse. The zebra's skin is black, which is "dyed" by melanocytes in the skin, which are also present in the hair follicles and determine the color of the animal's hair. Melanin produced by melanocytes makes our skin and hair appear different colors, more dark and less light.
For zebras, skin melanocytes are more "ink" by default, and those "lack of ink" white hair is the result of melanocytes in the hair follicle not producing melanin, so it is more appropriate to say that zebras are "white on a black background" than "black on a white background". Of course, the most innocuous statement should be black and white on a black background.
Unlabeled image source network.
References are stored in graphite:
https://shimowendang.com/docs/pKw6HTvdgyJcVrxt
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