The ABCs of Chemistry: Part 6
By Lydia from SLN More Blogs by This AuthorFrom the Science Bits in a World of Bytes Blog Series
I say that I’m not that interested in biochemistry, and in some ways that’s true. I’ve yet to do any type of blot or assay, although I worked with a calorimeter during undergraduate research. In my consideration, environmental geochemistry was one of the best classes I took. There still, however, lies an interest in biomolecules. I’ve mentioned how aspirin works, why eating too much pepper causes pain, and the chemistry of vision. The contradiction continues below.
S is for Steroids
With Lance Armstrong’s doping recently in the news, people are interested in steroids. Steroids are joined under their characteristic four-ring core, seen above in the image of cortisone. Different steroids attach different functional groups to this core. There are five different kinds of steroids. Androgens, like testosterone and estrogen, influence the development of sexual function and characteristics. Progestins, like progesterone control the menstrual cycle and pregnancy. Glucocorticoids, such as cortisol, control the metabolism of carbohydrates, proteins, and fats. Minerlaocorticoids do the same for salts in the tissues, and bile acids, like cholic acid, assist in absorption of lipids in the intestine.
The most famous steroid is cholesterol. It is a building block for all other animal steroids. It part of the plaque that can coat arteries and fat-protein complexes in the blood. The –OH group on one end allows it to park in a cell’s plasma membrane. This feature is useful in preserving the integrity of the membrane. As the membrane is heated, the lipid molecules twist and become more disordered, making the membrane thinner. The cholesterol molecule slides between adjacent fat molecules, preventing them from sliding and tangling with each other .
The steroids used in doping are designed to induce the effects of testosterone, which is mostly deactivated when taken by mouth. For example, testosterone has different groups added to it before it is injected. The body hacks off these groups, leaving testosterone free to bind to the androgen receptor. The steroids induce anabolism, or cell growth, by increasing protein synthesis, elevated production of red blood cells, and hunger, to name a few. These steroids also have virilizing effects on women, such as the deepening of the voice. Curiously, the anabolic steroids have a feminizing effect on men.
T is for Trinitrotoluene
The name is a mouthful that requires a semester of organic chemistry to picture. It’s better known by its shortened form, TNT, an explosive used to move lots of stuff fast. It is made by adding three nitro (-NO2) groups to methylbenzene (toluene). The addition is done in three carefully-controlled steps to make sure the nitro groups are in the correct spots and to prevent an explosion.
Although the synthesis requires special care, the molecule itself is not that sensitive to friction and shock, like dropping, so it is a useful explosive. TNT is so potent that all other explosives have their power measured relative to it. It can be used in wet conditions, and it melts far below temperatures that would detonate it, so it can be molded. It is often combined with oxygen-containing explosives to increase its energy per kilogram.
The molecule was originally used as a yellow dye. No one thought to use it for explosions because it was difficult to detonate. However, once its utility was recognized, use took off, so to speak, like a rocket. Widespread use led to the health consequences. WWI munitions workers found that it turned their skin yellow. Chronic exposure at medium to high dosage (0.5 mg/kg/day – 200.0 mg/kg/day) affects the liver, raising bilirubin levels and causing cirrhosis. It also raises triglyceride and cholesterol levels. Six of twelve wartime TNT workers developed cataracts. This substance is useful but must be handled with care.
U is for Urushiol
Unlike many other compounds, urushiol gets its name from Japanese. It might sound exotic, but it’s a down-home bother. It’s the active component in the oil of poison ivy and poison oak. The structure varies slightly from plant to plant. The core is a catechol molecule, benzene with two –OH groups on adjacent carbons. A long carbon chain hangs off a carbon next to an –OH group. The length can vary. For instance, poison ivy and poison sumac have a chain 15 carbons long, while poison oak tends to have a seventeen-carbon chain. The picture shows some possible side chains for poison ivy and poison sumac. The wavy line shows the end of the chain that attaches to the catechol.
The degree of unsaturation of the chain, that is, the amount of double bonds, affects the severity of the reaction to the oil. The top, totally saturated chain, produces a reaction in fewer than half the people exposed to it. The bottom chain, however, produces a reaction in 90 percent of those exposed to it. The chain length also has an effect; longer chains produce stronger reactions.
Urushiol has a particularly bothersome method of action that requires days or weeks to pass before the full extent of symptoms is displayed. This is bad news, because urushiol can be washed off with cold water and soap within a few minutes of exposure. The urushiol passes through the skin and attaches to the membrane of a type of cell called Langerhan cells. These cells head to a lymph node, where helper T- cells, a type of white blood cell, might attach to it. The helper T-cells send out proteins called lymphokines, which attract other white blood cells, including killer T-cells and macrophages. These white blood cells release a horde of chemicals that destroy everything in the vicinity, including skin cells infected with urushiol. This is what causes the blistering and oozing of skin.
A select few individuals are immune to the action of urushiol. This has been traced to the T-cells. A person who is immune might have fewer helper T-cells overall or not have one with the receptor site for urushiol. A protein called IgG can block the receptor site for urushiol. Finally, suppressor T-cells can live up to their name and hold back the expression of other T-cells.
V is for Vanillin
Vanillin is the primary flavor constituent of vanilla beans (about two percent by weight). It is found at low amounts in many other comestibles, like raspberries, olive oil, coffee, and maple syrup. Vanillin is produced by a species of orchid native to Mexico. The green pods contain vanillin attached to a glucose molecule, so the molecule does not have its vanilla flavor yet. Several months of curing bring out the vanilla flavor. The pods are first blanched (boiled briefly) to stop whatever is happening in the cells. Then, the pods are laid out in the sun during the day and brought in and wrapped up at night to sweat. This turns the pods dark brown. The pods are dried for several more months before being considered finished.
See? Don’t you feel better about buying synthetic vanilla flavoring?
The body metabolizes vanillin to several products. One study found that major metabolites included vanillic acid, where an –OH was added to the aldehyde (-CHO group), vanillyl alcohol, where the aldehyde is reduced to an alcohol (-OH), and vanilloylglycine, where the amino acid glycine was added to the molecule. This was determined to happen by first joining the alcohol group to a sulfate or glucuronic acid. Then, the aldehyde was oxidized to a carboxylic acid (-COOH).
Something good for you, something bad for you. Chemistry is full of that. I have a proclivity toward vanillin; I like almost any candle that smells like cookies or cupcakes. I also feel like I have a taste bud for cholesterol sometimes. Pass the cheese and ice cream, please. That, however, is the only steroid I have deliberately ingested. They might be good or bad, but they do have something in common. Every one used rings, and all but one had benzene. Chemistry really makes things go (‘)round!
Armstrong, WP. "Poison Oak: More Than Just Scratching the Surface." Wayne's Word. N.p., 16 Jan 2011. Web. 29 Mar 2013.
Garrett, Reginald, and Charles Grisham. Biochemistry. 2nd ed. Boston: Brooks/Cole, 1999. 254-256. Print.
Ford, Theresa. "Urushiol Resin." Poison Ivy Tutorial. N.p., 22 Jan 2010. Web. 29 Mar 2013.
Sammons, HG, and RT Williams. "Studies in detoxication: The Metabolism of Vanillin and Vanillic Acid in the Rabbit. The Identification of Glucurovanillin and the Structure of Glucurovanillic Acid." Biochemical Journal. (1941): 1175-1189. Web. 29 Mar. 2013.
Strand, LP, and RR Scheline. "The Metabolism of Vanillin and Isovanillin in the Rat." Xenobiotica. 5.1 (1975): 49-63. Web. 29 Mar. 2013.
Also thanks to PubChem Sketcher Version 2.4 and Wikipedia