When we think of the deadliest diseases of the world, things like Ebola and the Black Death come to our minds. However, it turns out that cardiovascular disease (CVD) is the world’s leading cause of death in this day and age. In the 1970s, we were convinced that CVD was caused by dietary fat. Indeed, there was a public campaign to stamp out fat and replace it with carbohydrates. People didn’t realize that fat wasn’t the issue. Rather, fat has the highest calorie/mass ratio (9 calories per gram) and excess consumption of fat leads to obesity and its milieu of problems, including CVD. The food industry replaced fat with carbohydrates to meet this craze, and “fat-free” foods were instead pumped with sugar. Of course, calories are calories—and when people consumed these foods in earnest, not much changed with regards to the incidence of CVD.

So what exactly is fat? Chemically, fat is a glycerol molecule + three fatty acids. Fatty acids are long-chained aliphatic carboxylic acids that are either saturated (only single bonds) or unsaturated (one or more double/triple bonds). Quick aside: in popular culture, we hear about “omega-3 fatty acids” and “omega-6 fatty acids.” This refers to the position of the first double bond in the fatty acid, with the omega position being the last carbon in the chain (see picture below). So an omega-3 fatty acid is a fatty acid that has its first double bond on the 3rd carbon from the omega position.

Origin: Greek, glykeros (sweet) + –ol (chemical suffix for alcohols)
So named because glycerol is, in fact, sweet (and is an alcohol)

triglyceride glycerol

Origin: Greek, aleiphar (oil)
Refers to hydrocarbons that do not contain benzene rings

What about the term lipid [Gk. lipos (fat)]? In the vernacular, people equate the word “lipid” to “fat,” and its etymology certainly vindicates such an equation. But of course, we must be rigorous with our definitions. To start, fats (i.e., triglycerides) are certainly a lipid subclass. Other subclasses include waxes (fatty acid esters such as beeswax; article’s featured image) and sterols (isoprene-derived steroids such as cholesterol). One classical definition of a lipid is the following: lipids are hydrophobic (some also include amphiphilic) small molecules that can dissolve in organic solvents but not water.

Origin: Greek, hydor (water) + phobos (fear)
Fear of water, i.e., not dissolvable in water or other polar solvents

Origin: Greek, amphi – (both) + philia (love)
Love of both water and fat, i.e., dissolvable in polar and nonpolar solvents

For those who love math, recall that for a statement to be proven true, it must be true in all instances. For a statement to be proven false, one need only provide a counterexample. So my counterexample for this definition of lipid is the molecule carbon tetrachloride (CCl4). CCl4 is a small molecule, it is hydrophobic, it dissolves in organic solvents, and it doesn’t dissolve in water. Now, to patch the definition up, one can make an addendum to include “naturally-occurring.” Needless to say, CCl4 is not naturally-occurring. Is there another definition of lipid that you prefer? Let me know in the comments!


Before ending this post, I would like to touch on the significance of fat in disease. There are a number of disease states that manifest with malabsorption; one of them is coeliac disease. The diarrhea that coeliac patients experience after ingesting gluten is more accurately termed steatorrhea:

Origin: Greek, stear (fat) + rhein (to flow)
Flow of fat (through the intestines), i.e., fat in the stools

How can you identify steatorrhea? If the stool is especially foul-smelling and sticks to the sides of the porcelain shrine, you’ve got yourself a flow of fat.

Thanksgiving is upon us, and next to the fastidious references to pumpkin spice lattes and the like, the reference that we perpetuate and perhaps look forward to is that of the classic Thanksgiving postprandial somnolence.

Origin: Latin, post- (after) + prandium (meal)
After a meal, especially dinner

Origin: Latin, somnus (sleep)

Now, what is the soporific agent responsible for sending us on our merry way to the arms of Hypnos? Most people would tell you that copious amounts of tryptophan are responsible. Tryptophan is one of the 20 amino acids that are used to synthesize proteins in our bodies, and it is said to be abundant in turkey meat.

Tryptophan was first isolated in 1901 by Frederick Gowland Hopkins through the hydrolysis of casein; casein is one of the proteins that are abundant in milk. (Interesting aside: casein has an affinity for the molecule capsaicin, which is found in chili peppers. This is why dairy products neutralize the spice from peppers.) Hopkins conducted an animal study in which he removed tryptophan from the diets of mice. He found that tryptophan was necessary for the mice to grow, and concluded that tryptophan is one of the “essential” amino acids, i.e., it must be obtained through the diet. In 1912, he conducted another animal study in which he supplied mice with pure proteins, fats, carbohydrates, and minerals. He found that the mice did not grow, and postulated that there exist unidentified “accessory food factors” necessary for growth and survival. These “accessory food factors” are better known to us now as vitamins, and for this realization, Hopkins was awarded the Nobel Prize in Physiology or Medicine in 1929.

hopkins tryptophan

Now, regarding tryptophan: where does the word come from? Let’s start with some etymology:

Origin: Greek, trypsin (digestive enzyme) + phanein (to show)
Something that is shown when trypsinized

Thus, tryptophan is so named because it is “shown” (produced) when proteins are digested with the enzyme trypsin. The etymology behind trypsin is rather cool as well:

Origin: Greek, tribein (to rub)
So named because it was first obtained with rubbing the pancreas

Anyways, it turns out that tryptophan is not the agent responsible for the ol’ Thanksgiving food coma. It has been shown that chicken and beef contain similar quantities of the amino acid. Instead, it is the large amount of carbohydrates ingested through classic Thanksgiving dishes such as mashed potatoes, yams, stuffing, etc. I won’t bore you with the posited mechanisms behind this, but there are a number of online resources that could fill you in if you so choose. Let us part with another fun Thanksgiving etymology:

acholeus rev

The Banquet of Acholeus by Rubens (1577-1640)
(Heracles fought against Acholeus for the hand of Deianeira, and when Acholeus transformed himself into a bull, Heracles took one of his horns. Acholeus offered him the horn of the goat Amalthaea, and Heracles in turn gave it to the Naiads who transformed the horn into the cornucopia)

Origin: Latin, cornu (horn) + copia (wealth)
Horn of wealth, taken to mean horn of plenty
In classical mythology, it was an infinite source of food and drink from the goat Amalthaea

And thus I wish you all a Happy Thanksgiving, and may it be filled with a cornucopia of food, family, and fun.

To expound upon my previous post regarding histology and pathology, there is an important step between conducting a biopsy and generating a diagnosis. The tissue in question must be “fixed” (preserved), sectioned (cut into slices), and stained [Origin: Old Norse steina (to paint)]. There are numerous stains and different ones are useful for different purposes. The classic stain that most students of histology are introduced to is the H&E stain. This stands for haematoxylin and eosin.

Origin: Greek, haima (blood) + xylos (wood)
Extracted from the logwood tree; depending on its preparation, its solution appears blood red

Origin: Greek, eos (dawn)
So named after the Greek goddess of the dawn, Eos, for its red/dawny color

To start, haematoxylin is oxidized into haematein and combined with aluminum ions. This forms the active dye-metal complex, and this complex is what binds to nucleic acids to stain nuclei and ribosomes purple. (The former contains DNA in the form of chromatin and the latter is composed of RNA.) It is thought that the highly negative phosphate backbone is what binds to the positively-charged haematein. We use the word basophilic [Gk. base + philia (love)] to refer to entities that bind to basic, i.e., positively-charged dyes. I will discuss the etymology of chemical terms such as “base” in a future post!


Eosin is used as the counterstain to haematoxylin. When eosin is dissolved in water or ethanol, its carboxylic acid and phenol are deprotonated to form a negative ion. This form of eosin binds to positively-charged entities such as the positive amino acids, e.g., arginine and lysine. Hence, the cytoplasm appears red because its proteins bind to the negatively-charged eosin. We use the word eosinophilic [Gk. eosin + philia (love)] to refer to entities that bind to acidic, i.e., negatively-charged dyes.

In the 1970s, the price of haematoxylin rose steeply, and it resulted in a search for a synthetic alternative. My schoolmate and former histology TA, Dr. Alexander Morgan, relayed an interesting aside to me: “European lust for haematoxylin based dye led to British logging in South America, and why there’s one tiny, mosquito-infested, swampy country in South America where they speak English [referring to Belize]. Many people died (dyed?) of malaria trying to harvest the wood to make the stain.”

These terms present a natural tie-in to immunology. There are two leukocytes that I am referring to: one is the eosinophil, which is colored quite intensely red, and the other is the basophil, which is colored quite intensely blue. I believe a picture is in order to better illustrate:

eosinophil basophil rev2

Another interesting stain is the silver stain. Camillo Golgi, a 19th-century Italian physician and Nobel laureate, developed silver staining to study the nervous system. (The cellular organelles known as Golgi bodies are named after him.) There are two classes of cells that take up silver: the argentaffins and the argyrophiles.

Origin: Latin, argentum (silver) + affinis (akin/affinity)
Affinity for silver; more specifically, cells that take up silver without a reducing agent

Origin: Greek, argyros (silver) + philia (love)
Love of silver; more specifically, cells that take up silver and need a reducing agent

There are various methods for preparing different silver stains. These stains can be used for a number of applications such as:

  1. Diagnostic microbiology (staining of fungi such as Pneumocystis jiroveci)
  2. Neuropathology (staining of neuritic plaques and neurofibrillary tangles in Alzheimer disease)
  3. Histology (staining of type III collagen and reticulin)

silver stains

Left: neurofibrillary tangles of Alzheimer disease. Right: membranous nephropathy

The last stain I will briefly touch upon is the periodic acid-Schiff (PAS) stain. This stains for polysaccharides, glycoproteins, glycolipids, and the like. Hence, it can be used to diagnose things like the glycogen storage diseases, adenocarcinomas (which often secrete mucin), Whipple’s disease, etc. The reason why I bring this up is that many people say it incorrectly. It is not periodic as in “recurring time intervals.” Rather, is per-iodic, i.e., of the periodiate ion (IO4)! Periodic acid oxidizes vicinal [L., vicinus (near)] diols to create a pair of aldehydes. These aldehydes then react with the Schiff reagent to produce a purple color.

When learning organic chemistry, one of the first topics presented is the naming of organic compounds. The International Union of Pure and Applied Chemistry (IUPAC) codified its recommendations in A Guide to IUPAC Nomenclature of Organic Compounds in 1900. Since then, it has been constantly revising its naming schema for both organic and inorganic compounds. Students of organic chemistry also learn the original nomenclature (“common” nomenclature) for some compounds and groups. First of all, what is the etymology of nomenclature?

Origin: Latin, nomen (name) + culator (one who calls; from calare, to call)
A calling by name

The IUPAC, for one- and two-carbon alkyl substituents, kept the original nomenclature. For the three- and four-carbon alkyl substituents, they modified them slightly. The rest of the substituents have new standard names, but in many instances, especially in biochemistry, the original names are kept. A few of these names beg for an etymological breakdown.

-CH3; methyl
Origin: Greek, methu (wine) + hule (wood)
Wood spirits/wood alcohol; methanol is a byproduct when destructively distilling wood

-C2H5; ethyl
Origin: Latin, aether (upper air) + -yl (shorter form of hule)
Back-named from (diethyl) ether, for its very low boiling point

-C3H7; propyl
Origin: Greek, pro– (first) + pion (fat) + –yl
First fat, from Dumas’s observation that propionic/propanoic acid is smallest carboxylic acid to display the properties of other fatty acids

linoleic acid revBonus: linoleic [Origin: Greek, linon (flax) + oleum (oil)]

-C4H9; butyl
Origin: Latin, butyrum (butter) + –yl
So named from the fact that rancid butter contains butyric/butanoic acid

-C5H11; pentyl
Origin: Latin, penta– (five) + -yl
Five carbons in the alkyl group

And starting with pentyl, the rest of the alkyl groups are named by Latin numbers. Sad…