50 Fun Facts About Amino Acids

Which amino acid is wrongly blamed for the drowsiness that follows a big Thanksgiving turkey dinner?

Tryptophan takes the blame, yet turkey holds about as much of it as any other poultry. The body does turn it into serotonin and the sleep hormone melatonin.

Which amino acid, identified in kelp broth by a Tokyo chemist, gives food its savory umami taste?

Glutamate is the G in MSG: Kikunae Ikeda crystallized it from kombu broth in 1908 and named its taste umami. Aged cheeses and soy sauce are naturally rich in it.

In Jurassic Park, the dinosaurs are engineered to die without supplements of which amino acid?

Lysine was the kill switch, known as the lysine contingency. Humans have no way of making it either, and simply get it from everyday foods such as eggs, meat and beans.

Which energy drink ingredient, a cousin of the amino acids, is named after the ox bile it came from?

Taurine comes from taurus, Latin for bull or ox, because two German scientists first isolated it from ox bile in 1827. Cats must get it from their diet, so it is added to cat food.

Diet sodas sweetened with aspartame carry a warning for people with PKU about which amino acid?

Phenylalanine is released as the body digests aspartame, and people born with phenylketonuria cannot break it down. Left unchecked it harms the brain, so many countries screen every newborn.

What did Stanley Miller pass through a flask of simple gases to create amino acids from scratch?

Electric sparks stood in for lightning in a mock early-Earth atmosphere, and amino acids formed. Sealed vials reopened after Miller's death in 2007 held even more of them than he had reported.

Which Google DeepMind AI system predicts a protein's 3D shape from its amino acid sequence alone?

AlphaFold won its makers Demis Hassabis and John Jumper a share of the 2024 Nobel Prize in Chemistry. Sixty years of lab work had solved about 170,000 protein shapes out of some 200 million known proteins.

Which protein, the most abundant in mammals, holds together skin, tendons, cartilage and bone?

Collagen makes up a quarter to a third of all the protein in a mammal's body. Its three chains twist into a rope so tight that every third amino acid has to be the smallest one available.

Which legume is a complete protein, supplying enough of all nine essential amino acids?

The soybean is unusual among plant foods in that respect, which is why tofu and soy milk can stand in for meat and dairy. Chickpeas and most other legumes run short of one essential amino acid.

Which hormone that drives labor contractions and milk release is a chain of just nine amino acids?

Oxytocin is so small that in 1953 it became the first hormone of its kind to be built from scratch in a lab, earning Vincent du Vigneaud a Nobel Prize. Doctors still use the synthetic form to induce labor.

Which amino acid, the first ever isolated, was crystallized from the juice of a spring vegetable?

Asparagine turned up in asparagus juice in 1806, in the hands of French chemists Louis Nicolas Vauquelin and Pierre Jean Robiquet. Heated with sugars during cooking, it forms the chemical acrylamide.

Which amino acid is the simplest of the 20, with just a single hydrogen atom for a side chain?

Glycine is also the only one of the 20 with no mirror-image twin, because its side chain is too plain to have one. Its name comes from the Greek for sweet, after the taste of its crystals.

Which amino acid forms the bridges in hair that a perm breaks and then rebuilds in a new shape?

Cysteine carries a sulfur-tipped side chain, and two of them can clasp together into a disulfide bridge. Perm lotion snaps those bridges, then a second lotion re-forms them around the curler.

Which amino acid is coded by AUG, the start signal that opens nearly every protein recipe?

Methionine is therefore the first link laid down whenever a cell begins building a protein. It is also one of only two amino acids spelled by a single genetic word; most have several.

Which amino acid is the only one of the 20 whose side chain loops back to bond with its backbone?

Proline's rigid five-membered ring makes it a structural disruptor, breaking up the neat spirals and sheets of a folded protein. It is named after pyrrolidine, the ring it contains.

Which amino acid, the body's raw material for dopamine, is named after the Greek word for cheese?

Tyrosine was discovered in 1846 by Justus von Liebig in casein, the main protein of cheese. The skin and hair pigment melanin is built from it too.

Which amino acid does the body turn into the allergy chemical that hay fever pills block?

Histidine loses a single carbon dioxide group to become histamine, the trigger for the sneezing, itching and hives of an allergy. Antihistamine pills blunt its effects.

Which amino acid do blood vessel walls convert into nitric oxide, the gas that relaxes arteries?

Arginine is the raw material for the gas, whose discovery as a blood vessel relaxer earned a 1998 Nobel Prize. Its name comes from the Greek for silver, after its silvery-white crystals.

Which branched-chain amino acid, abundant in whey, signals muscles to start building new protein?

Leucine flips on mTOR, a master switch for growth inside muscle cells, which makes it the star of BCAA supplements. Its name comes from the Greek for white, the color of its powder.

Which amino acid gives its name to ALT, the enzyme measured in routine blood tests of liver health?

Alanine aminotransferase, or ALT, is screened for because a raised level in the blood is an early flag for liver trouble. The amino acid itself was first made in a lab in 1850 and named in a nod to aldehyde.

Which element, absent from pure fats and carbohydrates, is found in every single amino acid?

Nitrogen sits in the amino group that gives these molecules their name. Food labs exploit that: they estimate how much protein a food holds by measuring how much of the element it contains.

Nine of the 20 standard amino acids are labeled essential for adult humans for what reason?

The body cannot make them, so they have to arrive ready-made in food. The other eleven are just as vital to life; our cells simply build those for themselves.

Which small molecule is released each time two amino acids join together in a growing chain?

Water is squeezed out as each link forms, which is why chemists call it a condensation reaction. Digestion runs the process in reverse, adding the molecule back to split proteins apart.

Which cell structure reads a genetic message and links amino acids together into a protein chain?

The ribosome of a bacterium differs enough from ours that some antibiotics kill germs simply by jamming theirs. Every living cell depends on these molecular machines.

What name do chemists give the link that joins one amino acid to the next in a protein chain?

A peptide bond forms when the acid end of one amino acid reacts with the amine end of the next. The name goes back to Emil Fischer, who proposed in 1902 that proteins are chains built this way.

In sickle cell disease, a one-letter gene change swaps which amino acid into hemoglobin?

Valine leaves an oily patch on hemoglobin where a charged amino acid used to be, and the molecules stick together into long stiff chains that bend the red cell into a crescent.

Which amino acid was first obtained from silk protein, and takes its name from the Latin for silk?

Serine was first obtained from silk in 1865 by Emil Cramer, and the fiber remains a particularly rich source of it. Its name comes from sericum, the Roman word for the fabric.

Which amino acid, the last of the 20 to be discovered, was found by nutrition chemist William Rose?

Threonine turned up in 1935, after Rose found that the 19 amino acids then known were not enough to sustain growth. The hunt let him map exactly which amino acids a diet must supply.

Which amino acid, a major fuel for intestinal cells, is the most abundant one free in human blood?

Glutamine also serves as the bloodstream's safe carrier for ammonia, ferrying the toxic waste away for disposal. Its one-letter code in protein sequences is Q.

Which tough structural protein makes up human hair and fingernails as well as rhino horn?

Keratin also builds feathers, claws, hooves and the outer layer of your skin. Even the slime threads of the hagfish, an eel-shaped sea creature, are made of it.

Which wobbly dessert ingredient is nearly pure protein yet lacks one essential amino acid entirely?

Gelatin is 98 to 99 percent protein when dry, but it has none of one essential amino acid and too little of three others, so it cannot serve as the only protein in a diet.

What is the term for a protein losing its folded shape, as when egg white turns solid in a hot pan?

Denaturation unravels a protein's folds but leaves the links between its amino acids intact, so the chain itself survives. It is why boiled eggs turn hard and cooked meat becomes firm.

Which organ, lined with finger-like villi, absorbs most of the amino acids from digested food?

The small intestine runs to about 6.5 meters in an adult and is called small only because it is narrow. Proteins have to be cut down to amino acids or tiny fragments before it can take them in.

When the body burns amino acids for fuel, the liver converts the toxic ammonia left over into what?

Urea is safe enough to ride in the blood to the kidneys, which flush it out in urine. In 1828 Friedrich Wöhler made it from inorganic ingredients, a milestone that blurred the line between living and lab chemistry.

Which hormone was the first protein to have its amino acid sequence worked out, by Frederick Sanger?

Insulin won Sanger the 1958 Nobel Prize in Chemistry and showed that every protein has one exact, definite order of amino acids. He took a second chemistry Nobel in 1980 for sequencing DNA.

What name is given to the three-letter genetic word that specifies a single amino acid?

A codon is three letters long, which gives 64 possible words for just 20 amino acids, so most amino acids can be spelled in several different ways.

Every amino acid carries an amino group at one end and which acidic group at the other?

The carboxyl group is the acid in amino acid: a carbon atom bonded to two oxygens. Fatty acids carry the very same group, which is why both families have acid in their names.

The simple order of amino acids along a protein chain is known as which level of structure?

Primary structure is just the sequence, written from one end of the chain to the other like a line of text. The higher levels describe how that line then coils, folds and teams up with other chains.

Which amino acid, not one of the 20 used to build proteins, was discovered in green tea leaves?

Theanine makes up about 1 to 2 percent of the dry weight of green tea leaves. It was discovered in 1949 and first isolated the following year from gyokuro, a Japanese green tea.

Which stomach enzyme, switched on by gastric acid, starts cutting food proteins into shorter pieces?

Pepsin was one of the first enzymes ever discovered, by Theodor Schwann in 1836, who named it from the Greek for digestion. It is released in an inactive form and only wakes up in acid.

Which molecule, folded like a cloverleaf, ferries each amino acid to a growing protein chain?

Transfer RNA reads the genetic message at one end and holds the matching amino acid at the other, making it the cell's translator. Francis Crick predicted such an adaptor before anyone had found one.

Which term describes an amino acid carrying both a positive and negative charge yet neutral overall?

Zwitterion borrows the German word Zwitter, meaning hermaphrodite, for a molecule that is two things at once. The acid end hands a hydrogen ion to the amino end, leaving one charge of each sign.

Which chemist, later a Nobel Peace laureate, worked out the alpha helix that proteins coil into?

Linus Pauling found the spiral in 1948 while in bed with a cold, by sketching a chain of amino acids on a strip of paper and folding it. He is the only person to win two unshared Nobel Prizes.

NASA's OSIRIS-REx probe returned samples holding 14 of life's 20 amino acids from which asteroid?

Bennu's amino acids came as an even mix of mirror-image forms, whereas living things on Earth use just one of the two. The capsule of asteroid dust landed in the Utah desert in September 2023.

Which letter labels the mirror-image form of amino acids that living things use to build proteins?

The L form, often described as left-handed, is the one built into the proteins of every known organism. Its mirror twin does turn up in nature, in bacterial cell walls and some antibiotics.

Which letter do chemists use as shorthand for the side chain that makes each amino acid different?

R stands in for anything from a lone hydrogen atom to a bulky double ring, and it alone sets each amino acid's character. The symbol dates from the 19th century and echoes words such as residue and radical.

Which single letter stands for aspartic acid in the one-letter code used to write protein sequences?

D was assigned arbitrarily, and students remember it with the mnemonic asparDic acid. The obvious first letter had already gone to a smaller, simpler amino acid.

In the one-letter code for protein sequences, which letter stands for any or an unknown amino acid?

X is the placeholder for a position whose amino acid is unknown or does not matter. Anyone used to genetics may be tempted by N, which plays the same wildcard role in DNA sequences.

Which weedkiller, sold as Roundup, kills by blocking the pathway that makes three amino acids?

Glyphosate jams the shikimate pathway, which exists in plants and microbes but not in animals. Crops engineered to tolerate it can be sprayed and survive while the weeds around them die.

Which giant muscle protein, one chain of roughly 34,000 amino acids, acts as a molecular spring?

Titin is named after the Titans of Greek myth, and its full chemical name is the longest of any protein. Each molecule is over a micrometer long and gives muscle its passive stretchiness.