Body Chemistry Decoded

Body Chemistry: Your body runs on four families of molecules. Proteins do the work, carbohydrates supply fuel, lipids store energy and build cell walls, and nucleic acids (DNA and RNA) hold the instructions. Amino acids build proteins, some proteins act as enzymes that speed up reactions, and some act as hormones that carry messages. Learn those links and most health and nutrition talk suddenly makes sense.

Amino Acid: The 20 standard amino acids are the alphabet that every protein is spelled with. Your body can make 11 of them, but 9 are called essential because they must come from food. One of them, glutamate, is the reason savory foods taste like umami.

Peptide: A peptide is just a short chain of amino acids, usually under about 50 links. Past that it gets called a protein. Oxytocin, the so called bonding hormone, is a peptide only 9 amino acids long.

Protein: A protein is a long amino acid chain that folds into a precise 3D shape, and the shape decides the job. The largest human protein, titin, is roughly 34,000 amino acids long and acts like a molecular spring inside your muscles.

Enzyme: An enzyme is a protein that speeds up a chemical reaction without getting used up. Most names end in "ase" (lactase breaks down lactose). One reaction that enzymes finish in milliseconds would take about 78 million years on its own.

Lock and Key Model: In 1894 Emil Fischer proposed that an enzyme fits its target molecule like a key in a lock. In 1958 Daniel Koshland refined it with induced fit: the lock actually flexes and reshapes itself around the key.

Denaturation: When heat or acid unravels a protein's shape, it stops working. That's what happens when an egg white turns from clear to solid, and it's one reason a very high fever is dangerous.

Coenzyme: Many enzymes can't work alone and need a small helper molecule called a coenzyme. Most B vitamins exist to become coenzymes, which is why you only need them in tiny amounts but get sick without them.

Hormone: A hormone is a chemical messenger released into the blood to change what distant cells do. The word was coined in 1905 by physiologist Ernest Starling, from a Greek word meaning "to set in motion."

Insulin: Insulin is a hormone that is also a protein, made by the pancreas to pull sugar out of the blood. It was the first protein ever fully sequenced, earning Frederick Sanger the 1958 Nobel Prize.

Steroid Hormone: Not all hormones are proteins. Testosterone, estrogen, and cortisol are built from cholesterol, which lets them slip straight through cell walls and switch genes on or off from inside the cell.

Adrenaline: Adrenaline and epinephrine are the exact same molecule; the British use one name and Americans the other. In 1901 Jokichi Takamine made it the first hormone ever isolated in pure form.

Neurotransmitter: A hormone travels through blood to the whole body, while a neurotransmitter jumps a tiny gap between two nerve cells. Otto Loewi proved chemical signaling between nerves in 1921 with a frog heart experiment he said came to him in a dream.

Receptor: A receptor is a protein on or inside a cell that a messenger plugs into, like a key into an ignition. About a third of all approved drugs work by targeting one receptor family called G protein coupled receptors.

Metabolism: Metabolism is the total of every chemical reaction in your body. It has two halves: catabolism breaks things down for energy, and anabolism builds things up, like muscle.

ATP: ATP is the energy currency every cell spends. You only hold about 250 grams at a time, yet you recycle roughly your own body weight in ATP every single day.

Glucose: Glucose is the simple sugar your cells burn for fuel. Your brain is about 2 percent of your body weight but uses around 20 percent of its energy, mostly from glucose.

Glycogen: Glycogen is how your body stockpiles glucose, mostly in the liver and muscles. When marathon runners "hit the wall" around mile 20, it's usually because their glycogen tank has run dry.

Lipid: Lipids are the molecules that don't mix with water: fats, oils, waxes, and cholesterol. Fat packs 9 calories per gram versus 4 for protein or carbs, which is why the body uses it for long term storage.

Cholesterol: Cholesterol is essential for building cell walls and steroid hormones, and your liver makes most of it. LDL and HDL, the "bad" and "good" kinds, aren't actually cholesterol; they're protein carriers that ferry it through the blood.

Gene: A gene is a stretch of DNA holding the recipe for one protein. Humans have only about 20,000 protein coding genes, fewer than a grapevine.

Ribosome: The ribosome is the cell's protein factory, reading genetic instructions and snapping amino acids together. Its core work is done by RNA, not protein, a discovery that won the 2009 Nobel Prize in Chemistry.

Antibody: An antibody is a Y shaped protein that tags invaders for destruction. By shuffling gene pieces, your immune system can produce billions of different antibodies, enough to match germs it has never met.

Collagen: Collagen is the most abundant protein in your body, about 30 percent of the total, holding together skin, bones, and tendons. Gelatin in Jell-O is simply collagen that has been boiled.

Hemoglobin: Hemoglobin is the iron containing protein that carries oxygen and makes blood red. Each red blood cell holds about 270 million of them, and Max Perutz spent 25 years mapping its structure for a 1962 Nobel Prize.