50 Fun Facts About Macromolecules

Which carbohydrate, the most abundant organic polymer on Earth, makes up 90% of cotton fibre?

Cellulose passes through the human gut undigested as dietary fibre. Cows and termites can live on it only because microbes in their guts break it down for them.

Which protein, the most abundant in the bodies of mammals, takes its name from the Greek word for glue?

Collagen turns into gelatin when skin, bones and sinews are boiled, which is how animal glue was made for centuries. It accounts for 25% to 35% of a mammal's protein.

Which tough protein builds human hair and fingernails as well as rhino horns and bird feathers?

Keratin gets its strength from sulfur cross-links between its chains, which is why burning hair smells so sharp. The same protein makes hooves, claws and wool.

Which protein network in wheat flour traps gas bubbles and gives bread dough its stretch and chew?

Gluten forms when two wheat proteins, gliadin and glutenin, are wetted and kneaded. It is also the base of seitan, the mock meat sold as vegetarian duck and chicken.

Which shape did James Watson and Francis Crick propose for the DNA molecule in their Nobel Prize-winning model?

Double helix became a household phrase after Watson used it as the title of his 1968 memoir. The two strands wind around each other like a twisted ladder.

Which hormone, made by beta cells in the pancreas, became the first protein ever to be fully sequenced?

Insulin takes its name from the Latin for island, after the clusters of pancreas cells that make it. It tells the body's cells to take up sugar from the blood.

Which natural fibre, made mostly of the protein fibroin, turned up in 8,500-year-old tombs in China?

Silk is about 75–80% fibroin, wrapped in a gummy protein called sericin that is boiled off before reeling. A whole cocoon can be unwound as one continuous thread.

Which synthetic polymer from DuPont was sold as toothbrush bristles before it caused a rush for stockings?

Nylon stockings sold 64 million pairs in their first year on the market. The first 4,000 pairs offered in Wilmington, Delaware, were gone within three hours.

Which iron-containing protein fills red blood cells and carries oxygen from the lungs to the body's tissues?

Hemoglobin makes up about 96% of a red blood cell's dry weight. Each molecule is built from four protein chains and can carry up to four oxygen molecules at once.

Which tough carbohydrate forms both the outer shells of insects and crabs and the cell walls of mushrooms?

Chitin is the second most abundant polysaccharide in nature, with about a billion tons made each year. Squid beaks are built from it too.

Which simple sugar, made by plants during photosynthesis, circulates in human blood as blood sugar?

Glucose is the most abundant simple sugar in nature, and every living organism can use it for energy. Its name comes from the Greek for sweet.

Which carbohydrate do green plants make to store energy, filling staples such as potatoes and rice?

Starch is the most common carbohydrate in the human diet. Wheat, maize and cassava are packed with it too, which is why it feeds most of the world.

Which branched carbohydrate do humans store in the liver and muscles as a quick reserve of energy?

Glycogen makes up 5–6% of the liver's fresh weight, roughly 100–120 grams in an adult. The skeletal muscles hold about 400 grams more.

Which sugar, refined from sugarcane and sugar beet, is the chemical name for ordinary white table sugar?

Sucrose makes up about a fifth of a sugar beet root by weight. Each molecule is two simple sugars joined together, which the gut has to split apart.

Which sugar in milk causes bloating in adults who no longer make the enzyme needed to digest it?

Lactose makes up around 2–8% of milk by mass. Most mammals stop making the enzyme that splits it after weaning, so digesting milk as an adult is the unusual trait.

Which fatty substance, first found in gallstones, is the raw material for vitamin D and the sex hormones?

Cholesterol got its name from the Greek for solid bile, because it was first identified in gallstones in 1769. Every animal cell also builds it into its outer membrane.

Which kind of fat, solid at room temperature in butter and lard, has chains with no double bonds?

Saturated fats also turn up in a few plant foods, notably coconut oil and palm kernel oil. Their straight chains pack closely, while a double bond bends a chain and keeps oils liquid.

Which lipids do plants secrete onto the surface of their leaves to control evaporation and shed rain?

Waxes are also what bees secrete to build honeycomb. They shed water so well that people use them in polishes, candles and waterproof coatings.

Which building blocks of proteins include nine essential kinds that the human body cannot make?

Amino acids come in more than 500 kinds in nature, yet only 22 are ever built into proteins. The last of the 20 common ones, threonine, was not discovered until 1935.

Which natural polymer of isoprene is collected as milky latex by cutting the bark of a tropical tree?

Rubber was first used by the Olmec of ancient Mexico, who made balls from it for the Mesoamerican ballgame. Each of its chain molecules can weigh up to a million daltons.

Which Y-shaped proteins does the immune system release to recognise and neutralise bacteria and viruses?

Antibodies each bind to one particular target, and the body can make a variety to match almost any shape. The word antigen is usually explained as short for antibody generator.

Which type of RNA, used in the Pfizer and Moderna COVID-19 vaccines, carries a gene's instructions for a protein?

Messenger RNA was given its name by François Jacob and Jacques Monod, and its existence was shown in 1961. In a vaccine it has a person's own cells make a harmless piece of a virus.

Which chemist oversaw the DNA X-ray image Photo 51 yet died four years before its structure won a Nobel Prize?

Rosalind Franklin died of ovarian cancer in 1958, aged 37. The photograph was taken by her PhD student Raymond Gosling, and it was the 51st diffraction image he had made.

Which element, dripped onto bread or potato in a classic school food test, turns the food blue-black?

Iodine slips inside the coiled amylose chains in such foods, and the trapped molecules look blue-black. Counterfeit-detector pens use the same reaction on wood-pulp paper.

Which process, triggered by heat or acid, unfolds a protein and turns a raw egg white solid and opaque?

Denaturation scrambles a protein's folded shape but leaves the chain itself unbroken. It is why cooked meat turns firm and why a boiled egg stays solid after it cools.

Which infectious agents, misfolded proteins carrying no genes at all, cause mad cow disease in cattle?

Prions spread by making normal copies of the same protein misfold in turn. Stanley Prusiner built the name from protein and infection, and won a 1997 Nobel Prize.

Which particle, itself built of RNA and protein, assembles every protein that a living cell makes?

Ribosomes were first seen in 1955 by George Palade and were at first called Palade granules. The part that actually joins the chain together is RNA, not protein.

Which element do food labs measure to gauge protein content, since fat and carbohydrate contain none?

Nitrogen stands in for protein so reliably that fraudsters exploit it. In China's 2008 milk scandal, melamine was added to watered-down milk to fool the test.

What are the small molecules called that join end to end by the thousand to form a polymer?

Monomers get their name from the Greek for one part. A chain may repeat a single kind, as most plastics do, or mix several kinds, as proteins and DNA do.

Which molecule, the energy currency of cells, do people recycle at a rate of their own body weight each day?

ATP is built like a single link of an RNA chain with two extra phosphate groups attached. An average adult turns over around 50 kilograms of it every day.

Which type of reaction do digestive enzymes use to split proteins, fats and carbohydrates into small units?

Hydrolysis spends one molecule of water on every bond it breaks, undoing the reaction that built the chain. Soap-making is the same chemistry applied to fat.

Which reaction, also called condensation, links small units into proteins, fats and nucleic acids?

Dehydration synthesis is named for the molecule of water removed each time a new link is made. Digestion runs the same reaction backwards, putting the water back.

Which molecules, each with a water-loving head and two water-fearing tails, form the double layer of cell membranes?

Phospholipids line up tail to tail in water all by themselves, which is how a membrane can assemble without instructions. The first one identified came from chicken egg yolk in 1847.

Which covalent link joins one building block to the next along the backbone of every protein chain?

Peptide bond formation releases one molecule of water for each link added. The finished bond is rigid and flat, which limits the ways a protein chain can fold.

Which level of protein structure is simply the linear order of the units in the chain, as set by a gene?

Primary structure decides everything after it, because the order of the units dictates how the chain folds. A single swapped unit in one blood protein is enough to cause sickle cell disease.

Which enzyme in human saliva makes rice or potato taste sweeter the longer a mouthful is chewed?

Amylase launched the science of enzymes when French chemists isolated it from sprouting barley in 1833. In some old brewing methods the grain is chewed to set it working.

Which building blocks of DNA and RNA are each made of a sugar, a phosphate group and a base?

Nucleotides do more than build genes. Loose ones carry energy around the cell and pass signals between its parts.

Which base takes the place of thymine when a cell copies a stretch of DNA into RNA?

Uracil pairs with adenine exactly as thymine does. Cytosine can decay into uracil by accident, so cells treat any uracil found in DNA as damage and cut it out.

Which weak attractions hold the two strands of DNA together, two between A and T and three between G and C?

Hydrogen bonds are easy to break and re-form, so the two strands can be pulled apart like a zipper for copying. Heat alone is enough to separate them.

Which pocket on an enzyme, shaped to fit one particular molecule, is where the substrate binds and reacts?

Active site space takes up only about 10–20% of an enzyme's volume, yet it is where all the chemistry happens. The rest of the molecule holds it in exactly the right shape.

Which three-letter unit of the genetic code tells a cell which building block to add next to a protein?

Codon combinations number 64, far more than the 20 or so building blocks they specify, so most are spelled several ways. Three of them simply mean stop.

Which American chemist, the only winner of two unshared Nobel Prizes, showed in 1951 how protein chains coil?

Linus Pauling won the Chemistry prize in 1954 and the Peace prize in 1962. The coil came to him in 1948 while he lay in bed with a cold, folding a paper sketch of a chain.

Which everyday image did chemist Emil Fischer use in 1894 for the exact fit between an enzyme and its target?

Lock and key implied a rigid fit, and the picture held for decades. In 1958 Daniel Koshland revised it, arguing that a flexible enzyme is reshaped as it grips its target.

Which classic school lab check for protein uses copper ions that turn a food sample purple?

Biuret test reagent contains no biuret at all, despite the name. Its copper ions bind to the links between the units of a protein chain, so more protein gives a deeper colour.

Which proteins act as spools that DNA winds around, packing nearly two metres of it into each human cell?

Histones carry a positive charge that grips the negatively charged backbone of DNA. They were discovered in 1884, decades before anyone knew that DNA carries heredity.

Which German chemist won a 1953 Nobel Prize for showing that long-chain giant molecules, or macromolecules, exist?

Hermann Staudinger faced years of doubt, as most colleagues refused to accept that small molecules could link into chains of such size. He also founded the first polymer chemistry journal.

Which doctor first isolated DNA, in 1869, from white blood cells washed out of pus-soaked hospital bandages?

Friedrich Miescher named his find nuclein, after the cell nucleus it came from. Its importance was not clear at first, and he went on to study it in salmon sperm.

Which British biochemist won two Nobel Prizes in Chemistry, for sequencing a protein and then DNA?

Frederick Sanger turned down a knighthood because he did not want to be called Sir. He is one of only a handful of people ever to win two Nobel Prizes.

Which Swedish chemist is credited with originating the terms protein, polymer, catalysis and isomer?

Jöns Jacob Berzelius proposed protein in 1838, from a Greek word for first, because the substance seemed so fundamental to life. The letter symbols used for the chemical elements were his invention too.

Which giant muscle protein has a full chemical name of 189,819 letters, sometimes called the longest English word?

Titin works as a molecular spring that gives muscle its passive stretch. Its human form is a single chain of 34,350 units, more than a micrometre long.