A simple sugar. Several of these attached make a polysaccharide, like starch.
The little balls represent amino acids. Those attach, the chain curls up, and the final result is a functional machine.
The four railroad cars of DNA are guanine, cytosine, thymine, and adenine. The order of these determines what the DNA says.
Types of lipid
In my last chemistry blog post, I wrote about how atoms combine into small molecules, making things like salt (via ionic bonds), methane (via electron sharing or covalent bonds), and water (via a combination of the two, called polar covalent bonds). I ended with a promise to explain how highly organized macromolecules are the backbone of all life. All of it! From tiny bacteria to huge dinosaurs.
To start, remember carbon? That atom that has four outer shell electrons, wants eight, and shares with other atoms to get them? It has a unique feature: it can share three electrons with another atom, two with two others, or one with four others. This means it can form an endless number of organic (carbon-containing) compounds.
To orient you to the diagrams, since carbon is always part of life molecules, it’s designated not with a “C” but just as a corner in the diagram. “O” means oxygen, and H means hydrogen.
The essential macromolecules fall into four categories: carbohydrates, proteins, nucleic acids, and fats. And you always thought three of those were foods! They are, but only because we eat plants and animals and those were alive.
Carbohydrates
This class of macromolecule is mostly made of sugars: 4-6 carbons with various oxygens and hydrogen atoms attached. To form the macromolecule, the sugars are lined up and attached like railroad cars. One unattached six-carbon carbohydrate is blood sugar (glucose); another is fruit sugar (fructose). If two cars are attached, they make a disaccharide: table sugar. And if a whole bunch of glucoses are attached in a long chain, you could get starch or plant fiber, depending on how they are attached. In life, the short carbohydrates are used for quick energy, and the longer “trains” for structure and energy storage. Believe it or not, carbohydrates are also used as cellular “words.”
Proteins
Did you know that cells contain a city full of complex machines? The machines are made of protein, which is why protein structure is complicated. However, it starts pretty simply with an amino acid, a carbon-based molecule. Actually, there are 20 kinds of amino acids, but they all attach in the same way—like railroad cars! These railroad cars have weird and wonderful chains hanging off them. This allows the “train” to coil up and attach to other trains and more. Eventually, proteins form the basis of all the different types of machines found in life. So next time you have a steak, remember, you’re eating machinery so that your body can cannibalize the parts to make your own machines.
Nucleic Acids
Recently, Amazon delivered a cart to my door. Well, they delivered pieces of a cart and instructions for how to put it together. The same is needed for a cell to make its machines: instructions. Those instructions are made of nucleic acids. DNA is the repository of all information for living beings. RNA is the middleman or blueprint, taking the instructions for how to make a machine from the head office to the factory floor, as it were. When the relatively simple structure of DNA was first ascertained, scientists didn’t believe it could be where inheritance was based because it consists of only four types of railroad cars. But it is. The information is contained in the sequence of those cars, like the information in a book is contained in the order of the sequence of letters. Incredible, but true! How this information gets read will be a topic for another time.
Lipids
The final type of macromolecule is lipids. Here, the structure is not like a train, but contains long chains of carbons and hydrogens, making the fats or lipids repel water. This is vital for cell membranes because only hydrophobic interactions hold them together. Think of a bottle of vinegar and oil. See how it quickly separates again? Yup. That’s how your cells are held together, too. Incidentally, cholesterol, estrogen, and testosterone also fall into this class.
Life
It’s so amazingly complex, simple, and organized. And macromolecules prove it!