Carbohydrates, Proteins, Nucleic Acids, And Lipids: The Four Biomolecules Of Life

An image showing the four major types of biomolecules essential for life.

If you were to zoom into the palms of your hand right now, small enough to peek inside your cells, you wouldn’t find a tiny factory floor with little hard-hat-wearing workers assembling your life’s mechanisms—though that would be quite cool. Rather, you would see chains of molecules working hard while interacting with each other to help you perform the actions that control your daily life. These molecules, which are carbohydrates, proteins, nucleic acids, and lipids, are the four major types of biomolecules: they store energy in your cells, carry important genetic information, make you stronger, and do everything else that makes life possible.

First, we have carbohydrates. They are often referred to as “sugars” or “carbs,” which sometimes gives them a bad reputation. However, if carbohydrates didnt exist, your body would struggle, since they are its primary and preferred source of energy. Carbohydrates are always made of carbon, hydrogen, and oxygen. Sometimes, they also have phosphorus and sulfur attached. If you carbohydrates represented as a diagram, they’re oftentimes shaped like a pentagon or a hexagon, with each unlabeled vertex serving as a carbon atom.

Glucose, galactose, and fructose, which are monosaccharides, are the basic building blocks of all other carbohydrates. When you combine two of them together through a glycosidic linkage, you make a disaccharide, usually seen in the form of sucrose or lacrose. String together even more monosaccharides, and you get polysaccharides like starch, glycogen, or cellulose. Monosaccharides, disaccharides, and polysaccharides are all forms of carbohydrates.

Carbohydrates have two main jobs: energy storage and structure. Polysaccharides serve to store energy in both animals and plants; plants store energy as starch, while animals use glycogen, and they both serve as quick, replinishable energy sources. Furthermore, polysaccharides also serve as a way to build structure in cell walls. Cellulose, a polysaccharide, gives plant cell walls their strength and rigidity. Similarly, chitin, a carbohydrate, makes up insect exoskeletons.

An enlarged visualization of the four main protein structures (via thoughtco.com).

Next off, we have proteins. Unlike carbohydrates, proteins serve more diverse and numerous functions within your body, including acting as enzymes, hormones, antibodies, transporters, and scaffolds. Proteins are made of amino acids, each with a carboxyl group, which is acidic; an amino group, which is basic; and an R group, which is a side chain. Proteins have four main structures that define how they function. The primary structure is the polypeptide chain, a linear, unique sequence of amino acids linked together in a chain by peptide bonds. Then, we have the secondary structure, which is when the primary structure is folded into either alpha helices or beta sheets, and its structure is held by hydrogen bonding. Next, we have the tertiary structure, which is the full 3D folding of a single polypeptide chain due to R-group interactions. This kind of structure is held together by ionic bonds, hydrogen bonds, van der Waals forces, or even disulfide bridges. Lastly, we have the quaternary structure, with multiple polypeptide chains coming together into a functional protein like hemoglobin.

Although the amino acids that make up proteins are what enable them to serve such a wide array of purposes, they also come with some drawbacks. The main one is that even switching one amino acid with another can change everything about the protein, and more importantly, how certain parts of your body function. Sickle cell anemia is a famous example of this, where one substitution alters the shape and function of hemoglobin. The structure and contents of a protein define how it functions, which is why so much time and energy is spent in your body to ensure they’re folded just right.

While proteins are out doing the work, nucleic acids serve as their blueprints. There are two main types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both of them are made of nucleotides, which are the building blocks of nucleic acids. Nucleotides consist of a five-carbon sugar, a phosphate group, and a nitrogenous base.

Albeit the similarities, there are a couple difference between DNA and RNA that set them apart from each other. The first one has to do with their sugars. In DNA, the sugar is deoxyribose, and the bases attached to it are adenine (A), thymine (T), guanine (G), and cytosine (C). On the contrary, in RNA, the sugar is ribose, and instead of thymine, there’s uracil (U).

The nucleotides connect in a long sugar-phosphate backbone, with the bases sticking out. DNA’s bases pair up via hydrogen bonds. A always pairs with T and G always pairs with C to form DNA’s double helix shape with two strands. RNA, however, is usually single-stranded and does not form a double helix shape.

A diagram illustrating the structural and compositional differences between DNA and RNA.

The difference between DNA and RNA is further driven in the way they function. DNA stores genetic information and acts as the cell’s instruction manual on how to build proteins, which perform most of the body’s dunctions. Messenger RNA copies and delivers the instructions to the cell’s ribosomes, which are resposible for making the proteins. Transfer RNA delivers the necessary amino acids, as per the instructions, to the ribosomes, and ribosomal RNA helps build the actual proteins.

Lipids, although negatively associated with fat, clogged arteries, and heart attacks, are critical for life as well. They form membranes, store energy, and signal between cells. Lipids come in several varieties: fats (triglycerides), phospholipids, and steroids. Triglycerides are made up of one glycerol and three fatty acids, and they are great for long-term energy storage and thermal insulation. Phospholipids are just like triglycerides, but a phosphate group replaces one of the fatty acids. They form the cell membrane’s phospholipid bilayer and consist of a hydrophilic, polar head facing outward and two hydrophobic, nonpolar tails tucked inward. Steroids, such as testosterone and estrogen, are ring-shaped lipids that serve as hormones and signaling molecules. Lipids also have differences in their structure, and they’re classified as either saturated or unsaturated, depending on the type of chemical bonds in their fatty acid chains. Saturated fats have no double bonds between carbons, meaning that they can stay solid at room temperature. On the other hand, unsaturated fats have double bonds, which means their chains are rigid and hard, making them liquid at room temperature.

From hemoglobin to muscles to tasting food, these four organic molecules—carbohydrates, proteins, nucleic acids, and lipids—are not just simple chemicals; they have defined, define, and will define our biological processes. Carbohydrates, proteins, nucleic acids, and lipids, depending on the molecule, serve as tools, building blocks, energy sources, and instructions for our cells, and their interactions are resposible for the life you are living right now!