Metabolism, Anabolism, and Catabolism

Metabolism is the breaking down of energy into different forms, which makes it possible for us to live our lives most productively: metabolism allows us to grow, to reproduce, and to respond to our surroundings.

Metabolism at its heart is made up of two processes: catabolism and anabolism. Catabolism the breaking down of substances to get back to their building blocks. Once we’ve broken down things, we want to create something useful out of them — this is anabolism.

One way to think about it is a Lego analogy. If someone has a construction made of Legos and you want to turn it into something else, you would use catabolism to break up the Lego construction into individual Lego pieces, and later use anabolism to take these individual pieces and create a new shape.

Our most direct source of energy for life on Earth is the Sun. Originating in fusion reactions, the energy of the sun makes its way to the Earth through sunlight. Using a process called photosynthesis, plants take this energy and construct a material out of it that is accessible to human beings, and would eventually end up providing energy to us. The material in plants originates in the fixing of carbon. Carbon dioxide from the air is taken by the plants and turned into solid forms through bonding, to create molecules like glucose and cellulose. Plants also contain water and nutrients from the earth. From there, other living organisms will eat the plants and metabolize the energy in their own way. The organism will catabolize the molecules it has consumed, later to anabolize them to create the form of a cow, or a chicken, or a pig. What kind of materials is the organism catabolizing and anabolizing? It could be molecules such as carbohydrates, including simple sugars, polysaccharides, or starches. It could also be lipids, such as fatty acids or cholesterol. It could be proteins, made up of amino acids, which will be built up into new proteins. All of these molecules are contained in the food we eat, from vegetables to starches to meats, which we will then catabolize and anabolize —at the end of the day, this provides the structures of our bodies, and the energy we make use of to live our lives every day. It is so mindblowing to think about where our energy comes from: it turns out that when you go for a run, the energy that makes it possible for your legs to move did not only come from a good night’s rest, but from the molecular fusions of elements in the stars above!