What makes it possible for you to read this and to process it? Indeed, what makes it possible for you to open your eyes in the morning, become aware of your surroundings, get out of bed, remember where you left off yesterday, and do anything and everything you do?
Energy! You could say that. But how come you have the energy to do these things. How come you are alive today? It’s all thanks to metabolism. But what is metabolism and how does it happen?
What Is Metabolism?
The term metabolism can be confusing with many people thinking of it as the process of breaking down food to produce energy. While this is not far from it, metabolism is a lot more than that.
Metabolism is the collection of biochemical processes that take place within every cell of a living organism to produce energy and synthesize the resources necessary for the many functions carried out within the cell and the organism as a whole. The complex of processes relies on various raw materials and biological machinery at the site where the processes take place.1)
As previously mentioned, metabolism occurs in every cell of every living organism, both plant and animal. The processes have many similarities in plants and animals. However, in many plants, in addition to metabolism, another process called photosynthesis also occurs in which external energy from the sun is used to synthesize carbohydrate from carbon dioxide and water.
For the purposes of this discussion, we will focus on metabolism in animals, and more so in humans.
Metabolism vs Digestion
To carry out the processes constituting metabolism, the cells require some raw materials. These come in the form of nutrients and components of nutrients derived from the food we eat. This is probably the reason why many people confuse digestion for metabolism. But digestion is the process of breaking down food into the constituent components which include glucose, amino acids, vitamins, and minerals.
On the other hand, metabolism involves the use of these nutrients together with oxygen to produce energy, and to synthesize materials that are necessary for continued living. It is apparent that the digestive system is the means by which the raw materials for metabolism are processed for onward transmission through the bloodstream, to the sites where metabolism takes place.
Where Does Metabolism Take Place?
The machinery that makes metabolism possible is located inside the cells. This machinery comprises the physical infrastructure where the biochemical reactions occur, and the biochemicals necessary for the reactions to take place. The physical sites where this happens is mainly within organelles called mitochondria within cells.
The mitochondria have specialized compartments where different aspects of metabolism occur. It is worth to note that besides production of energy, metabolism also involves the synthesis of different proteins and other materials that form the physical structures that ensure the sustenance of life of every living organism.
When Does Metabolism Happen?
As you may have realized by now, metabolism is not an event that happens at a particular time. The processes that constitute metabolism are constantly happening in every cell in the body. Indeed, every cell in the body is like a complex of factories carrying out different manufacturing processes, and operating every minute of the day and night. These metabolic processes are extremely important because they produce the energy and resources that all tissues and organs need to provide the support necessary for the organism to remain alive.
Note that besides producing resources for maintenance of cells, tissues and organs; old or damaged cells are continually broken down to maintain the efficiency of the body and its systems. For this reason, metabolism also synthesizes the necessary materials to produce new cells and repair tissues.
How Metabolism Works
The purposes of metabolism are:
- Production of energy for use by the cell and the organism as a whole
- Synthesis of building blocks for tissues of the body in the forms of proteins, some carbohydrates, lipids, and nucleic acids
- Elimination of waste from the body
These metabolic processes don’t happen in all types of cells. However, production of energy by breaking down of glucose in the presence of oxygen, happens in all cells of the body.
The same is true of elimination of waste. This is because every cell requires energy, and the elimination of waste for it to function efficiently. Other metabolic processes are carried out by specialized cells in organs such as the liver, the pancreas, the spleen and the kidneys.
The Metabolic Processes
Metabolic processes are categorized as catabolic or anabolic.
In catabolic reactions, large molecules are broken down into smaller molecules. For instance, breaking down of glucose by way of cellular respiration, to produce energy and carbon dioxide.
In anabolic reactions, small molecules combine to make larger molecules. For instance, the building up or synthesis of proteins, lipids and nucleic acids. Anabolism is the process by which various materials needed by the cells and the body are synthesized.
In both categories of metabolic reactions, energy is involved. However, while anabolic reactions consume energy; catabolic reactions produce energy.2)
Metabolic reactions; whether anabolic or catabolic, follow certain pathways by which a series of changes occur. These pathways occur in both anabolic and catabolic reactions, and involve multiple steps, each catalyzed by an enzyme. For instance, breaking down of glucose to produce energy, also called glycolysis, is a 10-step process.3)
Both catabolic and anabolic reactions take place within the cells. The type of reaction that takes place at a particular time depends on the needs of the cell. If for instance, there is a high amount of glucose within a cell, some of it will be converted to storable forms such as glycogen and fat. This is a case of an anabolic reaction.
On the other hand, if there is a shortage of glucose in a cell, glycogen or even fat is broken down to produce energy in a catabolic reaction.
This can explain why sustained reduction in carbohydrate intake can lead to loss of stored body fat. It can also explain why high carbohydrate intake leads to increased body fat.
An Important Resource for Survival
Metabolism is the totality of critical processes by which every cell and every living organism gets the energy and other resources it requires for survival. In other words, without metabolism, a living cell will die. By extension, if metabolism stops in a majority of the cells forming a living organism, the result would be death.