Cells are the smallest units of living things that boast all of the properties associated with life. One of these defining characteristics is metabolism, or the use of molecules or energy gathered from the environment to carry out the biochemical reactions required to remain alive and, ultimately, reproduce.
Metabolic processes, often termed metabolic pathways, can be divided into those that are anabolic, or that involve the synthesis of new molecules, and those that are catabolic, which involve the breakdown of existing molecules.
Colloquially, anabolic processes are about building a house and replacing things like windows and gutters as needed, and catabolic processes are about taking worn-out or broken pieces of the house to curb. If these are done in concert at the right pace, the house will exist in as steady a state as possible, but never passively.
Overview of Metabolism
Cells and the tissues they form are continually undergoing "bidirectional" metabolism, meaning that while some things are flowing in an anabolic direction, others are going in the opposite direction.
This is perhaps more evident at the level of whole organisms: If you are burning through glucose while sprinting to catch up with your dog (catabolic process), the paper cut on your hand from the day before continues to heal (anabolic process). But the same dichotomy is at work in individual cells.
Cellular reactions are catalyzed by special globular protein molecules called enzymes, which by definition participate in chemical reactions without being changed themselves in the end. They greatly speed up reactions – sometimes by a factor of well over a thousand – and thus function as catalysts.
Anabolic reactions usually require an input of energy and are therefore endothermic (loosely translated, "heat to the inside"). This makes sense; you can't grow or build muscle unless you eat, with your food intake usually scaling to the intensity and duration of a given activity.
Catabolic reactions are usually exothermic ("heat to the outside") and liberate energy, much of which is harnessed by the cell in the form of adenosine triphosphate (ATP) and used for other metabolic processes.
Substrates of Metabolism
The main structural elements of the body and the molecules it requires for fuel plus tissue growth and replacement are composed of monomers, or small repeating units within a greater whole, called a polymer.
These units may be identical, as with the glucose molecules arranged into long chains of the storage fuel glycogen, or they may be similar and come in "flavors," as with nucleic acids and the nucleotides that make them up.
The three major macronutrient classes of macromolecules in human nutrition, called carbohydrates, proteins and fats, each consist of their own type of monomer.
Glucose is the fundamental substrate of all of life on Earth, with every living cell capable of metabolizing it for energy. As noted, glucose molecules can be linked into "chains" to form glycogen, which in humans is found primarily in muscle and the liver. Proteins consist of monomers drawn from a grab-bag of 20 different amino acids.
Fats are not polymers because they consist of three fatty acids linked to a "backbone" of the three-carbon molecule glycerol. When they grow or shrink, this occurs via the addition or removal of atoms to the ends of the fatty acid chains, rather like a capital "E" with the vertical part remaining the same size but the horizontal bars varying in length.
What Is Anabolic Metabolism?
Consider being given a box of toy building blocks of unlimited size. Many are identical except in their color; others are different sizes, but can be joined together; still others are not meant to connect no matter the configuration you select. You can create identical constructs that include say, three to five pieces, and link these together in such a way that the junctions of these constructs are also identical.
This is essentially anabolic metabolism in action. The individual groups of three to five toy pieces represent "monomers" and the finished product is analogous to "polymer." And in cells, instead of your hands doing the work of putting the pieces together, enzymes guide the process. In both cases, the key aspect is an input of energy to generate molecules of greater complexity (and usually greater size as well).
Examples of anabolic processes include, in addition to protein synthesis, gluconeogenesis (the synthesis of glucose from various upstream substrates), the synthesis of fatty acids, lipogenesis (the synthesis of fats from fatty acids and glycerol) and the formation of urea and ketone bodies.
What Is Catabolic Metabolism?
Most of the time, catabolic processes, at the level of individual reactions, are not simply the corresponding anabolic reactions run in reverse, although many of them are the same. Usually, different enzymes are involved.
For example, the first step in glycolysis (the catabolism of glucose) is the addition of a phosphate group to glucose, courtesy of the enzyme hexokinase, to form glucose-6-phosphate. But the final step of gluconeogenesis, the removal of the phosphate from glucose-6-phosphate to form glucose, is catalyzed by glucose-6-phosphatase.
Other vital catabolic processes going on in your body are glycogenolysis (the breakdown of glycogen in muscle or liver), lipolysis (the removal of fatty acids from glycerol), beta-oxidation (the "burning" of fatty acids), and the degradation of ketones, proteins or individual amino acids.
Keeping a Balance of Anabolic and Catabolic Metabolism
Keeping the body in tune with its needs in real time requires a high degree of responsiveness and coordination. The rates of anabolic and catabolic reactions can be controlled by varying the amount of enzyme or substrate mobilized to a given part of the cell, or by feedback inhibition, in which the accumulation of a product signals the reaction upstream to proceed more slowly.
Also, and importantly from the standpoint of visualizing metabolism holistically, substrates from one macronutrient pathway can be shunted into that of another as needed.
An example of this integration of pathways is that the amino acids alanine and glutamine, in addition to serving as the building blocks of proteins, can also enter gluconeogenesis. For this to happen, they need to shed their nitrogen, which is handled by enzymes called transaminases.
- Glycerol, a product of lipolysis, can also enter the gluconeogenesis pathway, which is one way to, in a loose sense, get sugar from fat. To date, however, there is no evidence that products offatty acidoxidation can enter gluconeogenesis.
Physical Exercise:Muscle GrowthandFat Loss
Physical fitness is a major public concern in countries where people often have the luxury of optional exercise.
Many of the common modalities are aimed strongly in the direction of one process or another, such as lifting weights to build muscle mass (anabolic exercises) or using an elliptical trainer or treadmill for "cardio" and shedding lean or fatty body mass (or body weight) for weight loss (catabolic exercises).
One example of both systems in action is a marathon runner preparing for and running a 42.2-km (26.2-mile) race. The week before, many people intentionally load up on carbohydrate-rich foods while resting for the effort.
Because of their daily running training and the constant need to replace catabolized fuel, these athletes have high levels of activity of the enzyme glycogen synthase, which allows their muscles and liver to synthesize glycogen with unusual avidity.
During the marathon, this glycogen is converted to glucose to power the runner along for hours on end, though these athletes typically take in sources of glucose (e.g., sports drinks) throughout the event as well to prevent "hitting the wall."
- The inability of the body to generate glucose fromfatty acidsis the reason carbohydrates are considered critical forhigh-intensity, sustained exercise, as the beta-oxidation offatty acidsdoes not result in enoughATPto keep pace with metabolic needs.
Anabolic pathways build complex molecules from simpler ones and typically need an input of energy. Building glucose from carbon dioxide is one example. Other examples include the synthesis of proteins from amino acids, or of DNA strands from nucleic acid building blocks (nucleotides).What is an example of catabolic metabolism? ›
Some examples of the catabolic processes include glycolysis, the citric acid cycle, the breakdown of muscle protein in order to use the amino acids as substrates for gluconeogenesis, the breakdown of fat in adipose tissue to fatty acids, and oxidative deamination of neurotransmitters by monoamine oxidase.What is the difference between catabolic and anabolic metabolism in a cell? ›
Catabolism, at its core, involves breaking down of complex molecules and releasing energy for the body to use. The anabolic process is the complete opposite of catabolism as it involves creating bigger, complex molecules from smaller, simpler molecules. These are usually stored by the body for future use.What is a good example of catabolism? ›
Catabolism occurs when you're digesting food. For example, it's the process that dissolves a piece of bread into simple nutrients your body can use, like glucose (blood sugar).What are anabolic reactions give examples? ›
Examples of anabolism are bone growth mineralization and muscle mass build-up. Breakdown of proteins to amino acids, glycogen to glucose, and triglycerides to fatty acids are some of the catabolic processes.What is an example of an anabolic pathway in the cell? ›
One example of an anabolic pathway is the synthesis of sugar from CO2. Other examples include the synthesis of large proteins from amino acid building blocks and the synthesis of new DNA strands from nucleic acid building blocks.What is an example of a catabolic reaction in the body? ›
Glycolysis, food digestion, and beta-oxidation are some of the most well-known catabolic reactions.Is digestion an example of anabolism or catabolism? ›
The breakdown of food in digestion is a catabolic reaction (see digestive system).What are examples of catabolic hormones? ›
Adrenaline, cortisol, and glucagon are catabolic hormones. Glucose metabolism fluctuates with an individual's circadian rhythms which regulate anabolism and catabolism. Adrenaline, cortisol, and glucagon are catabolic hormones.What is an example of catabolic and anabolic reactions? ›
An example of an anabolic reaction is the synthesis of glycogen from glucose. An example of a catabolic reaction is the process of food digestion, where different enzymes break down food particles so they can be absorbed by the small intestine.
What is the difference between anabolic and catabolic pathways? catabolic reactions break down molecules and release energy by breaking down complex molecules to simpler compounds. Anabolic reactions build larger molecules from smaller ones, they consume energy to do this.Is glycolysis anabolic or catabolic? ›
Glycolysis is a universal catabolic pathway that converts glucose into pyruvate through a sequence of ten enzyme-catalyzed reactions, and generates the high-energy molecules ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).Is insulin anabolic or catabolic? ›
Insulin is considered to be an anabolic hormone in that it promotes the synthesis of protein and glycogen and it inhibits the degradation of these compounds in muscle tissue. Glucose normally provides energy sources for tissues of the body, its uptake by muscle requires a secretion of insulin.Is glucose an example of catabolism? ›
Breakdown of proteins to amino acids, glycogen to glucose, and triglycerides to fatty acids are some of the catabolic processes. Figurative representation of anabolic and catabolic processes.What is catabolism short answer? ›
Catabolism is defined as all chemical or enzymatic reactions involved in the breakdown of organic or inorganic materials such as proteins, sugars, fatty acids, etc. From: Bacterial Cellular Metabolic Systems, 2013.What is the difference between catabolic and anabolic reactions? ›
Anabolic reactions use energy to build complex molecules from simpler organic compounds (e.g., proteins from amino acids, carbohydrates from sugars, fats from fatty acids and glycerol); catabolic reactions break complex molecules down into simpler ones, releasing chemical energy.What are anabolic metabolic activities? ›
Metabolism is a balancing act involving two kinds of activities that go on at the same time: building up body tissues and energy stores (called anabolism) breaking down body tissues and energy stores to get more fuel for body functions (called catabolism)What is an example of a catabolic enzyme? ›
An example of a catabolic enzyme is DNA polymerase which catalyzes DNA synthesis. On the other hand, lipase is a catabolic enzyme that converts triglycerides into fatty acids and glycerol.Is respiration catabolic or anabolic? ›
Catabolism: Cellular respiration
Cellular respiration is a catabolic process during which glucose is broken down to release usable energy for a cell. As in all catabolic processes, cellular respiration releases energy which can then be harnessed and used by other reactions in the cell.
Since proteins are larger molecules put together from smaller ones, the process of protein synthesis is anabolic.
DNA replication is an anabolic process. Metabolism is the sum of all the chemical reactions in the body, which can be divided into two pathways, catabolism and anabolism.Is cortisol catabolic or anabolic? ›
As a catabolic hormone, cortisol increases availability of all fuel substrates for working muscles by mobilization of glucose, free fatty acids, and amino acids from endogenous stores (5).What is the most common catabolic reaction in the human body? ›
The most well-known examples of catabolic reactions include - glycolysis, digestion of food, and beta-oxidation. These reactions involve the breakdown of large organic molecules such as carbohydrates, proteins, and fats into smaller molecules.What are the three anabolic hormones? ›
Results: The key anabolic hormones are human growth hormone, insulin-like growth factor-1, insulin, and testosterone and its analogs. Although each has specific metabolic actions, there is also a very important hormone-hormone interaction.Is Dehydration an example of anabolism or catabolism? ›
Dehydration synthesis is an anabolic reaction.How do you remember anabolic or catabolic? ›
Catabolism involves all of the metabolic processes that tear down biomolecules, while anabolism is all of the metabolic processes that build biomolecules. One way to remember which is which is to think of 'catastrophe' for catabolism and 'steroids' for anabolism.What is an anabolic reaction simple definition? ›
Anabolic reactions involve the building of larger, complex molecules from smaller, simpler ones, and require an input of energy. Catabolic reactions are the opposite of anabolic reactions, and break the chemical bonds in larger, more complex molecules.Does catabolism release energy? ›
Catabolic reactions give out energy. They are exergonic. In a catabolic reaction large molecules are broken down into smaller ones.Is Glycogenesis anabolic or catabolic? ›
Glycogenesis, in contrast, is the process of anabolic synthesis of glycogen. Glucose molecules are phosphorylated to glucose-6-phosphate, converted to glucose-1-phosphate and UDP-glucose, and added to glycogen chains for storage.Is glucose to ATP catabolic or anabolic? ›
The breakdown of sugars illustrates how a single molecule of glucose can store enough energy to make a great deal of ATP, 36 to 38 molecules. This is a catabolic pathway. Catabolic pathways involve the degradation (or breakdown) of complex molecules into simpler ones.
Whereas, Calvin cycle is an anabolic pathway because it only involves the synthesis of glucose from carbon dioxide during photosynthesis.Is diabetes a catabolic? ›
Patients with insulin-dependent diabetes are in a catabolic state without insulin replacement. The mechanism of insulin's anticatabolic effect has been investigated in whole-body and regional tracer kinetic studies.What is the most anabolic hormone? ›
Insulin thus acts as an “anabolic” or storage hormone. In fact, many have called insulin “the most anabolic hormone”. Once insulin is in the blood, it shuttles glucose (carbohydrates), amino acids, and blood fats into the cells of the body.What is an anabolic hormone? ›
Endocrinologists have traditionally classified hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The classic anabolic hormones are the anabolic steroids, which stimulate protein synthesis and muscle growth, and insulin.
Glycolysis, which literally means “breakdown of sugar," is a catabolic process in which six-carbon sugars (hexoses) are oxidized and broken down into pyruvate molecules.Is carbohydrate a catabolism? ›
Carbohydrate catabolism is series of redox reactions that yield energy from carbohydrates. The energy is stored in the form high energy phosphate bonds of ATP, where it can be used quickly for various cellular processes.What is catabolism and its function? ›
Catabolism is the set of metabolic processes that break down large molecules. These include breaking down and oxidizing food molecules. The purpose of catabolic reactions is to provide the energy and components needed by anabolic reactions.What are the general functions of anabolism and catabolism? ›
Anabolic reactions are building reactions, and they consume energy. Catabolic reactions break materials down and release energy. Metabolism includes both anabolic and catabolic reactions. Every cell in your body makes use of a chemical compound, adenosine triphosphate (ATP), to store and release energy.What happens during anabolic metabolism? ›
Anabolism is the process by which the body utilizes the energy released by catabolism to synthesize complex molecules. These complex molecules are then utilized to form cellular structures that are formed from small and simple precursors that act as building blocks.What are the two main anabolic processes? ›
Growing in height and muscle mass are two basic anabolic processes. At the cellular level, anabolic processes can use small molecules called monomers to build polymers, resulting in often highly complex molecules.
Anabolic processes build organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules. Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass.Which is an anabolic type of metabolic reaction? ›
Anabolic reactions, or biosynthetic reactions, synthesize larger molecules from smaller constituent parts, using ATP as the energy source for these reactions. Anabolic reactions build bone, muscle mass, and new proteins, fats, and nucleic acids.Is digestion anabolic or catabolic? ›
The breakdown of food in digestion is a catabolic reaction (see digestive system). Foods are generally in the form of proteins, carbohydrates, and lipids (also called fats).What is anabolic and catabolic process? ›
Anabolism is the metabolic process that transforms simple substances into complex molecules. Catabolism is where complex and large molecules are broken down into small ones. Role in Metabolism.