What is anabolism?
Anabolism is the phase of metabolism in which complex biochemical structures are generated from simpler substances. In other words, the chemical energy of the organism is invested to compose complex biomolecules from simple ones, using reducing power. It is an opposite and complementary process of catabolism.
The name of the term comes from the Greek ana (“up”) and ballein (“to launch”), since it implies the synthesis of more complex compounds from simpler ones, going “up” from the basic to the complicated. To be able to do this, however, an additional energy addition is required (endergonic reactions).
Like catabolism, it occurs inside cells and is driven by the action of enzymes ( catalyst proteins ).
Differences between anabolism and catabolism
Catabolism and anabolism are complementary, though opposite, processes. While catabolism breaks down macromolecules into simpler forms releasing the chemical energy contained in their chemical bonds, anabolism consumes that released energy to form new bonds and new complex molecules, going in the opposite direction.
Thus, one consumes energy, and the other releases it; one goes from the basic to the complex, and the other vice versa. When both catabolism and anabolism are in balance, the cell remains stable. But when it is necessary to grow or reproduce, anabolism predominates in them, to manufacture the additional biochemical pieces necessary to increase in size or complexity.
Importance of anabolism
Anabolism is a vital metabolic stage, not only to provide inputs to catabolism to break down and release chemical energy but also to:
- The storage of energy in the chemical bonds of complex molecules (such as starch from plants, or glycogen and triglycerides from animals).
- The elaboration of components of cells and tissues, thus allowing the increase of muscle mass and the growth of the organism.
- The manufacture of new cells to replace old ones and replenish damaged tissues.
In autotrophic beings (those capable of synthesizing on their own the necessary nutrients to sustain their existence), anabolism generally involves the transit of inorganic molecules (such as water, carbon dioxide, etc.) towards organic molecules of greater complexity and biochemical utility. This process can occur in two different ways:
- Photosynthesis. It is the metabolic process of plants and organisms endowed with chlorophyll, in which carbon dioxide (CO2) and water (H2O) are consumed to compose starch (sugar) molecules. This process gets its necessary energy from sunlight.
- Chemosynthesis. This process occurs mainly in microscopic organisms such as bacteria and archaea, in whose habitat there is no usable sunlight, but there is another type of chemical substance in constant reaction, which are used to synthesize organic molecules from, for example, ammonia (NH3 ).
In heterotrophic beings (which require consuming the organic matter of other living beings to feed themselves), anabolism differs from autotroph in that its simple compounds are organic, that is, they are the result of digestion and decomposition of food. The energy necessary for this is obtained from ATP (Adenosine Triphosphate) produced during catabolism.
Examples of anabolism
Anabolism can be exemplified in the growth phases of living beings: children that grow in weight and height, plants that put on new stems, animals that increase in size.
For an anabolic process to occur, new cells are required to make new tissue. This is achieved by increasing the amount of biochemical material and biochemical energy available to the body. In that case, plants require sunlight, carbon dioxide in the air and water, while animals and humans need food and oxygen.
Anabolic Vs Catabolism
- Anabolic metabolism has phases and divergence. The multi-level structure of biomolecules determines the stage of anabolism. First, small biological molecules (monosaccharides, amino acids, nucleotides, etc.) are synthesized from simple inorganic molecules (CO2, NH3, H2O, etc.), and then these building blocks are used to synthesize biological macromolecules, and then assembled into various biological structures. Divergence refers to the tendency to produce more types of products as the anabolism phase rises.
- Anabolic metabolism is nutritionally dependent. Humans cannot synthesize all biological molecules from scratch. Those substances that cannot be synthesized by themselves but can only be ingested from food are called essential nutrients. Such as essential amino acids, essential fatty acids, vitamins, etc. Strictly speaking, sugar is not essential.
- Anabolism requires energy to drive. Generally, when synthesizing small biological molecules, ATP is used to overcome energy barriers and NADPH is used for reduction. When synthesizing large biological molecules, ATP is used to activate the components. When the activated components are condensed, energy is no longer needed.
- The assembly of biological macromolecules requires a source of information, and there are two assembly modes. Macromolecules with complex building block sequences are assembled using templates, which require pre-existing information molecules as templates. For example, DNA replication, transcription, reverse transcription, and translation are all polymerization processes under the guidance of a template. The information of the primary structure comes from the component sequence of the template molecule, and the energy comes from the activated component molecule. The formation of high-level structures by biological macromolecules is a self-assembly process. The information exists in the primary structure, and its energy comes from non-covalent forces, that is, the free energy released during the assembly process.
- Macromolecules with simple and uniform building blocks are assembled and polymerized by the enzymatic assembly. The information instruction comes from the enzyme molecule and does not require a template. As glycogen, peptidoglycan, and some small peptides (such as glutathione, etc.) are synthesized under the guidance and catalysis of specific enzymes.
- Catabolism has phases and convergence. The decomposition of biological macromolecules has three stages: the hydrolysis of macromolecules produces component molecules, the oxidative decomposition of components produces metabolic intermediates such as acetyl-CoA, and finally oxidation to carbon dioxide and water. In this process, as the structural level decreases, there is a tendency to produce a few common decomposition products, that is, there is convergence.
- Each stage of catabolism is a process of releasing energy. In the first stage, there is very little energy and no ATP is produced. The second stage is about one-third of the energy released, which can synthesize a small amount of ATP and reduce coenzymes. The third stage releases the remaining energy through the tricarboxylic acid cycle and oxidative phosphorylation. The tricarboxylic acid cycle produces ATP and reduced coenzymes, which release energy during oxidative phosphorylation to form ATP and water.
- Catabolism and anabolism are often coupled with ATP. ATP can be decomposed into ADP or AMP when it provides energy. The former is the synthesis of various kinases, and the latter is the synthesis of acyl-CoA. In addition to ATP, other NTPs also have their roles. For example, UTP is involved in polysaccharide synthesis, CTP is involved in lipid synthesis, and GTP is involved in protein synthesis.
- In addition to the pyrophosphate bond of NTP, the enol phosphoric ester bond and thioester bond are also common high-energy bonds, and the energy released during hydrolysis is more than 20 kJ/mol. Therefore, phosphoenolpyruvate, acetyl-CoA, creatine phosphate, etc. are all high-energy compounds that can be used as energy carriers or energy stores.
- Creatine phosphate is a substance that temporarily stores energy in excitable tissues (such as muscles, brains, nerves, etc.), and is an energy storage reservoir for ATP. Creatine phosphate can transfer the phosphate group to ADP, thereby regenerating ATP, so it is called phosphate. Its content in muscle is 3-4 times higher than that of ATP and is used to maintain a constant ATP level.
- Metabolism is dynamic. Catabolism and anabolism are always going on in organisms at the same time, but the flow is constantly changing. Even if the bodyweight remains the same, metabolism is constantly progressing, decomposing aging biomolecules and synthesizing new molecules to replace them.
What is anabolism? and Anabolic Vs Catabolism