Anabolic processes include the muscle contractions that provide animals with movement.
Metabolic processes are sequences of biochemical reactions that occur within living cells to maintain life. They can be divided into two main types. Catabolic processes, or pathways, involve breaking down complex food molecules into smaller units that can be used as building blocks for new molecules or to provide energy. Anabolic pathways involve using energy to build new chemicals that become components of cells. These reactions are made possible by a series of organic catalysts known as enzymes.
Catabolic processes are metabolic processes that break down food in the body to create new molecules or provide energy.
Together, the two types of metabolic processes allow for the transformation of raw materials, or nutrients, that are absorbed by an organism into tissue. A compound, common to all cellular life, is essential for these transformations. Adenosine triphosphate (ATP) is used to store energy obtained from nutrients such as carbohydrates and to release energy when needed to build new molecules.
DNA is built from nucleotides in a type of metabolic process known as anabolic.
Some organisms, like green plants, make their own food from inorganic materials, while others, like animals, consume organic materials for their nutrition. The food consumed by animals can be divided into three main types – carbohydrates, lipids (fats and oils) and proteins. Digestion involves catabolic processes that break them down into simpler components. For example, relatively complex carbohydrates such as polysaccharides and disaccharides are broken down into glucose and proteins into amino acids. These simpler compounds can be used by anabolic processes to build new materials, or they can be broken down to provide energy.
Anabaolic processes use food broken down by catabolic processes, but if it is broken down more than used, it can cause fat to accumulate in the body.
Cellular respiration is the process by which carbohydrate glucose (C 6 H 12 O 6 ) is broken down into carbon dioxide (CO 2 ) and water (H 2 O), producing energy that is stored in ATP. The procedure involves oxidation and, where atmospheric oxygen is available, it is used in what is known as aerobic respiration. This is the process that occurs in animals, plants and some microorganisms. The general reaction can be summarized as
C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O
but the process takes place in several stages and the details are quite complex.
Cells are powered by ATP, which is primarily synthesized by mitochondria.
Under conditions where there is no free oxygen, anaerobic respiration occurs. This is only found in certain microorganisms that live in soil, decaying organic matter, on the seafloor, underground and in the intestines of animals. These organisms use alternatives like nitrates, sulfates, fumarate and even sulfur in place of free oxygen. Anaerobic respiration is much less efficient than the aerobic process and produces much less ATP, but early in Earth’s history — before there was free oxygen in the atmosphere — this was the only form of respiration possible.
In animals, lipids are also oxidized to carbon dioxide and water, but the first steps are different. The chemistry of organisms takes place in a water-based environment, but fats and oils do not mix with water. The first step is to emulsify these substances, which means converting them into a form that mixes with water, in the same way that detergents can help clean up oil spills. This is done by soap-like substances contained in bile, released by the gallbladder into the small intestine. The lipids are then broken down into fatty acids and glycerol, which can be absorbed by the intestine and which can undergo oxidation reactions similar to those performed with carbohydrates.
Proteins are very large and complex molecules made of building blocks known as amino acids. They are metabolized by various reactions that break them down into their amino acids, which can then be absorbed and used within cells. Generally, proteins are not used to provide energy, but instead, amino acids are used to make new proteins to build tissue and muscle. In cases where no carbohydrates or fat are available in the diet, and the body has exhausted its fat stores, proteins can be used for energy by oxidizing their amino acids. In these cases, the body can start to break down muscle proteins.
Also known as biosynthesis, these are reactions that use up the energy stored in ATP by catabolic processes. They include the building of proteins from amino acids and the construction of DNA from nucleotides. In animals, the muscle contractions that power movement can also be included, as these require the use of stored energy. In plants, the synthesis of glucose from carbon dioxide and water through photosynthesis is another anabolic pathway.
Metabolic Processes and Body Weight
The energy obtained from food by catabolism may be used straight away, by anabolic processes, but if it is not used, much of it is stored as fat. The amount of energy that can be extracted from food can be measured in calories. Similarly, the amount used up by various forms of exercise can also be measured this way. If consistently more calories are consumed than are used, fat will build up, resulting in weight gain. Conversely, if more calories are used up than are consumed, the body will obtain energy by using its fat reserves, losing weight.