Living organisms are unique in that they can extract energy from their environments and use it to carry out activities such as movement, growth and development, and reproduction. At the cellular level of organization, the main chemical processes of all living matter are similar, if not identical. This is true for animals, plants, fungi, or bacteria; where variations occur (such as, for example, in the secretion of antibodies by some molds), the variant processes are but variations on common themes. The Greek word metaballein is the origin of the word metabolism meaning "to change." Its origin supports the idea that the nutrients received and used in metabolism change and renew the contents of the cell. 

Metabolism is the total amount of the biochemical reactions involved in maintaining the living condition of the cells in an organism. All living organisms require energy for different essential processes and for producing new organic substances. The metabolic processes help in growth and reproduction and help in maintaining the structures of living organisms. The organisms respond to the surrounding environment due to metabolic activities. All the chemical reactions occurring in the living organisms from digestion to transportation of substances from cell to cell require energy. This energy gets used for vital processes and the synthesis of new organic material. Every living organism uses its environment to survive by taking nutrients and substances that act as building blocks for movement, growth, development, and reproduction. The first stage of metabolism is to convert food into available energy. The second stage is to use the available energy to build essential molecules. The third stage is to eliminate metabolic waste.

Basal metabolic rate (BMR) refers to the minimum number of calories your body needs to function while you’re resting. This amount varies from person to person. BMR fulfills 60% to 70% of the energy your body uses. Rapid weight loss and aggressive calorie restriction decrease BMR — this is one reason why weight loss is usually not linear and may stall at some point.

Someone with a fast metabolism or fast BMR burns a lot of calories even while at rest. If you have a slow metabolism or slow BMR, your body needs fewer calories to keep it going. A fast metabolism does not necessarily lead to thinness. In fact, studies show that people with overweight/obesity often have fast metabolisms. Their bodies need more energy to keep basic body functions going.

Anabolism is the constructive metabolism accompanying synthesis and production of complex molecules from simpler monomers of biochemicals. If catabolism releases energy through the breaking of bonds, then anabolism stores energy through the formation of bonds. An example of an anabolic reaction would be glycogenesis, the process of building glycogen from individual glucose molecules. Glycogen is a glucose storage molecule that releases sugar when blood glucose levels are low. Recall that in catabolism, water is used to break substances down. In anabolism, water is removed to bind substances together. This is called dehydration synthesis.

Catabolism is the destructive metabolism accompanying the breakdown and degradation of complex molecules to simpler monomers of biochemicals. Organic molecules store energy within their bonds. When those bonds are broken through catabolic reactions, energy is released. Recall that a major function of metabolism is to convert food into available energy for the cell. A series of catabolic reactions are responsible for this conversion through hydrolysis, the breakdown of substances in the presence of water. Glycolysis is an example of a catabolic biological pathway. Glycolysis is the breakdown of sugar into pyruvate (an intermediate of cellular respiration) for the overarching purpose of creating energy. In glycolysis, one glucose molecule yields two smaller pyruvate molecules.

When we refer to biologically-active molecules, we are actually referring to chemical molecules that have biological activity and play a pivotal role in sustaining essential biological pathways. There are majorly 4 basic biochemicals: carbohydrates, lipids, nucleic acids, and proteins. Apart from these four are two more biochemicals that are generally studied. They are coenzymes and minerals. All these molecules play some of the most vital roles without which the proper functioning, coordination, and efficiency of biological systems.

The pancreas is the key metabolic organ that regulates the number of carbohydrates in the blood, either by releasing significant amounts of insulin to downregulate the levels of blood glucose or releasing glucagon to upregulate them. The utilization of carbohydrates and lipids by the organism is called the Randle cycle, regulated by insulin. The liver is the organ in charge of processing the absorbed amino acids and lipids from the small intestine. It also regulates the urea cycle and essential metabolic processes like gluconeogenesis and glycogen deposition.

Amino acids and proteins are the basic structural unit of all cells. Proteins are the building blocks of any biological entity. Proteins are actually polymers that are made up of monomers called amino acids. Amino acids are organic compounds having 2 essential groups: amino group and carboxylate groups. Then there’s one side chain group that is specific to each amino acid. Different or same amino acids are linked to each other via peptide bonds and form long peptides (polypeptides/ proteins). Amino acids are of 2 types: essential and non-essential in humans. Non-essential ones can be synthesized by the human body but essential ones need to be taken via diet. There is no such concept of essential and non-essential amino acids for plants since they can produce all of them. Protein synthesis from amino acids encompasses 4 major steps: transcription, translation of proteins, PTMs (post-translational modifications), and protein folding. The breakdown of proteins is specifically called proteolysis. After the proteins are broken down to the monomeric form i.e. amino acids, they are further reduced by degradations to individual atoms like nitrogen, oxygen, carbon, and hydrogen (also sulfur, selenium in some specific amino acids).

Metabolism is dependent upon nutrient consumption. When nutrients are consumed, the body breaks down large molecules to provide available energy to cells. This energy, along with any necessary building blocks, is used to make essential molecules such as new proteins and nucleic acids like deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nutrients are consumed as carbohydrates, proteins, fats, vitamins, and minerals.

Many people blame metabolic problems for weight struggles. But metabolism naturally regulates itself to meet body’s needs. It’s rarely the cause of weight gain or loss. In general, anyone who burns more calories than they take in will lose weight.

The amount of energy expended as a result of physical activity is the only component of metabolism that is entirely within an individual's control. Physical scientists recommend that a person receives at least 30 minutes of moderate exercise per day. Moderate exercise is defined as an intensity level that allows an individual to talk but not sing while exercising.

Many factors can affect how metabolism functions, these include: Muscle mass: It takes more energy (calories) to build and maintain muscle than fat. People with more muscle mass often have faster metabolisms that burn more calories. Age: You lose muscle as you get older, which slows down the metabolism. Males tend to have faster metabolisms than females. They have more muscle mass, larger bones and less body fat. Genes: The genes you inherit from your parents play a role in your muscle size and ability to build muscle mass. Physical activity: Walking, chasing after your kids, playing tennis and other forms of exercise cause your body to burn more calories than being sedentary. Smoking: Nicotine speeds up your metabolism, so you burn more calories. This is one reason people who quit smoking may put on weight. But the health consequences of smoking are: cancer, high blood pressure, coronary artery disease.

Published : Dec 12 2023