TLDR: Metabolism is the set of chemical reactions that happen in living organisms to sustain life. It involves converting food into energy, building blocks for cells, and getting rid of waste. These reactions are catalyzed by enzymes and allow organisms to grow, reproduce, and respond to their environment.

Metabolism is the process by which living organisms convert food into energy and other essential molecules. It involves a series of chemical reactions that take place in cells. These reactions serve three main functions: converting the energy in food into a form that can be used by cells, producing building blocks for proteins, lipids, nucleic acids, and carbohydrates, and eliminating waste products. Enzymes, which are specialized proteins, catalyze these reactions, allowing organisms to grow, reproduce, maintain their structures, and respond to their environment.

Metabolic reactions can be categorized as catabolic or anabolic. Catabolic reactions involve the breakdown of compounds, such as glucose, to release energy. Anabolic reactions, on the other hand, involve the synthesis of compounds, such as proteins, carbohydrates, lipids, and nucleic acids, which require energy. Enzymes play a crucial role in metabolism by facilitating these reactions and regulating their rate.

Metabolism is not only important for energy production and the synthesis of essential molecules, but it also determines which substances are nutritious or poisonous to an organism. Different organisms have different metabolic systems, which determine their nutritional needs and sensitivities to certain substances. For example, some bacteria can use hydrogen sulfide as a nutrient, while it is poisonous to animals. The basal metabolic rate is a measure of the amount of energy consumed by all the chemical reactions in an organism.

One fascinating aspect of metabolism is the similarity of the basic metabolic pathways among different species. For example, the set of chemical reactions known as the citric acid cycle is present in all known organisms, from bacteria to elephants. These similarities are likely due to the early appearance of these pathways in evolutionary history and their effectiveness in sustaining life.

Disruptions in normal metabolism can lead to various diseases, such as type II diabetes, metabolic syndrome, and cancer. The metabolism of cancer cells is different from that of normal cells, and these differences can be targeted for therapeutic intervention.

Metabolism involves the breakdown of macromolecules, such as proteins, carbohydrates, and lipids, into smaller units that can be used by cells. Digestive enzymes break down these macromolecules into their smaller components, which are then taken up by cells and converted into energy or used for building new molecules.

The energy from organic compounds, such as glucose, is extracted through a series of reactions called cellular respiration. This process involves the conversion of glucose into pyruvate and then into acetyl-CoA, which enters the citric acid cycle. The citric acid cycle generates ATP, the energy currency of cells, through a process called oxidative phosphorylation.

Inorganic compounds can also serve as a source of energy for some organisms. Chemolithotrophs, for example, obtain energy by oxidizing inorganic compounds, such as hydrogen, sulfur compounds, or ferrous iron. These organisms use specialized proteins in their cell membranes to pump protons, creating an electrochemical gradient that drives ATP synthesis.

Overall, metabolism is a complex and essential process that allows living organisms to obtain energy, build molecules, and maintain their structures. It is a fundamental aspect of life and plays a crucial role in the functioning of all living organisms.

Related Links:

• Cellular Respiration
• ATP