Metabolic Process: What It Is and Why It Matters
Metabolism is the sum of the chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material. Metabolism is essential for life, as it allows cells to extract energy from their environments, use it to carry out activities such as movement, growth and development, and reproduction, and synthesize the molecules required for growth and maintenance.
In this article, we will explore what metabolic processes are, how they are categorized, and what are some examples of important metabolic pathways in living organisms.
What are metabolic processes?
A metabolic process is a series of connected chemical reactions that feed one another. The pathway takes in one or more starting molecules and, through a series of intermediates, converts them into products. Metabolic processes can be broadly divided into two categories based on their effects:
- Anabolic processes are those that build larger molecules from smaller ones, such as the synthesis of proteins from amino acids. Anabolic processes usually require energy input, as they create new bonds and reduce entropy.
- Catabolic processes are those that break down larger molecules into smaller ones, such as the breakdown of glucose into carbon dioxide and water. Catabolic processes usually release energy, as they break bonds and increase entropy.
The energy released by catabolic processes can be captured and stored by the cell in the form of adenosine triphosphate (ATP), which is the universal energy currency of life. ATP can then be used to power anabolic processes and other cellular functions.
Examples of metabolic processes
There are thousands of metabolic processes that take place inside a cell, but some of them are more fundamental and widespread than others. Here are some examples of important metabolic pathways in living organisms:
- Photosynthesis is the process by which plants, algae, and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen. Photosynthesis is an anabolic process that produces organic molecules that can be used as food by the organism or other consumers. Photosynthesis also generates oxygen, which is essential for aerobic respiration.
- Cellular respiration is the process by which most cells, including animal cells, obtain energy from glucose by breaking it down into carbon dioxide and water. Cellular respiration is a catabolic process that releases energy, which is captured by the cell in the form of ATP. Cellular respiration can be aerobic (using oxygen) or anaerobic (without oxygen). Aerobic respiration is more efficient and produces more ATP per glucose molecule than anaerobic respiration.
- Glycolysis is the first stage of cellular respiration, in which glucose is split into two molecules of pyruvate. Glycolysis is a catabolic process that occurs in the cytoplasm of all cells and does not require oxygen. Glycolysis produces a net gain of two ATP molecules and two molecules of nicotinamide adenine dinucleotide (NADH), which is another energy carrier. NADH can be used to generate more ATP in the later stages of cellular respiration or recycled back to NAD+ in fermentation.
- Citric acid cycle (also known as Krebs cycle or tricarboxylic acid cycle) is the second stage of aerobic cellular respiration, in which pyruvate is oxidized into carbon dioxide and water. The citric acid cycle is a catabolic process that occurs in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotic cells. The citric acid cycle produces two ATP molecules and several molecules of NADH and flavin adenine dinucleotide (FADH2), which are also energy carriers. NADH and FADH2 can be used to generate more ATP in the final stage of cellular respiration: oxidative phosphorylation.
- Oxidative phosphorylation