Anabolism Definition

Anabolism collectively refers to all the processes of chemical reactions that build larger molecules out of smaller molecules or atoms; these processes are also known as anabolic processes or anabolic pathways. The opposite of anabolism is catabolism, the set of processes that breaks down larger molecules into smaller ones. 

Anabolism and catabolism are the two types of metabolic pathways. Metabolic pathways are series of chemical reactions that take place in the cell. Anabolic pathways use energy, while catabolic pathways release energy.

Function of Anabolism

Anabolic pathways in a cell lead to the formation of larger, more complex molecules from smaller ones. First, catabolic pathways are needed to break down nutrient molecules from food into small building blocks. These smaller molecules are then joined together to make different, bigger molecules called macromolecules. 

Anabolic pathways involve the input of energy, which is needed to form chemical bonds between smaller molecules to make macromolecules. Molecules built from anabolism are then used to build structures in the cell, or even to help build new cells. Anabolism and catabolism are controlled by circadian rhythms, and both are important for the development, growth, and maintenance of an organism’s cells.

Anabolic hormones are chemicals that cause cellular growth through activating anabolic pathways. Two examples of anabolic hormones are testosterone and insulin. Hormones can also be produced artificially in the lab; this is how anabolic steroids are created.

Examples of Anabolic Processes

Protein Synthesis

Proteins are macromolecules that carry out cellular activities encoded by an organism’s genes. They have many different functions in the body, including DNA replication, aiding chemical reactions (as enzymes), transporting materials in the cell, cell growth and signaling, and providing physical structure. Each cell in the human body contains about 1 to 3 billion proteins.

Proteins are synthesized from smaller molecules called amino acids in a cell’s ribosomes. Each protein is a chain of a specific sequence of amino acids. Since proteins are larger molecules put together from smaller ones, the process of protein synthesis is anabolic.

DNA Synthesis

Deoxyribonucleic acid, or DNA, is an organism’s genetic material. It is macromolecule made up of smaller molecules called nucleic acids, which are themselves made up of a nucleotide base attached to a deoxyribose sugar and a phosphate molecule. DNA synthesis is an anabolic process that takes place in a cell’s nucleus just before the cell divides. 

It involves unzipping the double strands of DNA and attaching new matching nucleotides to each half of the strand that has been unzipped, forming two new strands that each contain half of the old DNA strand.

Growth of Bones and Muscles

On a larger scale, the growth of body parts such as bones and muscles is anabolic. Bone growth, or ossification, occurs when bone is formed from cells called osteoclasts. It is then mineralized through cells called osteoblasts. 

This process is also anabolic; during mineralization, osteoblasts produce calcium phosphate crystals that are incorporated into the bone’s structure, making the bones hard and sturdy.

Muscle growth, also called muscle hypertrophy, occurs when the cells of skeletal muscles, called myocytes, increase in size. It occurs through strength training exercises such as lifting weights. Factors like sex, age, and diet all affect hypertrophy. During hypertrophy, there is increased protein synthesis of actin and myosin, and the volume of sarcoplasmic fluid in the myocyte increases.

Anabolic Steroids

Anabolic steroids are androgenic hormones that are natural (e.g. testosterone) or produced synthetically and mimic the effects of testosterone. Androgens are anabolic; they increase protein within muscle cells, which causes an increase in muscle mass. 

Anabolic steroids are used to treat certain medical conditions like delayed puberty in boys, and they can also be used for muscle growth, to stimulate the appetite, to produce secondary sex characteristics in transgender males, and to help treat certain conditions that may cause a loss in muscle mass, such as cancer and AIDS.

However, sometimes anabolic steroids are also abused by athletes who want to quickly gain more muscle. Most major sports organizations ban doping, the use of anabolic steroids or other performance-enhancing drugs, in order to discourage steroid abuse. Although using steroids can increase muscle mass, it also has many adverse side effects. 

These range from acne to high blood pressure to aggression (“’roid rage”), and even psychosis. Steroids can affect the structure of the heart, which could lead to congestive heart failure or a heart attack. They also have adverse effects on cholesterol levels, may stunt height, and can lead to liver damage in high doses.

In females, steroids can cause masculinization, which is the development of male secondary sex characteristics such as a deeper voice, increases in body hair, an enlarged clitoris (the clitoris in females is homologous to the penis in males), and temporary disruption of the menstrual cycle. 

In males, however, steroids can cause feminization, including the development of breast tissue and decrease in testicle size. This occurs because testosterone can be converted to estradiol, a female sex hormone. The effects of masculinization and feminization are generally reduced/reversed when a person stops taking steroids and their hormone levels return to normal.

Related Biology Terms

  • Catabolism – The set of processes that breaks down large molecules into smaller ones.
  • Metabolic pathway – A series of chemical reactions in the cell.
  • Macromolecule – A very large and complex molecule.
  • Anabolic steroids – Hormones used to treat conditions in which an increase in muscle mass is needed; they are also sometimes abused by athletes.

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