A somatic cell is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, or undifferentiated stem cell. The word “somatic” originates from the Greek word “soma,” meaning body, highlighting their role as foundational components of an organism’s physical structure. In humans, somatic cells are diploid, meaning they contain two complete sets of chromosomes, with one set inherited from each parent, for a total of 46. These cells comprise the vast majority of the body, including all internal organs, skin, bones, blood, and connective tissue.
Somatic Cells vs. Other Cell Types
Somatic cells are distinct from germ cells, which are the reproductive cells—sperm in males and eggs in females. The primary difference is their chromosome number; while somatic cells are diploid, germ cells are haploid, possessing only a single set of 23 chromosomes. This distinction ensures that when a sperm and egg fuse during fertilization, the resulting zygote is diploid with the correct total of 46 chromosomes.
Another type of cell distinct from somatic cells is the stem cell. Stem cells are undifferentiated, meaning they have not yet developed into a specialized cell type, which allows them to transform into various kinds of cells. In contrast, somatic cells are terminally differentiated. A liver cell, for example, has a specific function and cannot transform into a lung cell because its developmental fate is determined.
The genetic information in somatic cells governs the individual’s body but is not passed to subsequent generations. Any changes or mutations in a skin cell will only affect that individual. Conversely, the genetic material within germ cells is the blueprint transmitted to offspring, carrying hereditary traits from one generation to the next.
The Role of Somatic Cells in the Body
Somatic cells are the building blocks of the body, organizing themselves into tissues, which are groups of cells with a common function. For instance, cardiac muscle cells group together to form cardiac tissue, which enables the heart to pump blood. These tissues, in turn, assemble to form organs like the heart and lungs, which create complex systems that keep the organism alive.
The body grows, heals, and maintains itself through a process of cell division called mitosis. During mitosis, a single somatic cell divides into two identical daughter cells, each with the same genetic information as the parent. This process allows a fertilized egg to develop into a full-grown organism. It also enables the replacement of old or damaged cells like skin cells and facilitates wound healing.
Different types of somatic cells are highly specialized to perform specific tasks. Nerve cells, or neurons, have long extensions that allow them to transmit electrical and chemical signals throughout the body. Muscle cells are filled with contractile proteins that enable movement. This specialization, or differentiation, occurs during embryonic development, where stem cells receive cues that direct them to become one of many distinct cell types.
Somatic Cells and Genetic Changes
The DNA within somatic cells can undergo changes, known as somatic mutations. These mutations occur after conception and can arise from errors during DNA replication or exposure to environmental mutagens. Because these changes happen in body cells, they affect only the individual and are not passed on to their children. Many somatic mutations are harmless.
Certain somatic mutations, however, can have serious consequences. Cancer is a primary example, driven by the accumulation of mutations in genes that regulate cell growth and division. When these genes are damaged, cells can begin to divide uncontrollably, forming tumors. This uncontrolled division is essentially mitosis gone awry.
Genetic changes in somatic cells also play a part in the aging process. One mechanism is cellular senescence, a state where cells lose their ability to divide. After a certain number of mitotic divisions, a cell’s telomeres—protective caps at the ends of chromosomes—shorten to a point where the cell stops replicating. This process contributes to aging as the body’s ability to repair tissues diminishes.
Somatic Cells in Scientific Applications
Scientists utilize somatic cells for various research and therapeutic purposes, such as Somatic Cell Nuclear Transfer (SCNT). This is the laboratory process used for creating a cloned organism. It involves removing the nucleus from an organism’s somatic cell. This nucleus is then transferred into an egg cell from which the original nucleus has been removed.
The reconstructed egg cell, now containing the diploid set of chromosomes from the donor, is stimulated to begin dividing. If the resulting embryo is implanted into a surrogate mother, it can develop into a genetic copy of the individual that provided the somatic cell. This was the technique used to create Dolly the sheep, the first mammal cloned from an adult somatic cell in 1996.
Beyond reproductive cloning, SCNT is also explored for therapeutic purposes. The process can be used to create patient-specific stem cells by allowing the cloned embryo to develop for a few days and then harvesting its embryonic stem cells. These cells are genetically matched to the patient, which could be used to grow new tissues or organs for transplantation without the risk of immune rejection.