The first step in cell growth is the transference of nutrient molecules into the cell through its plasma membrane. Once inside, these molecules are broken down into less complex components that are used for energy and the production of new organelles. Each organelle, or "little organ," carries out its own function that aids in cell growth and survival. While different types of cells may contain different organelles, examples that are found in every type include centrioles, ribosomes and mitochondria.
The process by which a cell reproduces is called cell division. The two types are mitosis and meiosis. Mitosis, the more common process, occurs in somatic cells, which contain two sets of 23 chromosomes. Mitosis involves this one cell's replicating itself, resulting in two "daughter" cells that are identical to the original "parent." Meiosis applies only to gametes (eggs and sperm). Gametes differ from somatic cells in that they contain only one set of 23 chromosomes. Meiosis involves combining the two gametes into one cell that contains twice as many chromosomes, or two sets of 23.
Protein synthesis is the creation of new proteins within the cell and occurs in two steps: transcription and translation. Transcription is the preparatory process in which information from the cell's DNA, located in the nucleus, is used to create an extra strand of RNA (mRNA). This strand serves as a messenger carrying information found in DNA to other parts of the cell. Translation is the process that occurs once the mRNA connects to a ribosome and is then converted into a new protein molecule.
Every cell is enclosed in a selectively permeable membrane. By carefully regulating what may enter and exit through this membrane, the cell is able to maintain equilibrium, or a stable internal environment. Two common activities that accomplish this are endocytosis and exocytosis. While endocytosis deals with moving molecules into the cell, exocytosis refers to transporting materials out.