The human body has billions of cells. These are small building blocks responsible for maintaining and building tissues and organs. In order for cells to maintain, divide or destroy themselves, a cell cycle takes place. The cell cycle in the organism consists of cell growth and division. Cell growth concerns the increase in size and volume of all individual cells. It is genetically controlled and takes place before and between cell division. The prerequisite is cellular metabolism, also called metabolism, whereby cells process nutrient molecules.
What is cell growth?
In order for cells to maintain, divide or destroy themselves, a cell cycle takes place. The cell cycle in an organism consists of cell growth and division. In a living organism, cells are constantly dying. In humans, there are several hundred million cells whose loss necessitates the formation of a new cell. If a new cell is formed, cell division takes place. Signaling cascades, messenger substances and hormones are necessary for this, which also cause cell growth. When a single cell grows, the process is extremely complex. When a bacterial cell grows, for example, about two thousand chemical reactions take place at once. These include energy release processes, biosynthesis of small molecules to bind macromolecules, or polymerization reactions. In the process, all cellular structures are formed during cell growth, including cell walls, ribosomes or flagella.
Function and task
During cell growth, each additional cell receives a complete chromosome and, as a result, enough information about all monomers, ions, and macromolecules for another independent cell to exist. Multicellular organisms, in turn, grow by multiplying these self-formed cells. For reproduction, cells need stimuli. These can be growth hormones, for example. Until the first division of a cell begins, cell growth always takes place. The time cycle of cell growth depends on genetic factors and on the environment. The functions of cells and activity of genes are controlled by genetic circuits and also influence the growth effects. Different rates of cell growth can, for example, cause certain processes to occur more slowly in microorganisms. At the same time, natural selection also takes place, favoring cells that grow faster than others. Cell growth is also further differentiated into the cycle that takes place in the organism and the creation of cell cultures. Whereas bacteria, for example, can divide again after only twenty minutes, the period for a human cell and its division is a little more than ten hours. The growth of a cell is calculated in the ratio of surface area to volume. Due to this ratio, the cell soon does not have enough surface area to remove enough pollutants and absorb enough nutrients. Therefore, its growth is limited, both in unicellular organisms and in the development of multicellular organisms. Cell growth takes place conditionally in the body, but is also carried out as cell culture. In this respect, cells are multiplied and reused at a certain stage, e.g. for various experiments to study diseases. A single cell has an individual cell age, which starts after mitosis and reaches a maximum value at the next division, which corresponds to the doubling time. The division of one cell into two, of two cells into four, and so on, is called exponential or unlimited growth. Certain nutrients and minerals are important for cell growth, including potassium. This regulates cell growth, which in turn maintains the balance of acids and bases in the body, as well as the release of hormones. Basically, cells produce proteins that regulate cell growth and also have an impact on genes. Thus, cell growth also determines the better evaluation of genes. Changes in a cell affect the concentration of proteins produced. In rapidly growing cells, more polymerases are present, which enable transcription of genes. Nevertheless, the fact that the activity of genes depends on cell growth makes it difficult to measure genetic circuits. The metrics that characterize an activity of genes depend on protein concentration and growth rate. The growth rate is the increase of a size in a certain period of time. It is calculated by the growth factor.
Diseases and ailments
Cell growth is of particular interest in oncology, whose research focuses on the growth of cancer cells. Here, cell number also plays an important role in addition to cell growth. If the genetic material of a cell is disturbed, it can change pathologically. If the number of such cells is low, the body’s own defense system reacts with destruction or renewal. Only when cells of this type grow uncontrollably and divide do benign or malignant growths form, which are known as tumors. In the case of a malignant tumor, the tissue boundary is soon exceeded by growth. In this process, the surrounding tissue is destroyed and new growths are formed. Cancer cells behave like normal cells in this process. They do not know when to stop dividing or die. Similarly, they do not adhere firmly to each other, so they can separate from their cell association and migrate. In this way, they can subsequently continue to grow elsewhere. This is then called metastasis. In turn, when the tumor cells continue to grow, they soon form their own blood vessels to receive oxygen, hormones and glucose. This then allows the tumor to invade surrounding tissue.
