Which cells continually divide

The various checks on cell growth that occur during interphase allow tissues to revitalize themselves without increasing in size. When these restraints fail, the results — including the growth and spread of cancer — can be devastating.

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Change LearnCast Settings. That means we lose around 50 million cells every day. This is a lot of skin cells to replace, making cell division in skin cells is so important. Other cells, like nerve and brain cells, divide much less often. Depending on the type of cell, there are two ways cells divide—mitosis and meiosis. Each of these methods of cell division has special characteristics. One of the key differences in mitosis is a single cell divides into two cells that are replicas of each other and have the same number of chromosomes.

This type of cell division is good for basic growth, repair, and maintenance. In meiosis a cell divides into four cells that have half the number of chromosomes.

Reducing the number of chromosomes by half is important for sexual reproduction and provides for genetic diversity. Mitosis is how somatic — or non-reproductive cells — divide. Somatic cells make up most of your body's tissues and organs, including skin, muscles, lungs, gut, and hair cells.

Reproductive cells like eggs are not somatic cells. In mitosis, the important thing to remember is that the daughter cells each have the same chromosomes and DNA as the parent cell. The daughter cells from mitosis are called diploid cells. Diploid cells have two complete sets of chromosomes.

Since the daughter cells have exact copies of their parent cell's DNA, no genetic diversity is created through mitosis in normal healthy cells.

Mitosis cell division creates two genetically identical daughter diploid cells. The major steps of mitosis are shown here. Before a cell starts dividing, it is in the "Interphase. Interphase is the period when a cell is getting ready to divide and start the cell cycle. During this time, cells are gathering nutrients and energy. The parent cell is also making a copy of its DNA to share equally between the two daughter cells. The mitosis division process has several steps or phases of the cell cycle—interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis—to successfully make the new diploid cells.

The mitosis cell cycle includes several phases that result in two new diploid daughter cells. Each phase is highlighted here and shown by light microscopy with fluorescence. Click on the image to learn more about each phase. When a cell divides during mitosis, some organelles are divided between the two daughter cells.

For example, mitochondria are capable of growing and dividing during the interphase, so the daughter cells each have enough mitochondria. The Golgi apparatus, however, breaks down before mitosis and reassembles in each of the new daughter cells. Many of the specifics about what happens to organelles before, during and after cell division are currently being researched. You can read more about cell parts and organelles by clicking here.

Meiosis is the other main way cells divide. Meiosis is cell division that creates sex cells, like female egg cells or male sperm cells. What is important to remember about meiosis? In meiosis, each new cell contains a unique set of genetic information. After meiosis, the sperm and egg cells can join to create a new organism. Meiosis is why we have genetic diversity in all sexually reproducing organisms. During meiosis, a small portion of each chromosome breaks off and reattaches to another chromosome.

This process is called "crossing over" or "genetic recombination. The end result of meiosis is four haploid daughter cells that each contain different genetic information from each other and the parent cell. Click for more detail. The result is that the genes responsible for cell division are turned on and the cell divides.

For example, a cut in the skin leads certain blood cells, platelets, to produce a growth factor that causes the skin cells to reproduce and fill the wound. Cell division is a normal process that allows the replacement of dead cells.

Contact inhibition Cells are also able to sense their surroundings and respond to changes. For instance, if a cell senses that it is surrounded on all sides by other cells, it will stop dividing. In this way, cells will grow when needed but stop when their goal has been met.

To revisit our wound example, the cells fill in the gap left by the wound but then they stop dividing when the gap has been sealed. Cancer cells do not exhibit contact inhibition. They grow even when they are surrounded by other cells causing a mass to form. The behavior of normal top animation and cancer cells bottom animation with regard to contact inhibition is depicted below.

The round containers in which the cells are depicted in the animations are called petri dishes. In the laboratory, cells are often grown in these, covered with a nutrient-rich liquid.

Cellular Senescence Most cells also seem to have a pre-programmed limit to the number of times that they can divide. Interestingly, the limit seems to be based, in part, on the cell's ability to maintain the integrity of its DNA. An enzyme , telomerase , is responsible for upkeep of the ends of the chromosomes.

In adults, most of our cells don't utilize telomerase so they eventually die. In cancer cells, telomerase is often active and allows the cells to continue to divide indefinitely. For more information on telomerase, see the Cancer Genes section. Continued cell division leads to the formation of tumors. The genetic instability that results from aberrant division contributes to the drug resistance seen in many cancers. Mutations in specific genes can alter the behavior of cells in a manner that leads to increased tumor growth or development.

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