What Are Stem Cells?
Stem cells are unique cells of the body in that they are unspecialized and have the ability to develop into several different types of cells. They are different from specialized cells, such as heart or blood cells, in that they can replicate many times, for long periods of time. This ability is what is known as proliferation. Unlike other cells, stem cells also have the ability to differentiate or develop into specialized cells for specific organs or develop into tissues. In some tissues, such as muscle or brain tissue, stem cells can even regenerate to aid in the replacement of damaged cells.
Where Are Stem Cells Found?
Stem cells come from several sources in the body. The names of the cells below indicate the sources from which they are derived. Embryonic Stem Cells
These stem cells come from embryos in the early stages of development. They have the ability to differentiate into any type of cell in the initial stages of development and become slightly more specialized as they mature.
Fetal Stem Cells
These stem cells come from a fetus. At about nine weeks, a maturing embryo enters into the fetal stage of development. Fetal stem cells are found in fetal tissues, blood and bone marrow. They have the potential to develop into almost any type of cell.
Umbilical Cord Blood Stem Cells
These stem cells are derived from umbilical cord blood. Umbilical cord stem cells are similar to those found in mature or adult stem cells. They are specialized cells that develop into specific types of cells.
Placental Stem Cells
These stem cells are contained within the placenta. Like cord blood stem cells, these cells are specialized cells that develop into specific types of cells. Placentas however, contain several times more stem cells than do umbilical cords.
Adult Stem Cells
These stem cells are present in mature body tissues in infants, children and adults. They may also be found in fetal and umbilical cord blood cells. Adult stem cells are specific to a particular tissue or organ and produce the cells within that particular tissue or organ. These stem cells help to maintain and repair organs and tissues throughout a person's life.
Types of Stem Cells
Stem cells can be categorized into five types based on their ability to differentiate or their potency. The stem cell types are as follows: Totipotent Stem Cells
These stem cells have the ability to differentiate into any type of cell in the body. Totipotent stem cells develop during sexual reproduction when male and female gametes fuse during fertilization to form a zygote. The zygote is totipotent because its cells can become any type of cell and they have limitless replicative abilities. As the zygote continues to divide and mature, its cells develop into more specialized cells called pluripotent stem cells.
Pluripotent Stem Cells
These stem cells have the ability to differentiate into several different types of cells. Specialization in pluripotent stem cells is minimal and therefore they can develop into almost any type of cell. Embryonic stem cells and fetal stem cells are two types of pluripotent cells.
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- Induced pluripotent stem cells (iPS cells) are genetically altered adult stem cells that are induced or prompted in a laboratory to take on the characteristics of embryonic stem cells. Although iPS cells behave like and express some of the same genes that are expressed normally in embryonic stem cells, they are not exact duplicates of embryonic stem cells.
Multipotent Stem Cells
These stem cells have the ability to differentiate into a limited number of specialized cell types. Multipotent stem cells typically develop into any cell of a particular group or type. For example, bone marrow stem cells can produce any type of blood cell. However, bone marrow cells don't produce heart cells. Adult stem cells and umbilical cord stem cells are examples of multipotent cells.
- Mesenchymal stem cells are multipotent cells of bone marrow that have the ability to differentiate into several types of specialized cells related to, but not including blood cells. These stem cells give rise to cells that form specialized connective tissues, as well as cells that support the formation of blood.
Oligopotent Stem Cells
These stem cells have the ability to differentiate into just a few types of cells. A lymphoid stem cell is an example of a oligopotent stem cell. This type of stem cell can not develop into any type of blood cell as bone marrow stem cells can. They only give rise to blood cells of the lymphatic system, such as T cells.
Unipotent Stem Cells
These stem cells have unlimited reproductive capabilities, but can only differentiate into a single type of cell or tissue. Unipotent stem cells are derived from multipotent stem cells and formed in adult tissue. Skin cells are one of the most prolific examples of unipotent stem cells. These cells must readily undergo cell division to replace damaged cells.
Stopping Antibiotic Resistance
Scientists are taking a different approach to fighting antibiotic resistant bacteria. Instead of trying to kill the bacteria, they are looking to disarm them and make them incapable of causing infection. Monash University researchers have demonstrated that bacteria contain a protein complex called Translocation and Assembly Module (TAM). TAM is responsible for exporting disease causing molecules from the inside of the bacterial cell to the outer cell membrane surface. The researchers believe that this finding could spark the development of new drugs that would disrupt TAM functions.
According to researcher Joel Selkrig, "The TAM was discovered in many disease-causing bacteria, from micro-organisms that cause whooping cough and meningitis, to hospital-acquired bacteria that are developing resistance to current antibiotics. It is a good antibacterial target because a drug designed to inhibit TAM function would unlikely kill bacteria, but simply deprive them of their molecular weaponry, and in doing so, disable the disease process." The researchers also state that by keeping the bacteria alive, but harmless, it will prevent the development of antibiotic resistance.
Meiosis is a two part cell division process in organisms that sexually reproduce. Through a sequence of steps, the replicated genetic material in a parent cell is distributed among four daughter cells. Meiosis produces gametes with one half the number of chromosomes as the parent cell.
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There are two stages of meiosis: meiosis I and meiosis II. At the end of meiosis I, two daughter cells are produced, each with one half the number of chromosomes as the original parent cell. At the end of meiosis II, four daughter cells are produced, each with one half the number of chromosomes as the original parent cell. Meiosis is similar to another cell division process called mitosis. Mitosis produces two cells that are genetically identical to and contain the same number of chromosomes as the parent cell, while meiosis produces four cells that are not genetically identical to the parent cell and contain one half the number of chromosomes. This meiosis animation illustrates the meiotic process and compares it to the process of mitosis.
A research team from the University of Bonn has developed a new method for producing brain stem cells. The method allows for the direct production of induced neural stem cells that are capable of developing into various cells of the nervous system. The induced neural stem cells produced in the study were derived from the connective tissue cells of mice.
According to lead researcher, Dr. Frank Edenhofer, "Since we cut down on the reprogramming of the cells via the embryonic stage, our method is about two to three times faster than the method used to produce iPS cells." Induced pluripotent stem (iPS) cells are genetically altered adult stem cells that are induced or prompted in a laboratory to take on the characteristics of embryonic stem cells. These cells can develop into a variety of different types of cells and tissues. The researchers state that unlike cells derived from iPS cells or embryonic stem cells, there is a low risk of tumor formation. Because of this, the researchers envision that induced neural stem cells could be used to replace improperly functioning neurons and other cells of the nervous system.
Scientists have developed a novel method for detecting Salmonella bacteria in food products. The testing method can identify the presence of Salmonella in only five minutes. In the study, the researchers used gold nanoparticles with antibodies attached to them to identify Salmonella. Several nanoparticle-antibody structures attached themselves to Salmonella causing a color change to occur in the testing process. The experimental procedures were tested on a small sample of lettuce.
According to head researcher Paresh C. Ray, "It doesn't take a trained laboratory technician to perform the test or read the results. If the color changes from pink to bluish, that signals the presence of Salmonella. The test is suitable for use in farm fields and in remote areas of the developing world. We believe it may have enormous potential for rapid, on-site pathogen detection to avoid the distribution of contaminated foods." The researchers also state that the process can potentially be used to destroy bacteria as well. When Salmonella contaminated water was exposed to the appropriate wavelength of light, the gold nanoparticles heated up causing damage to the cell membrane of the bacteria.
