Course: SAT 170 Introductory Biotechnology

Unit 8 Learning Module

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Cell Cloning (continued)

Figure 5 | Figure 4 | More recently, plant tissue cultures are used to produce clones of plant tissues, organs or entire plants using a technique known as micropropagation. Such cultures take advantage of the fact that plant cells are often totipotent, which means that they are able to differentiate into any cell type within the plant. Very early in the developmental processes of multicellular organisms, the cells of that organism undergo a process of differentiation, where they acquire a specialized form and function. For example, in a plant embryo there will be cells that will develop into the leaf of the plant and others that will develop into the roots. In plants many cells that are already differentiated, such as leaf cells, can go through a process known as dedifferentiation. These dedifferentiated cells can then be used to generate an entire plant with many different specialized or differentiated cell types. Such plant tissue cultures need a special type of media which contains the appropriate nutrients and plant hormones to stimulate development of the plant. Plant cultures are incredibly important for screening and growing plants with certain desirable characteristics. These culture methods can also be used to grow plants of endangered species. Figure 4: Notice how the plant cultures used for micropropagation rely on a growth medium (shown as an opaque gel-like substance at the bottom of the flask) in the growth container rather than a typical soil substrate. This media contains all of the essential nutrients and plant hormones necessary for the growth of the culture. Figure 5: Here are several samples of Barley hybrids grown via the method known as micropropagation. |
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There are a variety of different animal cell cultures, including cultures of human cells as well as insect cells. The first step to creating an animal cell culture is to collect a sample of cells from an individual. These cells, referred to as primary cells are used to establish a primary cell culture. These cells are placed on media containing a complex of nutrients and hormones specific to the needs of the organism from which the cells were taken. These cultures must also be placed in incubators that have the appropriate environmental conditions including the optimal temperature of the organism from which the cells were collected. Once the cells have been successfully cultured they can be used to develop a cell line. A cell line represents a series of cultures that are prepared from that original culture by taking cells from the primary culture and placing them in new media. This is necessary as animal cells tend to undergo a process known as senescence when grown in culture.  Senescence occurs when the cells stop dividing to produce new cells eventually leading to cell death. Senescence is thought to be, at least in part, influenced by telomeres. Recall from unit 3 that a telomere is a sequence of nucleotides located on the ends of linear chromosomes. You may also recall from unit 3 that during the process of DNA replication, which occurs every time a cell divides to produce new cells, the strand of DNA is shortened. Once this shortening surpasses the length of the telomere, the genetic material will be compromised leading to reduced viability of those cells. By transferring the cells periodically to new media, the cells will receive the necessary nutrients and are more likely to remain viable. However, cell cultures that are made of cells that produce telomerase (which as you may recall from unit 3 is the enzyme that is used to extend the telomere after DNA replication) have a better chance of long-term survival. Examples of cells that exhibit high levels of telomerase activity are cancer cells and stem cells. In fact, the oldest human cell line, known as HeLa cells are cervical cancer cells that were first collected from a woman known as Henrietta Lacks in 1951. Such cell lines are important for the growth of transplant tissues and organs as well as for studying the effects of certain drugs and toxins on human cells. We will explore these and more applications of cell cultures in future units. Figure 6: Notice the flat culture bottles used for animal cultures. These bottles contain liquid media with all of the appropriate nutrients and hormones for a specific type of animal cell. The flat shape of the bottle allows for easy stacking and also allows cells to spread out in the media.

Bioreactors are often used for large batches of cell cultures. These devices include a chamber that is kept in specific conditions to optimize the growth of the cells in that culture.  Figure 7: This is an example of a bioreactor used for the large scale production of cell cultures. These are sometimes referred to as fermentation chambers, as they are often used for the growth of bacterial and fungal organisms which carry out the process of fermentation.

Tissue engineering methods are also being continually developed. In such experiments, a scaffold of a particular tissue or organ is made of biological substances to produce a scaffold. Cells are then placed on this scaffold in a step known as seeding. These “seed” cells will create more cells that will grow on the scaffold. Thus, if the scaffold was made to resemble a human urinary bladder, once the cells have grown on that scaffold you will have an engineered urinary bladder. Such experiments have resulted in the formation of human skin that can be used for human transplant.