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DNA replication, the process by which genetic information is duplicated, occurs in order to ensure that each cell in an organism has a complete and correct copy of the organism's genome, or "library" of genetic data. This occurs during each instance of cell division, the process by which a single cell divides into two cells. DNA, or deoxyribonucleic acid, is a chemical chain that exists in the shape of a double helix. The arrangement of the component parts, or nucleotides, of DNA provide coded instructions that govern almost every process that occurs within an organism. The process of DNA replication ensures that each cell contains a copy of these instructions and is, accordingly, able to function correctly within the organism.
At the most basic level, the purpose of this process is to duplicate the DNA within each cell during every cycle of cell division. One of the most important parts of this process is error checking and correction. A cell's DNA contains the instructions that govern the cell's protein production, growth, positioning, and many other factors. Even slight errors in replication can cause potentially harmful changes in the cell's behavior. As such, extensive and redundant error checking mechanisms are built into the replication process, ensuring that, despite the fact that replication occurs in many cells in the body at any given moment, errors are very rare.
DNA replication occurs in two different forms of cellular division. The first is mitosis, which serves all of the normal needs of growth, maintenance, and repair within an organism. In mitosis, a single cell divides into two, each with its own set of genetic information. A second type of cell division known as meiosis occurs to produce sex cells, such as egg and sperm cells. In this context, DNA replication occurs in order to supply the cells resulting from meiosis with genetic information to pass on to offspring.
Some laboratory experiments require large-scale DNA replication of specific sequences of DNA rather than of an organism's entire genome. The process used to cause such large-scale DNA replication is referred to as a polymerase chain reaction, or PCR. A few copies of a particular sequence of DNA can be replicated many times until the number of copies of the sequence has increased by several orders of magnitude. This laboratory replication technique allows scientists to study particular sequences of DNA for a variety of purposes, including gene sequencing and diagnosis of genetic disorders.
@umbra21 - They take advantage of that function in cancer cells when they grow human cells for laboratory testing.
Most of the cells used in lab testing were originally samples from cancer patients, where it was discovered that the sample just continues to grow without the DNA replication process eventually breaking down, like it does with normal cells.
I know there's one particular strain of cells that's been going since the 1960's. The woman who was the original donor of the cells is long gone, but because her DNA was faulty her cells continue to live on today.
It's a bit creepy on the one hand, but on the other hand, you're right in that it could eventually lead to humans being able to live for a very long time.
@browncoat - Well, you also have to consider that DNA replication isn't perfect. Even when you have identical twins, they often have genetic differences, which I think can skew those studies, making it even more likely that genetics is a huge factor in a lot of cases.
What I find interesting about DNA replication is that there is actually a mechanism in the process which prevents it from happening too many times. Eventually the cell is forced to stop.
When this process gets corrupted it can lead to cancer, for example, because the cells won't die when they are supposed to, to make way for other cells.
But scientists are also looking into this process to see if it can help
people live longer, since part of what makes us age is that certain cells, particularly in the brain, stop replicating DNA and start to die off.
If they can one day find a way to change this, without causing cancerous growths then in theory, a person could live almost indefinitely.
My friend and I were just talking today about the whole nature versus nurture debate. I tend to think that people are quite influenced by the genes they inherit from their parents.
My friend thought it was more to do with how a person is influenced as they grow up.
Actually there's quite a bit of science on my side, as there have been numerous twin studies showing that even personality has more to do with what your chromosomes look like than what kind of situation you grow up in.
Of course, you can always use extreme examples like people growing up in abusive homes and so forth to make the argument that environment causes just as much influence. It's difficult to know for sure.