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Replication
The next question to consider is how the DNA allows for growth and reproduction.
Growth
Plants and animals grow by having each cell divide to make two cells. These new cells
divide to make more cells and so on. Each new cell must have a new identical set of DNA
molecules. The process of making more DNA for the new cells is called replication.
| We start the process with an intact double strand of DNA. |
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| Next, the DNA molecule splits and the strands separate. |
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| With the help of an enzyme, each of the bases is paired up with its
corresponding base pair (which, of course, is bonded to a sugar and a phosphate). Adenine
gets a thymine, cytosine gets a guanine, and so on. The phosphate of one nucleotide is
attached to the sugar (deoxyribose) of the adjacent nucleotide, one after another. |
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| This happens with both strands, and when the process is complete, we have
two DNA molecules, one just like the other. At this point, the cell can divide, and
each new cell gets its own set of DNA molecules. |
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If the newly formed cell stays stays in the same organism this is growth. That organism
is now larger than it was.
| Cell division is used for both growth and reproduction. If the new cells
stay with the existing organism, that is growth. If the new cells split away to form a new
organism, that is reproduction (a new geration is formed). In either case, the new cells
will have DNA from the original cell. Replication of DNA results in a complete set of DNA
for each of the new cells. However, replication of DNA does not always occur when cells
divide. |
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New Generations
How is genetic information transferred to a new generation? That depends, in part, on
the nature of the plant or animal or other living thing that's being considered. There are
a variety of ways this can occur, such as cell division, plant starts, regeneration, or
cloning. New cells can be created, with new DNA molecules, in the process earlier
described as growth. If the cells separate and form a new organism then that is
reproduction rather than growth (or along with growth since things keep happening).
| Many creatures, including humans, have two sets of genes (two sets of DNA,
shown here as black and red). Diploid is the biological term. When cells in these plants
and animals split, they can do so in one of two ways. They can replicate their double set
of DNA (growth, shown above) or they can separate their two sets of DNA and make cells
with one set of DNA (shown here). Haploid is the biological term. This is done in
preparation for reproduction. |
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| In humans and many other species these cells can fuse with cells from
another individual to create a new generation with a new double set of
genes (DNA) and the growth process resumes. In some species, however, those cells with
just one set of genes will grow and replicate before the fusion occurs. In a sense, they
constitute their own generation, but I have digressed. |
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Let's get back to the chemistry of these things on the next page.
Top of Page
E-mail instructor:
Sue Eggling
Clackamas Community College
©2001, 2003 Clackamas Community College, Hal Bender
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![Diagram representing a double strand of DNA. [69049.jpg]](images/69049.jpg)
![Diagram representing a split double strand of DNA. [69050.jpg]](images/69050.jpg)
![Diagram representing a split double strand of DNA with complentary strand being added. [69051.jpg]](images/69051.jpg)
![Diagram representing two double strands of DNA. [69052.jpg]](images/69052.jpg)
![Diagram representing cell division with replication. [celldiv1.gif]](images/celldiv1.gif)
![Diagram representing cell division without DNA replication. [celldiv2.gif]](images/celldiv2.gif)
![Diagram representing cell division without DNA replication, followed by fusion of cells. [celldiv3.gif]](images/celldiv3.gif)