Why replicate dna

Which is all the more amazing considering that there are almost three billion base pairs of DNA to be copied. Replicating all of the DNA in a single human cell takes several hours of just pure copying time. At the end of this process, once the DNA is all replicated, the cell actually has twice the amount of DNA that it needs, and the cell can then divide and parcel this DNA into the daughter cell, so that the daughter cell and the parental cell in many case are absolutely genetically identical.

This primer permits the next step in the replication process. The sugar-phosphate backbones of each strand are depicted as a segmented grey cylinder. Nitrogenous bases on each strand are represented by blue, orange, red, or green horizontal rectangles attached to each segment of the sugar-phosphate backbone.

The bases form rungs of red-green or blue-orange between the grey cylinders. Helicase is bound to the ends of several nitrogenous bases on the lower strand. Beside it, four nitrogenous bases, each attached to a sugar molecule, have been annealed to complementary nitrogenous bases on the bottom strand. About three dozen individual nucleotides float in the background.

Meanwhile, as the helicase separates the strands, another enzyme called primase briefly attaches to each strand and assembles a foundation at which replication can begin. This foundation is a short stretch of nucleotides called a primer Figure 2.

As DNA polymerase makes its way down the unwound DNA strand, it relies upon the pool of free-floating nucleotides surrounding the existing strand to build the new strand. The nucleotides that make up the new strand are paired with partner nucleotides in the template strand; because of their molecular structures, A and T nucleotides always pair with one another, and C and G nucleotides always pair with one another.

This phenomenon is known as complementary base pairing Figure 4 , and it results in the production of two complementary strands of DNA. Base pairing ensures that the sequence of nucleotides in the existing template strand is exactly matched to a complementary sequence in the new strand, also known as the anti-sequence of the template strand.

Later, when the new strand is itself copied, its complementary strand will contain the same sequence as the original template strand. Thus, as a result of complementary base pairing, the replication process proceeds as a series of sequence and anti-sequence copying that preserves the coding of the original DNA. In the prokaryotic bacterium E. In comparison, eukaryotic human DNA replicates at a rate of 50 nucleotides per second.

In both cases, replication occurs so quickly because multiple polymerases can synthesize two new strands at the same time by using each unwound strand from the original DNA double helix as a template. One of these original strands is called the leading strand, whereas the other is called the lagging strand.

The leading strand is synthesized continuously, as shown in Figure 5. In contrast, the lagging strand is synthesized in small, separate fragments that are eventually joined together to form a complete, newly copied strand.

This page appears in the following eBook. Here is a video which uses an animated tutorial to explain the process of DNA replication. Basically, every time a cell undergoes mitosis one kind of cell division , various enzymes work to split each DNA strand in half, and then replace the missing half on the separated strands with corresponding nucleotides, leaving you with two identical strands. When the entirety of a cell's genome is copied along with all the organelles , the cell can split into two daughter cells.

Imagine slicing yourself down the middle and splitting yourself in half, and then using each half of you as a template to recreate the other half. That's the biology behind it, but the bottom line is that DNA is replicated in order to reproduce itself. Why does DNA replication need to occur? Mar 24, If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website? Open survey. In: Facts In the Cell.

This is carried out by an enzyme called helicase which breaks the hydrogen bonds holding the complementary bases of DNA together A with T, C with G. The two separated strands will act as templates for making the new strands of DNA.