Why do cells duplicate their dna

And during that process of cell division, all of the information in a cell has to be copied, and it has to be copied perfectly. And so DNA is a molecule that can be replicated to make almost perfect copies of itself. Which is all the more amazing considering that there are almost three billion base pairs of DNA to be copied. DNA is the essential stuff of beginnings. Its double strands -- which consist of chemical 'letters' or base pairs -- tell cells how to remake themselves; how to build the protein machines that keep them alive and make them distinct.

So before they divide, cells have to duplicate their DNA. This is a relatively straightforward affair for bacteria and other simple cells, also called prokaryotes since they typically only have a single loop of DNA, even though it can be millions of base pairs long. As a consequence, they have just a single point along the strand where the copying starts, called an origin of replication. However, most of biology that can be seen with the naked eye -- animals and plants and even humble yeast -- is composed of more complicated cells called eukaryotes.

Eukaryotes have much more DNA, which is tightly wound into distinct pieces, or spindles, called chromosomes, each of which may have many origins of replication. So in order to finish in a reasonable amount of time, those cells have to begin copying their DNA simultaneously at tens of thousands of different points. But how do they begin? 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. Aa Aa Aa. How is DNA replicated? What triggers replication? Figure 1: Helicase yellow unwinds the double helix. The initiation of DNA replication occurs in two steps. First, a so-called initiator protein unwinds a short stretch of the DNA double helix.

Then, a protein known as helicase attaches to and breaks apart the hydrogen bonds between the bases on the DNA strands, thereby pulling apart the two strands. As the helicase moves along the DNA molecule, it continues breaking these hydrogen bonds and separating the two polynucleotide chains Figure 1.

How are DNA strands replicated? Figure 3: Beginning at the primer sequence, DNA polymerase shown in blue attaches to the original DNA strand and begins assembling a new, complementary strand. At this point the cell checks itself again, makes sure it is big enough and ready to go into the M phase.

M phase stands for mitosis which is where the cell goes through a lot of complex steps in order to split into two daughter cells. Since the cell cycle is a circle, both daughter cells can then move straight into G 1 phase to start the cycle all over again. The cell cycle can be a really difficult idea to wrap your head around but asking questions like these is the first step toward understanding science better. Thanks for the question! Cells duplicate DNA during interphase , usually shortly before entering either mitosis or meiosis eukaryotic cells or fission prokaryotes.

When do cells duplicate their DNA? Answer 1: The short answer is before they divide. Mitosis is the process where the DNA gets divided evenly between the two halves of a cell. Then the cell actually splits. The split is called cytokinesis.