Why does dna replicate exactly

Hope this helps! Feb 27, Primarily for cell division. Explanation: 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. Related questions Why does DNA polymerase proofread the new strand? Why are nucleotides added to 3' end? How does the base pairing rule affect DNA replication?

How does dna replication relate to mitosis? How does DNA polymerase work? 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. 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. Image credit: Genome Research Limited. Each genome contains all of the information needed to build that organism and allow it to grow and develop. DNA or deoxyribonucleic acid is a long molecule that contains our unique genetic code.

Like a recipe book it holds the instructions for making all the proteins in our bodies. Cells are the basic building blocks of living things. The human body is composed of trillions of cells, all with their own specialised function. 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?