As you probably know, mitosis is what happens in cell division before the one cell finishes dividing into two new cells. The DNA is basically a recipe book. It contains directions for making all the proteins that make us work. Proteins include most of the structures that give us shape and strength, the enzymes that control our countless chemical reactions. Some of our hormones, antibodies that fight disease, and lots more.

Each cell has the complete set of instructions, but if it’s going to divide, each of the new cells needs its own set. Imagine that you are part of a team that is following directions to do something like put together a bunch of chairs. Let’s say your team decides to split up and work in two smaller teams. Each team will need its own set of directions. You would probably take a picture or take them to a photocopier. In a cell, the DNA is copied when a bunch of enzymes helps to synthesize (make) new DNA strands.

Sometimes a mistake is made in copying the DNA. This is called a mutation. The mutation may be good, bad, or neither one. These mutations are the raw material for natural selection because they create genetic variation in a population.

What kinds of cells do you think divide a lot? Which ones don’t divide at all?

During mitosis, the cell creates a second copy of itself. Prior to duplicating its DNA, the cell also duplicates all of its organelles. In its normal state, a human cell has 23 pairs of chromosomes. During mitosis, that number becomes 46 homologous pairs. This is so that each cell ends up with 23 pairs of chromosomes following cell division. If the cell did not duplicate its DNA (something that happens during meiosis to produce gametes), then each daughter cell would only receive one copy of each chromosome. Instead of having 23 pairs, the cells would each have 23 chromosomes (in other words, each cell would be haploid).

Mitosis is the process by which somatic (non-reproductive) cells divides. It produces two daughter cells which are identical to each other and to the original cell. These new cells replace old and damaged cells with new ones. The vast majority of cells in any organism are somatic cells, and many have specialized functions like those making up heart muscles and neurons. Because the daughter cells are supposed to fulfill the same special function as the parent, they need to be programmed the same way so they can grow and mature properly.

DNA contains this programming in the sequence of the bases which make up each chain. Thus, to ensure that the daughters can fulfill their role, the parent cell makes sure each receives a full set of instructions.

While it is conceivable that each daughter cell could receive a single strand of DNA from the parent and then produce the complementary strand, there are a number of reasons this would not be favorable. These range from potentially compromising the genetic sequence (the double strand of DNA is more stable than a single strand and also allows checking of the code ) to being an inefficient use of energy.

If the DNA weren't duplicated, then there wouldn't be enough to give to each daughter cell, which would mean that the cells produced wouldn't have enough DNA to survive.

DNA replication during mitosis is extremely important. Since one cell is turning into two, it’s important that they each get their own sets of DNA after they split. Imagine you are a cell and you’re holding the book of DNA. That book contains the building blocks of everything you need to be a cell; it tells you exactly what to do all day and when. If you underwent mitosis to create another duplicate cell, you would want that cell to also have the book of DNA. Therefore, you’d have to make copies of all the pages you have and give them to the new cell before he departs, otherwise the new cell wouldn’t know how to function.

Every cell needs to have the proper amount of DNA, so when 1 cell divides into 2 cells during mitosis, it needs to have 2 copies of all the DNA.