Describe how DNA is able to make an exact copy of itself when a cell splits into two new cells?

Question

Describe how DNA is able to make an exact copy of itself when a cell splits into two new cells?

Answer 1

DNA Replication

DNA carries the information for making all of the cell's proteins. These proteins implement all of the functions of a living organism and determine the organism's characteristics. When the cell reproduces, it has pass all of this information on to the daughter cells.

Before a cell can reproduce, it must first replicate, or make a copy of, its DNA. Where DNA replication occurs depends upon whether the cells is a prokaryote or a eukaryote (see the RNA sidebar on the previous page for more about the types of cells). DNA replication occurs in the cytoplasm of prokaryotes and in the nucleus of eukaryotes. Regardless of where DNA replication occurs, the basic process is the same.

The structure of DNA lends itself easily to DNA replication. Each side of the double helix runs in opposite (anti-parallel) directions. The beauty of this structure is that it can unzip down the middle and each side can serve as a pattern or template for the other side (called semi-conservative replication). However, DNA does not unzip entirely. It unzips in a small area called a replication fork, which then moves down the entire length of the molecule.

Let's look at the details:

   1. An enzyme called DNA gyrase makes a nick in the double helix and each side separates

   2. An enzyme called helicase unwinds the double-stranded DNA

   3. Several small proteins called single strand binding proteins (SSB) temporarily bind to each side and keep them separated

   4. An enzyme complex called DNA polymerase "walks" down the DNA strands and adds new nucleotides to each strand. The nucleotides pair with the complementary nucleotides on the existing stand (A with T, G with C).

   5. A subunit of the DNA polymerase proofreads the new DNA

   6. An enzyme called DNA ligase seals up the fragments into one long continuous strand

   7. The new copies automatically wind up again