The Functions of DNA

1. DNA has to replicate itself How does it make an exact copy?

DNA is made up of two complementary strands

DNA replication First the strands “unzip” at certain spots

Enzyme helicase unzips DNA

Then complementary bases pair up along each strand

Enzyme DNA polymerase adds complementary nucleotides to each strand

Semi-conservative replication Now two identical molecules of DNA exist where there was one before Each molecule contains one strand of the original DNA

When does DNA replication occur? Every time a cell divides--so that each cell will have all the instructions needed to produce proteins to do the cellular work

Cells divide to: 1.Repair worn or damaged cells

Cells divide to: 2. grow We each started as a single cell but once grown we have 100 trillion cells

Cells divide to: Reproduce! In asexual reproduction of single celled organisms, a new organism is created by simply dividing in two So the organism must replicate its DNA and its organelles as well in order to end up with two exactly identical cells

Cell division is also part of sexual reproduction Although it’s a more complicated form of cell division, DNA replicates in order to form egg and sperm cells