The process in which DNA is copied from a template to form copies of itself.

Every time a cell divides to produce another, it has to replicate (make a copy) of its DNA to pass on to the new cell.

How?

The DNA strand acts as a template for its own replication.

The secret is in the base pairs.

The sequence of bases in the old strand determines the sequence in the new strand.

The replication of DNA requires the work of a number of protein molecules, most of them called ENZYMES.Enzymes catalyze chemical reactions.They control the rate of reactions.

There is a small army of enzymes controlling DNA replication:1. The initiator protein2. Helicase (the “unzipper”)3. DNA Polymerase (the “builders”)4. Repair Nuclease (the “eraser”)5. Topoisomerase (the “untwister”)6. DNA binding proteins (the “straighteners”)7. Ligase (the “zipper” or “stitcher-upper”)

1. Enzyme (DNA Helicase) “unzips” the molecule by breaking the Hydrogen bonds that hold the base pairs together.

Helicase

2. Enzyme(RNA primase), starts the replication by matching up base pairs on the unzipped strands.

3. Enzyme (DNA polymerase) “reads” the unzipped molecule and brings in complementary base pairs to match up and complete the side it is reading.

This is done one nucleotide at a time, on both sides of the molecule.

Please click on these  Animations to view DNA replication!Animationshttp://www.johnkyrk.com/DNAreplic.swf

http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html

Once complete, the replicated DNA molecules each have One old strand and one new strand.

Do errors ever occur? Yes, it’s possible.But errors are remarkably rare!

Errors in the code are called mutations.When they occur, they can:a. helpb. harm c. have no effect

The only mutations that can be passed on to offspring are those that occur during the making of gamete cells.

Gametes carry mutations in the genetic code to the offspring of sexual reproduction.

Mutations in the genetic code account for the astounding diversity of life on this planet!!!

Mutations aren’t always bad, nor always good.They happen infrequently, because the code in the DNA sequence is copied accurately almost every time.