DNA Replication

When does DNA replication happen during the cell cycle? The S phase In order to go through cell division we must have two copies of DNA The process of replication assures that each new cell made has a complete set of identical genetic information. With out replication, our cells would not be able to perform their function correctly

Are the two strands of DNA considered to be complementary to one another? YEP! Since A binds with T and C binds with G, they are always opposite one another. –Meaning if one side is ACACACAC then the other strand is TGTGTGTG. Being complementary to one another allows each strand to serve as a TEMPLATE for a new strand! This characteristic is important for the process of replication. 5’ 3’

What does the 5’ and 3’ mean on the DNA strands? Because DNA strands are complementary (opposite one another) we have to be able to determine the top from the bottom. This is done by marking it as a 5’ prime or 3’ prime end. This also helps determine the direction of replication on the DNA strand Replication ALWAYS starts at the 5’ prime end 5’ 3’

Steps to DNA Replication Replication can be studied as 3 steps (although all occur simultaneously in the cell) Although people may say that DNA copies itself, the DNA itself does nothing more than store information. Enzymes and other proteins do the actual work of replication –Helicase starts the process by unzipping the double helix to separate the strands –DNA polymerase bonds new nucleotides together

Step 1 The enzyme Helicase begin to unzip the double helix at numerous places along the chromosome –That is Hydrogen bonds that connect the base pairs are broken

Step 1 As the strands separate, the bases on each strand are exposed for the next step (happening simultaneously) Unlike unzipping a jacket, replication proceeds in two directions at the same time. nucleotide The DNA molecule unzips in both directions.

Step 2 DNA polymerase, another enzyme, creates the daughter strands by adding complementary bases to the parent strands (which act as a template). DNA polymerase new strand nucleotide

Step 3 The two developing DNA strands separate into two new, identical daughter strands and DNA polymerase proofreads them. (Label the parts below on your notes) New Strand Original Strand original strand new strand Two molecules of DNA

There are many origins of replication in eukaryotic chromosomes. DNA replication starts at many points in eukaryotic chromosomes. Replication is fast and accurate. DNA polymerases can find and correct errors.

In every living thing, DNA replication happens over and over again, and it happens remarkably fast. In humans, about 50 nucleotides are added every second to a new strand of DNA Your DNA has replicated trillions of times since you grew from a single cell.

Real Picture of DNA replication