Bell Ringer: Have your vocabulary numbered on the side of your desk! 1-How are base pairing rules related to Chargaff’s research on DNA? 2-In a sample of yeast DNA 31.5% of the bases are adenine. Predict the approximate percentages of C, G, and T. 3-How many rings are there on each base pair?

KEY CONCEPT DNA replication copies the genetic information of a cell.

REPLICATION = DNA making DNA original strand new strand Two molecules of DNA

Replication copies the genetic information. A single strand of DNA serves as a template for a new strand. The rules of base pairing direct replication. DNA is replicated during the S (synthesis) stage of the cell cycle. Each body cell gets a complete set of identical DNA.

Proteins carry out the process of replication. DNA serves only as a template in a three step process. nucleotide The DNA molecule unzips in both directions.

Enzymes and other proteins do the actual work of replication. DNA polymerases are proteins (enzymes) that form bonds between nucleotides during replication. DNA poly = tells us it makes DNA polymers Ases = tells us its an enzyme

The DNA molecule unzips in both directions. Step ONE Enzymes unzip the double helix an numerous places along the chromosome. (these places are called origins of replication) This means the hydrogen bonds connecting base pairs are broken, the original molecule separates, and the bases on each strand are exposed. This process proceeds in two directions at one time. nucleotide The DNA molecule unzips in both directions.

Step TWO: Free-floating nucleotides pair, one by one, with the bases on the template strands as they are exposed. DNA polymerases bond the nucleotides together to form new strands that are complementary to each template strand. DNA polymerase new strand nucleotide

STEP THREE Two new molecules of DNA are formed, each with an original strand and a newly formed strand. DNA replication is semiconservative. (one old and one new strand) original strand new strand Two molecules of DNA

Replication is fast and accurate. DNA replication starts at many points in eukaryotic chromosomes. The replication “bubbles grow larger as replication progresses. There are many origins of replication in eukaryotic chromosomes. DNA polymerases can find and correct errors.

DNA replication takes about eight hours in human cells DNA replication takes about eight hours in human cells. If there were only one origin the process would take about a hundred times longer.

Question In step 1 how does the DNA unzip?

Question In step 2, how do the new strands compare with the template strands?

Question What is the result of DNA replication?

Question Why is it important for the cell to correct any errors that occur during replication?