1. DNA Replication

2. DNA Does 2 Important Things in a Cell: 1)DNA is capable of replicating itself. Every time a cell divides, each DNA strand makes an exact copy of itself. 2)DNA directs the production of proteins in the cell. DNA contains the instructions on how to make proteins.

3. The Cell Cycle During the S phase of Interphase, the DNA strands (chromosomes) are replicated.

4. Why does DNA replicate? DNA replication occurs once in the life of a cell—right before it divides into two daughter cells. DNA strands replicate so that each new daughter cell has its’ own copy of the DNA instructions.

5. DNA strands are anti-parallel The deoxyribose sugar has 5 carbons. Carbon 1 is attached to the nitrogen base. Carbons 3 and 5 are attached to Phosphate groups. These are called 5’ and 3’ ends.

6. DNA Replication, Step 1 1) Helicase unwinds the DNA molecule and opens up the hydrogen bonds between the base pairs. The place where the DNA is opening up is called the Replication Fork. Single-stranded binding proteins (SSBs) hold the DNA strands open.

7. DNA Replication, Step 2 DNA Polymerase adds nucleotides to the strands, one base at a time. The bases are added to their complimentary bases, according to the base-pairing rules: A bonds to T C bonds to G This will make 2 strands of identical DNA

8. DNA Replication—a few more details DNA polymerase cannot add nucleotides to an existing “open” strand by itself. First, a short piece of RNA (called a primer) must be added to the open strand by Primase. Later on, the RNA primer will be removed and replaced with DNA.

9. DNA Replication—More details DNA Polymerase can only add nucleotides in the 5’ to 3’ direction. Therefore, one of the new strands will be made continuously. This is called the leading strand. The other strand must be made in pieces called Okazaki fragments. This strand is called the lagging strand.

10. DNA Replication Diagram http://www.youtube.com/watch?v=teV62 zrm2P0 http://www.youtube.com/watch?v=teV62 zrm2P0

11. DNA Replication Animations http://www.youtube.com/watch?v=zdD kiRw1PdU&feature= related http://www.youtube.com/watch?v=zdD kiRw1PdU&feature= related http://www.wiley.co m/college/pratt/047 1393878/student/a nimations/dna_repli cation/index.html http://www.wiley.co m/college/pratt/047 1393878/student/a nimations/dna_repli cation/index.html

12. Quick Quiz What is the purpose of each of these enzymes? A. Helicase B. DNA Polymerase C. Single Stranded Binding proteins (SSBs) D. Primase Why does DNA replicate with a leading strand and a lagging strand—why don’t both strands replicate the same way?

13. Name each part of this diagram: