2. SEMI-CONSERVATIVE DNA REPLICATION Pages 333-335

3. Essential Questions replication What is replication and how is it done? helicaseDNA polymerase What’s the role of the enzymes helicase and DNA polymerase?

4. Replication When a complete copy of the DNA is made during the S-Phase of the cell cycle.

5. mitosis & cell division

6. WHY MUST DNA SYNTHESIZE COPIES OF ITSELF ? TO ENSURE THAT EVERY NEW CELL CONTAINS EXACTLY THE ______________ AND EXACTLY THE ____________ OF GENES THE PARENT CELL HAD. SAME NUMBER SAME KIND

7. The DNA code is in the middle of the helix, so how does it get copied if it’s obscured by the side chains and twist of the helix shape?

8. DNA Synthesis Step One: Hydrogen bonds are broken by the enzyme, Helicase.

9. Hydrogen Bonds are weak bonds = REVIEW: Hydrogen bonds are located between nitrogenous bases

10. Step Two: DNA Polymerase adds free nucleotides to both strands.

11. Step 3: New DNA strands are Proofread and mistakes are repaired:

12. 1.Helicase replication fork 1.Helicase enzyme “unzips” the double helix by weakening H-bonds creating a replication fork where the two DNA chains separate. 2.DNA polymerase 2.DNA polymerase enzyme assembles new DNA nucleotides using each original strand as a template. 3.The replicated DNA is proofread and any mistakes are edited. ReplicationReplication occurs in 3 Steps:

13. Replication Fork

14. Leading and Lagging Strands The leading strand is the strand of DNA that is made continuously. The lagging strand is the strand of DNA that is made discontinuously.

15. Boring person explaining http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535 ::535::/sites/dl/free/0072437316/120076/mic ro04.swf::DNA%20Replication%20Fork http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535 ::535::/sites/dl/free/0072437316/120076/mic ro04.swf::DNA%20Replication%20Fork

16. Replication is Discontinuous on the Lagging Strand Okazaki fragments  Short fragments of DNA called Okazaki fragments are created near the replication fork. DNA polymerase  Gaps are filled in when DNA polymerase adds nucleotides.  Bases are added following the base pairing rules (A-T, C-G) * The lengths of Okazaki fragments are between 1,000 to 2,000 nucleotides long in bacteria and are generally between 100 to 200 nucleotides long in eukaryotes.

17. DNA Foldables 1/4 1/2

18. Copy the following sequence onto your foldable on the left side. Write the new base pairs on the right side. T--A--C--A--A--A--C--T--T--A--C--T----A--T--G--T--T--T--G--A--A--T--G--A Remember that H-bonds hold complementary bases together

19. Unzip sequence on your foldable. TACAAACTTACTATGTTTGAATGA Helicase Step 1: Helicase enzyme “unzips” double helix by weakening H-bonds

20. Using the original DNA sequence on the foldable make a copy. TACAAACTTACT ATGTTTGAATGA DNA polymerase Step 2: DNA polymerase enzyme adds DNA bases to the exposed nucleotides on the leading strand ATGTTTGAATGA

21. Using the original DNA sequence on the foldable make a copy. TACAAACTTACT ATGTTTGAATGA Okazaki fragments While Okazaki fragments are added on the lagging strand ATGTTTGAATGA ACA AC ACT

22. Using the original DNA sequence on the foldable make a copy. TACAAACTTACT ATGTTTGAATGA Polymerase Step 3: Polymerase also proofreads and edits any gaps ATGTTTGAATGA TACAAACTTACT

23. RESULTS TWO strands of identical DNA DNA replication is semiconservative because each new DNA molecule contains one original strand and one newly made strand.

25. original double helix original double helix Replication fork replication fork free nucleotides are attracted to their opposites forming two new strands two identical new strands are formed two identical new strands are formed

26. 4. During which phase of the cell cycle does DNA replicate? 5. Explain the process of DNA replication 1.Why must DNA synthesize copies of itself? 2. If the code below is for a parent DNA molecule, write the code for the offspring: AATTCCGGTATACCCGCCAAG 3. List and describe the three steps in the process of DNA replication.

27. Have Your DNA & eat it too! 1.Now replicate the DNA, using 2 more pieces of licorice but use black sticks

28. 3-2-1 3 steps cells undergo in replication 2 words meaning the structure of DNA 1 word for duplicating cell DNA