1. Teacher Notes  This PPT was revised June 25, 2007.  This PPT is a companion PPT to Mitosis & Meiosis.  There is a handout for this PPT.

2. Reproduction & DNA Replication How does DNA copy itself?

3. Mitosis – Why Divide?  to increase surface area  to repair damaged cells  to grow

4. Cell Reproduction Cells reproduce either sexually or asexually. Bacteria

5. ant 2 chromosomes Chromosome Number  Every species has a specific number of chromosomes that every body cell is supposed to have. crayfish 200 chromosomes human 46 chromosomes dog 78 chromosomes

6. Chromosome Number  Since you inherit half of your chromosomes from each parent, you carry two complete sets of chromosomes. mother crayfish 100 chromosomes father crayfish 100 chromosomes 1 set of 100 2 sets = 200 crayfish 200 chromosomes

7. Chromosome Number  The single set of one chromosome of each type inherited from one parent is called haploid.  Haploid: 1 set of chromosomes (n) found in gametes (egg or sperm) 23 Chromosomes

8. Chromosome Number  A cell (such as a fertilized egg) with two sets of homologous chromosomes is called diploid.  Diploid: 2 sets of chromosomes (2n) found in body cells (somatic) 46 chromosomes

9. Chromosome Number  Recall that every body cell in an organism must have the specific 2n chromosome number for that species.  If it doesn’t, the cell will not be able to function properly. humans must have 46 chromosomes

10. How does this happen?  When we grow by our cells dividing to make two new cells, all of those new cells must have 46 chromosomes.  How do we get 92 chromosomes (46 for each new cell) from a cell with only 46 chromosomes? 46

11. Chromosome Number  The doubling of the chromosomes is actually DNA making an exact copy of itself. This is called DNA replication. 46 Then each new cell can receive the correct number of chromosomes (DNA). 4692

12. A Cell’s Life Cycle  When does a cell divide?  Most of a cell’s life cycle is spent in Interphase when it performs normal life functions M G1G1 S G2G2 C G1G1

13. A Cell’s Life Cycle  When does a cell divide? M G1G1 S G2G2 C Only a small part of the cell cycle is spent in division. The RED section marked letter M

14. A Cell’s Life Cycle  When does DNA replication occur?  During Interphase, just before division, the DNA replicates (makes a copy of itself). M G1G1 S G2G2 C G1G1

15. DNA Replication  Before a cell divides the DNA must replicate (make an exact copy of itself) so the new cells have the right 2n # of chromosomes.

16. DNA Replication  Each new cell must have the same chromosome number (and same DNA) as the parent cell to function properly.

17. DNA Replication  Replication occurs in 3 easy steps…

18. DNA Replication A. DNA Unzips  An enzyme called DNA Helicase unzips the molecule by breaking the hydrogen bonds that hold the nitrogen bases together.

19. DNA Replication: 1. DNA Unzips 3’End 5’End A T A G G C 3’End 5’End A T T C C G Left 5’ Strand of Original DNA Right 3’ Strand of Original DNA 5” End

20. The point where the original DNA strand separates is called the replication fork

21. B. Bases Pair  An enzyme called DNA Polymerase adds complementary bases to bond with each original base in the open helix  What is the complementary base pairing rule?  A = T  G  C

22. DNA Base Pairing – Step 2 3’End 5’End A T AG G C 3’End 5’End A T T C C G T C A GG C A T G T A C

23. C. Two Identical DNA molecules  Two new DNA molecules each have the same DNA nitrogen base sequence.  The new DNA molecules are exactly like the original. T C C A G G T C C A G G T C C A G G

24. DNA Replication Review  Explain what is happening at each step in DNA Replication. Step 1 Step 2 Step 3

26.  What molecule is at I? Original DNA DNA Replication Review  What process is occurring? DNA replication  What is happening at II (the arrow)? Replication fork  What are the structures at III (circle)? Free nucleotides I II V V III IV

27.  What are the 2 molecules at V? identical DNA DNA Replication Review  What is happening at IV?? Complementary base-pairing  How many strands are formed? I II V V III IV  What are the new strands like compared to the original? identical  What are the new strands like compared to each other? identical

28. MITOSIS  Now that DNA has replicated, Mitosis (cell division) can begin.  The cell now has two identical sets of DNA/chromosomes. 46 92 T C C A G G T C C A G G

29.  What is the purpose of DNA replication? make identical copies of DNA

30. TRY THIS!  On your paper create a 3 Column Chart for Cell Reproduction and DNA Replication What I Know…What I Don’t Know… What I Wish I Knew…

31. Works Cited  There is a nice animation of DNA Replication at http://www.ncc.gmu.edu/dna/repanim.htm http://www.ncc.gmu.edu/dna/repanim.htm  DNA Replication diagram, artist Darryl Leja, National Human Genome Research Institute (NHGRI) http://www.genome.gov/page.cfm?pageID=10000552http://www.genome.gov/page.cfm?pageID=10000552  Background DNA Replicaiton image, DOE Human Genome project, Department of Energy, (http://www.ornl.gov/hgmis)  DNA Replication diagram, artist Darryl Leja, National Human Genome Research Institute (NHGRI) http://www.genome.gov/page.cfm?pageID=10000552http://www.genome.gov/page.cfm?pageID=10000552  “Fertilization - sperm fertilizing egg”, (No Date). Wikipedia.com, Retrieved June 20, 2006 from the World Wide Web: http://en.wikipedia.org/wiki/Image:Fertilisation.jpg, Website Copyright Permission: This image is copyrighted. However, the copyright holder has irrevocably released all rights to it, allowing it to be freely reproduced, distributed, transmitted, used, modified, built upon, or otherwise exploited in any way by anyone for any purpose, commercial or non-commercial, with or without attribution of the author, as if in the public domain.copyrighted