1. Cell Division Binary Fission, Mitosis & Meiosis

2. Binary Fission Most cells reproduce through some sort of Cell DivisionMost cells reproduce through some sort of Cell Division Prokaryotic cells divide through a simple form of division called Binary FissionProkaryotic cells divide through a simple form of division called Binary Fission 3 step process3 step process Single “naked” strand splits and forms a duplicate of itself.Single “naked” strand splits and forms a duplicate of itself. The two copies move to opposite sides of the cellThe two copies move to opposite sides of the cell Cell “pinches” into two new and identical cells called "daughter cells". (Cell wall then forms if applicable)Cell “pinches” into two new and identical cells called "daughter cells". (Cell wall then forms if applicable)

3. Mitosis Eukaryotes divide by a more complicated system called MitosisEukaryotes divide by a more complicated system called Mitosis This is because:This is because: 1.They have a nucleus which must be broken up and then reformed 2.They have their DNA “packaged” in the form of Chromosomes 3.Chromosomes are composed of Chromatin 1.Made of DNA Strands & Proteins 4.Also contain Nucleosomes containing Histones - Proteins the DNA is wrapped around Name for the DNA/Protein complex is Chromatin 5.They usually have more than 1 chromosome (Humans have 23 pairs) 6.They have numerous organelles to equally share

4. Chromatin / Chromosomes

5. The Cell Cycle Most of the cell's life is spent doing its regular function.Most of the cell's life is spent doing its regular function. Cells divide along a rough time frame called its Cell Cycle.Cells divide along a rough time frame called its Cell Cycle. The Cell cycle consists of the folowing steps:The Cell cycle consists of the folowing steps: G1 (Gap 1) Phase - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span)G1 (Gap 1) Phase - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span) S (Synthesis) Phase - Here the cell actively duplicates its DNA in preparation for divisionS (Synthesis) Phase - Here the cell actively duplicates its DNA in preparation for division G2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases in preparation for division.G2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases in preparation for division. Mitosis - Actual division occursMitosis - Actual division occurs

6. Interphase Cell Replicates its DNA/Chromosomes in preparation of upcoming divisionCell Replicates its DNA/Chromosomes in preparation of upcoming division Animal Cell Plant cell

7. Mitosis is a continuum of changes. –For description, mitosis is usually broken into five subphases: prophase, prometaphase, metaphase, anaphase, and telophase. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. By late interphase, the chromosomes have been duplicated but are loosely packed. The centrosomes have been duplicated and begin to organize microtubules into an aster (“star”). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5a

9. In prophase, the chromosomes are tightly coiled, with sister chromatids joined together. The nucleoli disappear. The mitotic spindle begins to form and appears to push the centrosomes away from each other toward opposite ends (poles) of the cell. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5b

10. During prometaphase, the nuclear envelope fragments and microtubules from the spindle interact with the chromosomes. Microtubules from one pole attach to one of two kinetochores, special regions of the centromere, while microtubules from the other pole attach to the other kinetochore. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5c

11. The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate, an imaginary plane equidistant between the poles, defining metaphase. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5d

12. At anaphase, the centromeres divide, separating the sister chromatids. Each is now pulled toward the pole to which it is attached by spindle fibers. By the end, the two poles have equivalent collections of chromosomes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5e

13. At telophase, the cell continues to elongate as free spindle fibers from each centrosome push off each other. Two nuclei begin to form, surrounded by the fragments of the parent’s nuclear envelope. Chromatin becomes less tightly coiled. Cytokinesis, division of the cytoplasm, begins. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5f

14. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5 left

15. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5 right

16. Prophase 1.Chromosomes Shorten and become visible. 2. Centrioles move to opposite sides of the cell 3. Nuclear envelope disappears 4. Spindle Fibers & Astral Fibers both together are known as the Spindle Apparatus begin to form Animal Cell Plant Cell

17. Metaphase Chromosomes line up along center of cell called the Metaphase PlateChromosomes line up along center of cell called the Metaphase Plate Chromosomes attach to spindle fibersChromosomes attach to spindle fibers Spindle & Astral fibers are now clearly visibleSpindle & Astral fibers are now clearly visible Animal Cell Plant Cell

18. Anaphase Centromeres break up separating chromosome copies Chromosomes are pulled apart to opposite sides of cell Spindle & Astral fibers begin to break down Animal Cell Plant Cell

19. Telophase (cytokenesis) Nuclear envelope forms around both sets of chromosomesNuclear envelope forms around both sets of chromosomes DNA uncoilsDNA uncoils Spindle & Astral fibers completely disappearSpindle & Astral fibers completely disappear –Cytokenesis happens with most (but not all) cells –Cytoplasm & organelles move (mostly equally) to either side of the cell.Cell Membrane “pinches” to form 2 separate cells Animal Cell Plant Cell

20. Animal Cytokeneisis Cytokenesis differs significantly between Animal & Plant cells. With animals, the membranes pinch together to form a Cleavage Furrow, which eventually fuses to form two daughter cells

21. Plant Cytokenesis With Plants, a cell wall must be formed between the 2 daughter cells. Vessicles containing Cellulose form and fuse between the tow daughter cells, eventually forming a complete cell wall.

22. Overview of Mitosis

23. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.9

24. Meiosis Similar in many ways to mitosisSimilar in many ways to mitosis Several differencesSeveral differences Involves 2 cell divisionsInvolves 2 cell divisions Results in 4 cells with 1/2 the normal genetic informationResults in 4 cells with 1/2 the normal genetic information

25. Vocabulary Diploid (2N) - Normal amount of genetic materialDiploid (2N) - Normal amount of genetic material Haploid (N) - 1/2 the genetic material.Haploid (N) - 1/2 the genetic material. Meiosis results in the formation of haploid cells.Meiosis results in the formation of haploid cells. In Humans, these are the Ova (egg) and sperm.In Humans, these are the Ova (egg) and sperm. Ova are produced in the ovaries in femalesOva are produced in the ovaries in females Process is called oogenesisProcess is called oogenesis Sperm are produced in the testes of males.Sperm are produced in the testes of males. Process is called spermatogenesisProcess is called spermatogenesis

26. Meiosis Phases Meiosis occurs in 2 phases; Meiosis I, & Meiosis II. Meiosis I. –Prior to division, amount of DNA doubles

27. Crossing Over During metaphase 1 homologous chromosomes line-up along the metaphase plateDuring metaphase 1 homologous chromosomes line-up along the metaphase plate Areas of homologous chromosomes connect at areas called chiasmataAreas of homologous chromosomes connect at areas called chiasmata

28. Crossing over contd. Crossing Over of genes occurs nowCrossing Over of genes occurs now –Segments of homologous chromosomes break and reform at similar locations. –Results in new genetic combinations of offspring. –This is the main advantage of sexual reproduction

29. Chromosome reduction During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK.During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK.

30. Meiosis I continued Nuclei may or may not reform following division.Nuclei may or may not reform following division. Cytokenesis may or may not occurCytokenesis may or may not occur

31. Meiosis II DNA does not double Chromosomes randomly line-up along metaphase plate like regular mitosis. During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell. Nuclei reform and cytokenesis usually occurs (although it is often unequal).

32. Overview of Meiosis

33. Comparison of Mitosis & Meiosis