1. The Need for Cell Division During development – One fertilized egg cell begins to divide – Develops into a mature multicellular organism In adults – To repair damage – To replace worn out tissue

2. Stages of the Cell Cycle Before a cell can divide: – Key cellular components must be duplicated Proteins, membranes, and organelles –Chromosomes must be duplicated Complete set of genetic information –Ensures that the new cells can survive

3. The Cell Cycle (eukaryotes): Mitosis Interphase cytokinesis

4. Interphase has 3 phases: G1 Phase or Gap 1: Longest phase Cell growth, Proteins/lipids synthesized, Prepares for replicating DNA G1 Start after cell division

5. Interphase: S Phase G1 S DNA Synthesis (Chromosomes/ chromatin Replicated)

6. Interphase: G2 Phase G1 S G2 Prepares for cell division, proteins made Mitochondria replicate Centrioles replicate Microtubule synthesis

7. Mitosis: Nuclear division Microtubules separate chromosomes G1 S G2 Mitosis

8. Cytokinesis: Cell division, divides into 2 daughter cells Cell may renter cell cycle Or leave cell cycle (G0) G1 S G2 Mitosis Cytokinesis G0

9. G 0 Phase Most cells are not actively dividing These cells are in G 0 phase –Can leave cell cycle for days to years – Some cells will divide again; e.g. liver cells – Some cells stay in G 0 ; e.g. nerve cells

10. Interphase – G1, S, & G2 Phases

11. MITOTIC PHASES Prophase Metaphase Anaphase Telophase

12. Mitosis: Prophase

13. Mitosis: Metaphase 1.Microtubules grow, connect to centromeres, 2.and align the chromosomes

14. Mitosis: Anaphase 1.Sister chromatids separate, move to opposite poles. 2.Microtubules shorten & pull them in.

15. Mitosis: Telophase 4 1.Chromosomes at poles 2.Nucleus reforms 3.Chromosomes unwind into chromatin 4.Spindle degrades

16. Cytokinesis 1.Cytokinesis follows mitosis. 2.In animal cells, actin filaments (protein) pinch the cell in two. 3.Seen as a cleavage furrow on the cell membrane. 4.Plant cells divide by growing a new cell wall (cell plate) between the 2 nuclei.

17. DNA Synthesis Occurs in S-phase of interphase DNA Synthesis & Chromosomal Replication:

18. Chromosomes

19. Mitosis Review Allows for: –Growth –Replacement of cells –Asexual Reproduction Identical Cells Video of a cell dividingVideo