2. 2.5 Cell Division How you got from one to trillions!!

3. Conception All animals begin as a fertilised egg cell (a zygote) Image Credit: ZygoteZygote

4. Then it divides… Image Credit: www.ehd.org/www.ehd.org/

5. … and divides Released into the Public Domain by JrockleyJrockley

6. Until it becomes an embryo Image Credit: www.scienceclarified.comwww.scienceclarified.com

7. Cell Cycle Interphase Longest phase (94%) G1: Cell growth S: Replication of DNA G2: Growth for division of cell Mitosis Division of nucleus and chromosomes Cytokinesis Division of cytoplasm and organelles into two daughter cells. 2.5.1

8. Cell cycles are not uniform Cell typeCell cycle / h Bean root tip19.3 Mouse fibroblast22 Chinese hamster fibroblast11 Mouse small intestine epithelium 17 Mouse esophagus epithelium181 © 2010 Paul Billiet ODWSODWS

9. Mitosis Cell Basics Somatic (body) cells. Diploid (2n): one chromosome from each parent. (n=23) Duplicated chromosomes have 2 sister chromatids. Attached at centromere in the middle. Both are called chromosomes!!

10. Mitosis Responsible for cellular: Growth Embryonic development Tissue repair Asexual Reproduction 2.5.6

11. Interphase Active period. Many metabolic reactions occur, including protein synthesis. Increase in number of mitochondria and/or chloroplasts. Most important: DNA replication while chromatin. S phase. 2.5.3

12. Interphase

13. Prophase Preparing. Supercoiling of chromosomes (condense) Nuclear membrane and nucleolus disappear. 2.5.4

14. Prophase

15. Metaphase Meet in the Middle. Attachment of spindle microtubules to centromeres, one from each centriole. All chromosomes are lined up at the middle, also called the equator. Equal pulling from opposite ends. 2.5.4

16. Metaphase

17. Anaphase Moving away Centromeres split. Sister chromatids are pulled to opposite poles by spindle fibers. Each is now considered a chromosome. Two diploid cells are forming. 2.5.4

18. Anaphase

19. Telophase Two nuclei. Chromosomes change to chromatin. Nuclear membrane reforms. New nucleoli form. Cytokinesis is usually happening at the same time as telophase. 2.5.4

20. Telophase

21. Cytokinesis Cell membrane and cytoplasm division. Two genetically identical nuclei now found in two diploid daughter cells. 2.5.5