Cell Division: The Process of Mitosis

1. Cell Division: The Process of Mitosis

2. Important terms in eukaryotic cell division • Chromosome = threadlike structures that are composed of DNA + protein • replication = process whereby DNA is identically copied (before cell division) • mitosis = division of the nucleus • cytokinesis = division of the cytoplasm • chromatin = DNA + protein complex that is thin and fibrous; it will condense into distinct chromosomes during cell division

3. one of the major characteristics of living things is the ability to GROW • an adult doesn't have bigger cells, they have more cells You can grow too many cells!!!

4. When do cells divide? • Reproduction • Replacement of damaged cells • Growth of new cells • In replacement and growth cell divisions how should daughter cells compare to parent cell? • The daughter cells should be identical copies of the parent cell.

5. 3 main stages of the cell cycle: • Interphase: longest stage; preparation for cell division • Mitosis: nucleus divides into 2 nuclei, each with the same # and kind of chromosomes (DNA) as the parent cell • Cytokinesis: cytoplasm divides forming 2 distinct cells

6. Cell Cycle Overview • Interphase: quite long (most of the cell’s time spent here) • Cell Division: occurs quickly

7. Interphase • 90% of cell cycle is spent in this phase • G1 = first growth phase • S = synthesis phase, DNA synthesis (replication) occurs here • G2 = second growth phase; centrioles are replicated.

8. Why is it important that the nucleus divides in mitosis? • it stores the DNA (information of life) • all new cells need this information

9. Chromosomes • Genetic information is passed on from one generation to the next through chromosomes • Every organism has a specific number of chromosomes (ex: humans = 46, carrots = 18) • Chromosomes are not visible in most cells except in cell division

10. DNA and protein molecules that make up chromosomes is spread through the nucleus • At the beginning of cell division, the chromosomes condense into compact visible structures (chromosomes) • Before cell division, each chromosome is replicated (copied) • Each chromosome is made up of 2 identical “sister” chromatids held together by a centromere

11. chromosome centromere chromatin DNA

12. Mitosis is one, continuous event, but it can be described as happening in 4 phases: • Prophase • Metaphase • Anaphase • Telophase

13. **Remember, the cell is coming out of Interphase…

14. PROPHASE In the Nucleus: • Nucleoli disappear • Chromosome fibers condense into discrete chromosomes • Each chromosome consists of 2 sister chromatids joined at the centromere

15. PROPHASE continued… • In the Cytoplasm: • mitotic spindle begins to form • spindle consists of microtubules arranged between the centrioles • centrioles move apart due to lengthening of microtubules

16. PROPHASE

17. METAPHASE A.) chromosomes line up in the center of the cell; B.) spindle fibers connect from the poles (end) of the spindle to the centromere of each chromosome

18. METAPHASE

19. ANAPHASE A.) centromeres split, causing the sister chromatids to separate, becoming individual chromosomes B.) chromosomes are pulled apart to opposite ends of the cell (the shape of the cell elongates into an elipse)

20. ANAPHASE

21. TELOPHASE A.) chromosomes uncoil into chromatin B.) new nuclear envelope forms around the chromatin C.) spindle breaks apart D.) nucleolus reappears in each new nucleus

22. TELOPHASE

23. Finally… CYTOKINESIS animal cells: cell membrane pinches in & divides (cleavage furrow) plant cells: a cell plate forms (new cell wall) **Begins before telophase has completed**