Cell Growth and Division

1. Cell Growth and Division Chapter 10

2. Why do cells divide? • As the cell grows the DNA has an increased work load. As the cell gets bigger the DNA has to work harder to control the cell • As the cell grows the exchange of materials through the cell membrane becomes limited • When one of these two conditions are met (or both) the cell must divide

3. Surface area to volume • If a cell gets to be too large it would be too hard for the cell to get enough oxygen and other nutrients in and waste products out. • The volume of a cell increases faster than the surface area of the cell. When this incerease happens the cell faces some problems.

4. Problem solved • The process by which a cell divides into two new daughter cells is cell division • New DNA allows for easier information storage • Cell division reduces cell volume • This allows better exchange of materials

5. Cell division • Complex cell division occurs in eukaryotic cells • 2 stages • Mitosis-asexual division of the nucleus • Cytokinesis-division of the cytoplasm

6. Chromosomes • Are made up of DNA • DNA carries the cell’s genetic information • Humans have 46 chromosomes • Chromosomes are only visible during cell division • Before cell division each chromosome is replicated

7. Chromatids • Each chromosomes consists of two identical sisters known as chromatids • When the cell divides they separate from each other • They are attached at the center by as centromere

9. The cell cycle • interphase- • In between stage, period of growth • During the cell cycle • Cell grows • Prepares for division • Divides to form 2 daughter cells • 2 daughter cells begin the cycle again

11. 4 phases of the cell cycle • Mitosis and cytokinesis take place during the M phase • Cell growth occurs during the G1 phase • DNA replication occurs during the S phase • Preparation for mitosis begins during the G2 phase

12. Mitosis • Consists of 4 phases • Prophase • Metaphase • Anaphase • Telophase

13. Prophase • Chromosomes pair up • First and longest phase • Centrioles appear, separate, and move to opposite sides of the nucleus • Organize the spindle, which helps separate the chromosomes, and attach to the fibers in the spindle • Nucleolus disappears, nuclear envelope breaks down

15. Metaphase • Chromosomes line up in the middle of the cell • Each chromosome is connected to a spindle fiber at its centromere • Only lasts a few minutes

17. Anaphase • Chromosomes get pull Apart • Centromeres split allowing the sister chromatids to separate and become individual chromosomes • Chromosomes move into two groups near the poles of the spindle • This phase ends when the chromosomes quit moving

19. Telophase • Final stage • Chromosomes tangle into dense material • Nuclear envelope reforms around the cluster of chromosomes • Spindle breaks apart, nucleolus becomes visible in each new daughter cells (2) • Mitosis is not complete yet, cell division is though

21. Cytokinesis • Two new nuclei are formed within the cytoplasm of a single cell • Occurs at the same time as telophase • Cell membrane is pinched off into two equal parts • Each part contains its own nucleus and cytoplasmic organelles.

24. Points to Remember • After mitosis and cytokinesis you end up with 2 identical daughter cells • Original cell is diploid (2n) and the 2 daughter cells are also diploid (2n) • Original cell divides one time