1. Cell Growth and Division How would you describe the process by which a multicellular organism increases its size? Why do cells stay small?

2. Objectives • Explain the problems that growth causes for cells. • Describe how cell division solves the problems of cell growth.

3. Limits to Cell Growth • The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cellmembrane. • Two reasons why cell size is limited: • If a cell were to grow without control, DNAoverload would occur. • Rate of material exchange is dependent on surfacearea http://www.youtube.com/watch?v=xuG4ZZ1GbzI

4. Exchanging Materials • Food, oxygen and water enter the cell through the cellmembrane. Waste products leave the same way. • The rate at which this exchange takes place depends on surfacearea (the total area of its cell membrane)

5. Cell Division • Before a cell becomes too large, it divides into two daughtercells by a process called celldivision.

6. What are Chromosomes? • Chromosomes are made up of DNA • DNA carries the cell’s geneticcode • The cells of every organism have a specificnumber of chromosomes.

7. Uncoiled DNA

8. DNA Coils into Chromosomes

9. The structure of a chromosome • Chromatin • Chromatid • Centromere • Chromosomes are notvisible in most cells except during celldivision. • At the beginning of cell division the chromosomes condense into compact, visible structures that can be seen under a light microscope.

10. The Chromosome • Chromosome: “X” shaped cell structure that directs cell activities and passes on traits to new cells. • Each identical strand of the chromosome is called a chromatid. • The strands are heldtogether by a structure called the centromere. • Chromatin: Loosely coiled DNA

11. Parts of a Chromosome

12. The Cell Cycle • Interphase • G1 Phase: Cell Growth • S Phase: DNA Replication • G2 Phase: Preparation for Mitosis • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis M Phase

13. The Phases • Interphase • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis I Promised My Aunt Tina Chocolate

14. Links http://www.cellsalive.com/mitosis.htm http://www.cellsalive.com/cell_cycle.htm

15. Interphase: G1 • Cell Grows • Synthesis of proteins and new organelles

16. S-Phase • Chromosomes are duplicated and the synthesis of DNA molecules takes place.

17. G2 Phase • Many of the organelles and molecules required for cell division are produced. • The cell is then ready to enter M-Phase to begin the process of Cell division

18. Prophase • The chromatin condense into chromosomes. • The centrioles separate and a spindle begins to form. • The nuclear membrane breaks down.

19. Metaphase • The chromosomes line up along the middle of the cell. • “M”eet in the “M”iddle! • Each chromosome is connected to a spindle fiber at its centromere.

20. Anaphase • The sister chromatids separate into individual chromosomes and move apart. • Anaphase pulled Apart

21. Telophase • The chromosomes gather at opposite ends of the cell and lose their distinct shapes. • Two new nuclear membranes form • Two new Nuclei

22. Cytokinesis • The cell membrane pinches the cytoplasm in half. • Each daughter cell has an identical set of duplicate chromosomes.

23. Plant Cells • Plant cells have a cell plate that forms between the two cells. • The cellwall is too rigid to be pinched apart.

24. Length of the Cell Cycle of a Human Liver Cell • Interphase: 21 hours • Growth : 9 hours • DNA Replication: 10 hours • Preparation for Division: 2 hours • Mitosis: 1 hour • Prophase • Metaphase • Anaphase • Telophase

26. Uncontrolled Cell Growth • Cancer- a disorder in which some of the body’s own cells lose the ability to control growth. • Disease of the cell cycle

27. Summary Video