1. Cell Growth & Division Mitosis

2. Cell Growth Cell Growth is limited because: The larger a cell becomes, the more demands the cell places on its DNA. The larger a cell becomes, the more trouble the cell has moving enough nutrients and wastes across the cell membrane.

3. DNA Overload As a cell increases in size, it usually does not make extra copies of its DNA. If a cell grows too large, it will have an “information” crisis – the DNA could not provide enough information to meet all of the needs of the cell.

4. Exchanging Materials It is more difficult for a large cell to get oxygen and nutrients in and waste products out.

5. Cell Division The process by which a cell divides into new daughter cells. Before a cell divides, it first replicates or makes a copy of its DNA This replication of DNA insures that each new daughter cell will have a complete copy of DNA.

6. Two Types of Cell Division Mitosis – occurs in the autosomes – the body cells (somatic cells); does not occur in the reproductive cells; Meiosis – occurs in the reproductive cells – the egg and the sperm cells; does not occur in the autosomes;

7. Cell Division - Prokaryotes Binary Fission – occurs in bacteria. DNA is replicated, then the process of cell division is a simple matter of separating the contents of the cell into two new bacterial cells. Cell division in prokaryotes occurs exponentially – the population doubles in a very short time.

8. Chromosomes Carries the genetic information that is passed from one generation of cells to the next generation. Made up of DNA which carries the cell’s coded genetic information and proteins. The cells of every organism have a specific number of chromosomes. Human cells have 46 chromosomes (diploid number)

9. Chromosomes Chromosomes are only visible during cell division when They condense into compact, visible structures After replication, chromosomes consist of two identical “sister” chromatids.

11. Chromosomes Each pair of chromatids is attached near the middle of the chromosome in an area called the centromere. A human body cell entering cell division contains 46 chromosomes each consisting of two chromatids.

12. Cell Cycle The series of events that cells go through as they grow and divide. During the cell cycle, a cell grows, prepares for division and divides to form new daughter cells each of which begins the cell cycle again.

13. M phase G 2 phase S phase G 1 phase Figure 10–4 The Cell Cycle Section 10-2 Go to Section:

14. The Cell Cycle G1 phase – Period of activity in which cells do most of their growing. Cells increase in size and synthesize (make) new proteins and organelles. S phase – Chromosomes are replicated and the synthesis of DNA molecules take place.

15. Cell Cycle G2 phase – Many of the organelles and molecules required for cell division are produced. G1, S & G2 phases are known as Interphase. M phase – Mitosis or the division of the cell nucleus.

16. Mitosis – The Division of the Cell Nucleus Divided into 4 phases: Prophase Metaphase Anaphase Telophase

17. CELL DIVISION ORGANELLES Centrioles-two tiny structures in the cytoplasm near the nuclear membrane on each end; Centrioles help to organize the spindle fibers.

18. CELL DIVISION ORGANELLES Spindle Fibers – fanlike, microtubule structures that help separate the chromosomes.

19. Prophase Events The longest phase of mitosis Chromosomes become visible Centrioles appear and move to the ends of the cell (on each side of the nucleus) The condensed chromosomes become attached to the spindle fibers near the centromere. Nucleolus & nuclear membrane disappear.

20. Metaphase Events Lasts only a few minutes. Chromosomes (two sister chromatids) line up across the middle of the cell.

21. Metaphase

22. Anaphase Events Centromeres separate. Sister chromatids separate and become individual chromosomes. Chromosomes move away from the middle of the cell to the ends.

24. Telophase Events Chromosomes begin to form back into chromatin. Nuclear membrane reforms around each cluster of chromosomes. Spindle fibers break down Nucleolus becomes visible in each daughter cell

26. Cytokinesis As a result of mitosis, two nuclei are formed within the cytoplasm of one cell. Cytokinesis is the division of the cytoplasm and occurs at the same time as telophase.

27. Animal Cell Cytokinesis

28. Plant Cell Cytokinesis – cell plate

29. The Product of Mitosis Mitosis produces TWO NEW DAUGHTER CELLS IDENTICAL to the parent cell; Each new daughter cell has the diploid number of chromosomes;