1. The Cell Cycle A mechanism for cell growth and division

2. Why Do Cells Divide? Growth and repair of tissue in multi-cellular organisms/Eukaryotes. Method of reproduction for single celled organisms/Prokaryotes (binary fission). Also important in the specialization of cells into tissue and organs. Keeps cell size small (very important).

3. Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume Ratio of Surface Area to Volume in Cells Section 10-1

4. Why Are Cells Small? MOST CELLS ARE SMALL FOR TWO REASONS: 1. A SMALL CELL HAS MORE SURFACE AREA THAN A LARGE CELL FOR A GIVEN VOLUME OF CYTOPLASM and can absorb more nutrients more efficiently/quickly. 2. THE CELL'S NUCLEUS (THE BRAIN) CAN ONLY CONTROL A CERTAIN AMOUNT OF LIVING, ACTIVE CYTOPLASM therefore large cells would require enormous amounts of DNA in order to function properly.

5. Overview of The Cell Cycle The Cell Cycle is divided into 4 stages: –G1-phase –S-phase –G2-phase - M phase Cytokinesis The Cell cycle is an endless repetition of mitosis, cytokinesis, growth, DNA replication Interphase- period of time between divisions and includes G1-phase period of initial growth S-phase “synthesis” DNA is being replicated G2-phase Second period of growth and preparation for division M-phase =“mitosis” is the division of the nucleusM-phase Cytokinesis division of the cytoplasm and organelles Cell Division

6. Interphase The longest part of the cell life cycle Divided into three distinct stages: G1 or Gap 1 phase- initial growth of newly formed cell, organelles duplicated, protein production Cells increases in mass and volume, organelles are replicated Dna exists as uncoiled Chromatin S or Synthesis Phase- DNA and chromosomal protein replication (chromosome doubled) *Chromosomes are not visible, exists as chromatin (uncoiled DNA) G2 or Gap 2 Phase- growth after DNA replicates, cell prepares itself for division making proteins needed to form the spindle fibers which will move the chromosomes in mitosis.

7. Chromosomes DNA in Eukaryotic cells is condensed and packaged into units called chromosomes Humans have 46 Each Chromosome consist of two DNA molecules. Copies where made in DNA replication(S-phase) Because these two Dna molecules are exact, Each copy is called a Sister Chromatid Centromere gene

8. Section 10-2 Mitosis and Cytokinesis Mitosis is nuclear division of cells process where cells divide, sort, and package, genetic material (DNA) prior to cell division.Mitosis Divided into four distinct stages –Prophase –Metaphase –Anaphase –Telophase Cell Division involves mitosis and the separation of the cytoplasm and organelles in CytokinesisCytokinesis

9. Overview of The Cell Cycle Interphase –G1-phase –S-phase –G2-phase M phase “Mitosis” ( Division of the nucleus and separation of genetic material ) Divided into: Prophase, Metaphase, Anaphase,Telophase. Cytokinesis –Actual division of the cell and cytoplasm into two daughter cells G 1 phase S phase G 2 phase Cell Division

10. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming Section 10-2 Figure 10–5 Mitosis and Cytokinesis

11. Prophase Chromosomes condense/coil and become more visible Centrioles move towards opposite poles Nuclear membrane breaks down and disappears Centrioles are now at opposite poles of the nucleus Spindle fibers extend from the centrioles at the poles to the centromeres on the chromatids Prometaphase

12. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming Section 10-2 Figure 10–5 Mitosis and Cytokinesis

13. Metaphase Chromosomes line up at the equatorial plane of the cell Spindle fibers are attached to the centromere of each chromatid

14. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming Section 10-2 Figure 10–5 Mitosis and Cytokinesis

15. Anaphase Begins when the spindle fibers start pulling the sister chromatids toward the poles. Kineticore (centromeres) detach/break and spindles drag each sister chromatid to the poles.

16. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming Section 10-2 Figure 10–5 Mitosis and Cytokinesis

17. Telophase Final phase of mitosis Chromosomes decondense Nuclear membrane begins to reform around each set of chromosomes Spindle fibers begin to break down Cell membrane begins pinching or cleaving

18. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming Section 10-2 Figure 10–5 Mitosis and Cytokinesis

19. Cytokinesis Last stage of the cell cycle, also the shortest in terms of time Separation of the cytoplasm and organelles Cytokinesis in plant and animal cells differs -animal cells divide by pinching from the outside towards the inside forming an indentation known as a cleavage furrow -plants divide from the inside towards the outside by forming small membranous vesicles known as a cell plate(c)

20. Summary of Mitosis -a form of cell division that produces two daughter cells, each having the same genetic content as the parent cell. Parent cell 46 chromosomes  2 daughter cells 46 chromosomes -Produces diploid cells- having 2 copies of each chromosome (2n). -Chromosomes are made up of identical chromatids (sister chromatids) -Chromatids are separated and then segregated to different daughter cells. -Produces two daughter cells (genetic clones) - occurs in the somatic cells (body cells) forming muscle, epithelial (skin), nervous, and connective tissues

21. How is the Cell Cycle Controlled? Genes (segments of DNA) instruct the cell to produce certain proteins and enzymes. Genes are like light switches, can be turned on/off Genes contain protein units of information (cyclins) that instruct the cell in division and act as internal regulators of cell division External regulators also regulate growth Contact inhibition-cell to cell communication between the plasma membranes of side by side cells

22. What if the Cell Cycle goes Out of Control? Mistakes in the internal regulation of the cell cycle is known as CANCERCANCER Uncontrolled division of cells results from an overproduction of cyclin proteins by genes External factors can also influence genes and ultimately cell division Mutagenic agents- nicotine,UV light, PCB’s