1. Ch. 10 Cell Growth and Division

2. Chapter 10 Outline 10-1: Cell Growth –Limits to Cell Growth –Division of the Cell 10-2: Cell Division –Chromosomes –The Cell Cycle –Events of the Cell Cycle –Mitosis –Cytokinesis 10-3: Regulating the Cell cycle –Controls on Cell Division –Cell Cycle Regulators

3. Limits to Cell Growth There are two main reasons why cells divide instead of grow indefinitely: 1.The larger a cell becomes the more demands it places on the DNA 2.The Cell has more trouble moving enough nutrients and wastes across the cell membrane There is only a finite amount of DNA in a cell. If a cell grows larger, that same amount of DNA has to support the entire cell

4. Limits to Cell Growth The rate at which nutrients, water and wastes move across the cell membrane depends on the surface area of the cell membrane. As a cell grows larger, its volume increases more than the surface area, therefore, there isn’t enough surface area (of plasma membrane) to support the whole cell.

5. Cell Size Table Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume

6. Division of the Cell Before it becomes too large, a growing cell will divide forming two “daughter” cells. This process is called Cell Division. Before cell division occurs, the cell replicates (copies) its DNA so that each of the two daughter cells will have a full set of DNA.

7. Cell Division In prokaryotes, cell division is called binary fission. Bacterial DNA is circular. The DNA is copied and the cell splits in two. In eukaryotes, much more preparation is required because of the presence of many pieces of DNA –Two main stages of eukaryotic cell division: Mitosis – division of the nucleus Cytokinesis – Division of the cytoplasm

8. Cell Division (con’t) Mitosis is a type of asexual reproduction since cells are genetically identical to the parent cell.

9. Chromosomes In eukaryotic cells, genetic information is passed on from parent cells to daughter cells in the form of chromosomes. Chromosomes are made up of DNA (which carries the genetic code) and proteins. Every organism has a unique number of chromosomes. Humans have 46 chromosomes or 23 pairs.

10. Chromosomes (con’t) Chromosomes only form during cell division. DNA normally exists in the cells in a long, stringy form called chromatin. When it is time for a cell to begin division, the chromatin condenses and forms tightly packed Chromosomes. Just before cell division, the DNA must copy itself (so that each daughter cell gets a full set of DNA).

11. Chromosome (con’t) Each side of a chromosome that has already replicated is called a sister chromatid. Sister chromatids are identical. When a cell divides, sister chromatids separate from each other. Sister chromatids are attached to each other in an area called the centromere.

12. The Cell Cycle 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 two daughter cells. –The Two daughter cells then begin the cycle again.

13. Cell Cycle (con’t) Phases of the Cell Cycle –M phase Mitosis Cytokinesis –Interphase G 1 phase S phase G 2 phase

14. Events of the Cell Cycle Which phase is longer? –Interphase is very long, but mitosis and cytokinesis take place quickly. –G 1 phase: Cells are growing, making new proteins and organelles –S (synthesis) phase: Chromosomes are replicated –G 2 phase: More growth, more organelles made to prepare for cell division

15. Mitosis Mitosis is divided into four phases: –Prophase –Metaphase –Anaphase –Telophase Prophase: longest phase –Chromosomes form –Centrioles separate (centrioles lie near the nuclear envelope and help organize the fanlike structure called the spindle which help separate the chromosomes) –Chromosomes attach to fibers in spindle –Nucleolus and nuclear envelope disappear

16. Mitosis (con’t) Metaphase –Chromosomes line up at the equator or middle of the cell Anaphase –Sister chromatids separate and become individual chromosomes –Chromosomes move to opposite sides of the cell

17. Mitosis (con’t) Telophase –Chromosomes unwind –Nuclear envelope reforms around each set of chromosomes –Spindle breaks apart –Nucleolus reappears After the NUCLEAR division is complete, the cell still must divide.

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

19. 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

20. 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

21. 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

22. 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

23. 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

24. Cytokinesis The process of cytoplasm dividing can happen in two ways : –Animal cells: cell membrane is drawn inward (cleavage furrow ) until the cytoplasm is pinched into two parts –Plant cells: cell plate forms midway between the divided nuclei. The cell plate gradually develops into a separating membrane and a cell wall forms there.

25. THE CELL CYCLE M phase G 2 phase S phase G 1 phase

26. Controls on Cell Division Cells stop growing when they come in contact with other cells –Ex: If you put some cells on a Petri dish with nutrient broth in it, they will divide until they cover the whole Petri dish.

27. Cell Cycle Regulators For many years, scientists searched for a substance that regulates the cell cycle. In 1980, that substance was identified and named cyclin. –Cyclin is a protein that regulates the timing of the cell cycle in eukaryotic cells Many other proteins have since been discovered that help regulate the cycle.

28. A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G 2 of interphase. As a result, the second cell enters mitosis. Effects of Cyclin

29. Cell Cycle Regulators Two types of regulatory proteins: 1.Internal regulators: –Respond to events inside the cell –Allow the cell cycle to proceed only after certain processes happen inside the cell 2.External regulators: –Respond to events outside the cell –Direct cells to speed up or slow down the cycle –Ex. Growth Factors

30. Uncontrolled Cell Growth Cancer: –A disorder in which some of the body’s own cells lose the ability to control growth –Cancer cells do not respond to the signals that regulate growth of most cells –They form masses of cells called tumors. Cells in tumors can break free and spread throughout the body. Causes of Cancer –Smoking –Radiation exposure –Viral infection