1. CHAPTER 10 CELL GROWTH AND DIVISION
A. Limits to Cell Growth
1. DNA overload
- when cells increase in size, they place greater demands on the DNA (which does not increase in size) and the DNA cannot meet the cell’s needs

2. 2. exchanging materials - moving of nutrients and wastes across the cell membrane becomes more difficult and depends on the total surface area of the cell membrane as well as the amount of nutrients and wastes that must be moved (volume) 3. ratio of surface area to volume - the key to understanding why cells must divide as they grow - volume of cells increase more rapidly than surface area, causing ratio of surface area to volume to decrease causing serious problems for cells - it is more difficult to get oxygen and nutrients in and waste products out

3. Ratio of surface area to volume

4. 4. cell division - the process by which cells divide before they become too large, forming 2 daughter cells - prior to division, the cell makes a copy of its DNA (replication) - each daughter cell will get one complete set of genetic information - cell division reduces cell volume and each daughter cell has an increased ratio of surface area to volume allowing materials to be exchanged with the environment more efficiently

5. 10-2 Cell Division - all cells must prepare to divide by making copies of their DNA - prokaryotes can then simply separate into two, whereas with eukaryote cells, it is a more complex process

6. A. Chromosomes - carry the genetic information that is passed from one generation to the next - made up of DNA and proteins - the cells of every organism have a specific number of chromosomes Ex. fruit flies; 8 humans; 46 carrot cells; 18 - chromosomes are visible only during cell division - in a resting cell, they are spread out within the nucleus and condense into compact, coiled structures at the beginning of cell division - because they have been copied by the time they are visible, each chromosome appears as two identical or “sister” chromatids - each chromatid is attached in an area called the centromere usually located at the center of the chromatids

7. Chromosome

8. B. The Cell Cycle - represents the recurring series of events that take place in the life of a cell - during the cell cycle, these events include: • growth • preparation for division • division into two daughter cells - consists of 4 phases 1. G1 – growth phase 2. S – copying of DNA (replication) 3. G2 – preparation for mitosis 4. M – mitosis occurs, division of nucleus, and cytokinesis Interphase – the period in the cycle when the cell is not dividing but is growing and includes G1, S, and G2

9. C. The Events of the Cell Cycle Interphase - can be long - consists of G1, S, and G2 G1 phase - the period when the cells are actively growing - cells increase in size and make new proteins and organelles S phase - follows G1 - chromosomes are replicated and DNA is synthesized as well as proteins associated with DNA - once a cell enters the S phase, it completes the entire cycle including mitosis G2 phase - begins when DNA replication is completed - shortest phase in interphase - organelles, including centrioles, and proteins needed for cell division are produced - when G2 is complete, cells begin mitosis

10. Cell cycle

11. D. Mitosis - divided into four phases which can last from a few minutes to many days depending on the type of cell. 1. Prophase - first and longest phase (50-60% of time of mitosis is spent in prophase) - chromosomes become visible as chromatin condenses - centrioles separate and move to opposite sides of the nucleus and a spindle begins to form ****plant cells do not have centrioles - chromosomes attach to spindles at a point near the centromere of each chromatid - nuclear membrane breaks down; nucleolus disappears

12. 2. Metaphase (few minutes) - the chromosomes line up across the center of the cell - each chromosome is connected to a spindle fiber at its centromere 3. Anaphase - the centromeres joining sister chromatids split and the chromatids separate and become individual chromosomes which move to opposite sides of the cell

13. 4. telophase - chromosomes lose their coiled shape - nuclear membrane reforms around each set of chromosomes - spindle fibers break down - nucleolus becomes visible - mitosis is complete E. Cytokinesis - division of the cytoplasm - occurs at the same time as telophase - cytoplasm pinches in half - in plants, a cell plate forms between the divided nuclei which will gradually develop into a cell wall

14. Mitosis

15. 10-3 Regulating the Cell Cycle A
10-3 Regulating the Cell Cycle A. Controls on Cell Division - controls over cell growth and cell division can be turned on and off - when cells come into contact with other cells, they stop growing - cells near the site of an injury will divide rapidly until healing is almost complete, and then the rate of cell division decreases returning cell growth to normal

17. B. Cell Cycle Regulators (what turns cells on and off) - a group of related proteins called cyclins regulate the timing of the cell cycle in eukaryotic cells There are two types of regulatory proteins: 1. Internal regulators - proteins that respond to events inside the cell a. they make sure cells do not enter mitosis until replication is complete b. prevent a cell from entering anaphase until all chromosomes are attached to mitotic spindles

18. 2. External regulators - proteins that respond to events outside the cell a. direct cells to speed up or slow down the cell cycle b. act as growth factors that stimulate growth and division of cells during embryonic development and wound healing c. may be found on cell surfaces and would prevent excessive cell growth by stopping or slowing down the cell cycle

19. C. Uncontrolled Cell Growth (cancer) - careful regulation of cell growth will prevent uncontrolled cell growth preventing serious consequences like we see with cancer cancer cells - do not respond to signals that regulate the growth of most cells resulting in tumors that damage surrounding tissues - cancer is a disease of the cell cycle

21. What causes loss of growth control
What causes loss of growth control? - some cancer cells do not respond to external growth regulators - some do not produce internal regulators that ensure orderly growth - some cancer cells have a defect in a gene called p53 which would stop the cell cycle until replication is complete and cells do not respond to controls that regulate growth