Chapter 10 Notes Cell Growth and Division

A.Limits to Cell Growth ~ Two main reasons why cells divide rather than grow indefinitely is: –1. DNA “Overload” ~ explain –2. Exchanging Material ~ explain 10–1 Cell Growth pg. 241 If a cell grows too large, an information crisis would occur. The cell’s DNA would no longer be able to serve the increasing needs of the growing cell. The rate at which the exchange of nutrients and waste depends On the surface area of the cell, which is the total areas of its cell membrane. However, the rate at which nutrients are used and waste products are produced depends on the cell’s volume. If the cell is too large, too difficult to make the exchanges.

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 The volume increases much more rapidly than the surface area, causing the ratio of surface area to volume to decrease. This decrease causes serious problems for the cell. If the cell got too large, it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste out.

Division of the Cell ~ why does division occur & what occurs? First the cell must copy its genetic information for each daughter cell to have a copy ~ mitosis. Then the cell separates the contents of the cell into two parts ~ cytokinesis. Division must occur in cells in order for prokaryotic & one celled organisms to reproduce and in order to develop the various parts of eukaryotic organisms.

A. Chromosomes ~ Made of? Visible? Replication? Draw diagram Cell Division pg. 244 Made of DNA ~ which carries the cell’s coded genetic information and proteins. Chromosomes are not visible in most cells except during cell division. Usually the chromosomes are spread throughout the nucleus, but condense a the beginning of cell division. Replication is to copy a chromosome. Because of this, each chromosome consists of two sister chromatids. As the cell divides, the sister chromatids separate from each other and one chromatid goes to each of the new cells.

Chromosome Diagrams

c. Cell Cycle ~ definition, phases are… & what happens in each? M phase – mitosis (cell division) During the cell cycle, the cell grows, prepares for division & divides to form two daughter cells. G1 phase – cells increase in size and synthesize new proteins & organelles. S phase – chromosomes are replicated and the synthesis of DNA molecules takes place. G2 phase – the shortest phase; many of the organelles & molecules required for cell division are produced.

M phase G 2 phase S phase G 1 phase Figure 10–4 The Cell Cycle

The cell cycle represents recurring events that take place in the period of time from the beginning of one cell division to the beginning of the next. In addition to cell division, the cell cycle includes periods when the cell is growing and actively producing materials it needs for the next division. 1.Why is the cell cycle called a cycle? 2.Why do you think that it is important for a cell to grow in size during its cell cycle? 3. What might happen to a cell if all events leading up to cell division took place as they should, but the cell did not divide? Some might infer that a cell that undergoes all sequences of the cell cycle would grow increasingly larger—to a point at which the cell could no longer exchange materials with the environment efficiently enough to live. It represents recurring events. If a cell did not grow in size, each cell division would produce progressively smaller cells.

E. Mitosis pg. 246 ~ four phases are…& what happens? Animal Cell Mitosis Prophase ~ the first and longest phase when the chromosomes become visible. Centrioles take up positions on opposite sides of the nucleus. The spindle fibers attach to centromere, the nucleolus disappears, and the nuclear envelope breaks down. Metaphase ~ often lasts only a few minutes. The chromosomes line up across the center of the cell. Microtubules connect the centromere to the poles of the spindle fibers. Anaphase ~ The centromeres of the sister chromatids split and the chromatids separate to become individual chromosomes. The chromosomes move untill they separate into two groups near the poles of the spindle. Telophase ~ The chromosomes begin to disperse into a tangle of dense material. The nuclear envelope reforms.

F. Cytokinesis pg. 248 ~ definition & what happens? cytokinesis Cytokinesis is the division of the cytoplasm & usually occurs at the same time as telophase. In animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. In plant cells, a cell plate forms midway between the divided nuclei and gradually develops into a separating membrane. A cell wall then begins to appear.

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

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

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

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

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

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

includes is divided into Concept Map Cell Cycle M phase (Mitosis) Interphase G 1 phaseS phaseProphaseG 2 phaseMetaphaseTelophaseAnaphase

Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new. 1.How do you think the body repairs an injury, such as a cut on a finger? 2.How long do you think this repair process continues? 3.What do you think causes the cells to stop the repair process? When the cut is filled in, there is no room for more cells to grow. The cut is repaired by the production of new cells through cell division. Cell division continues until the cut is repaired.

10–3 Regulating the Cell Cycle pg. 250 A. Controls on Cell Division ~ what controls & how tested? Contact of other cells stops growth. Cells were place in a petri dish to find that when the cells contact other cells, the growth stops.

Control of Cell Division

1. 2. B.Cell Cycle Regulators ~ what regulates, who discovered? Cyclin, a protein, regulates the timing of the cell cycle in eukaryotic cells. Tim Hunt of Great Britain & Mark Kirschner of the US performed experiments with cells in mitosis.

Figure 10–8 Effect of Cyclins 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.

a.Internal Regulators ~ definition & examples b.External Regulators ~ definition & examples ~Proteins that respond to events inside the cell are called internal regulators. ~Several internal regulators make sure that a cell does not enter mitosis until all its chromosomes have been replicated. ~Another regulatory protein prevents cells from entering anaphase until all the chromosomes are attached to the mitotic spindle. ~Proteins that respond to events outside the cell are called external regulators. They direct cells to speed up or slow down the cell cycle. Growth factors are the most important. ~Embryonic development & wound healing are examples.

Uncontrolled Cell Growth pg. 252 Reasons for growth, causes of loss of growth control, defective gene The loss of growth regulators is the reasons for uncontrolled growth. Various forms of cancer causes including: Smoking tobacco, radiation exposure and viral infections. The Gene called p53 is found to be defective in numerous cancer cells. Normally the gene halts the cell cycle until all chromosomes have been replicated. Damaged p53 genes cause cells to NOT respond to signals that would control cell growth.

1.Stem Cells in Medicine 2. Sources of Stem Cells 3. Your Opinion on Stem Cell Research D. Stem Cells: Promises & Problems pg. 253 Stem cells may allow the body to produce replacement cells that have been damaged due to injury or disease. Human embryonic tissue