Chapter 10 Cell Growth and Division. I.Cell Growth A. A living thing grows because it produces more and more cells. 1. The cells of a human adult are.

Chapter 10 Cell Growth and Division

I. Cell Growth

A. A living thing grows because it produces more and more cells.

1. The cells of a human adult are no larger than the cells of a human baby, but there are more of them.

2. The smaller the cell the better it is. The larger the cell the more difficult to perform cellular functions.

3. Cell division is the process whereby the cell divides into two daughter cells.

B. Rates of cell growth

1. Cells can grow very fast.

2. Bacteria cell growth is called- binary fission.

3. Bacteria will grow and grow and then split in half into two identical cells.

4. The amazing thing with cellular division is how accurate it is.

5. Before a cell can get too large, a growing cell divides forming two daughter cells.

6. The process by which a cell divides into two new daughter cells is called cell division.

II. Cell Division

A. The first stage of cellular division in Eukaryotes is called mitosis. The second stage is called cytokinesis.

B. Chromosomes

1. In Eukaryotic cells, chromosomes carry the genetic information that is passed on from one generation of cells to the next.

2. Chromosomes are made up of DNA, which carries the cells coded genetic information- and proteins.

3. The cells of every organism have a specific number of chromosomes.

4. Example- the cells of fruit flies have 8 chromosomes and that of a human has 46 chromosomes.

5. Chromosomes are not visible in most cells except during cell division.

6. Well before cell division, each chromosome is replicated, or copied.

7. Because of this, each chromosome consists of two identical, “sister” chromatids.

8. Each pair of chromatids is attached to an are called the centromere. They are like the “twist tie” that holds the chromosomes together.

C. The cell cycle

1. The cell cycle describes the life of a Eukaryotic cell.

2. The cell cycle is a repeating sequence of cellular growth and division during the life of an organism.

3. A cell spends 90% of its time in the first three phases of the cycle-Interphase.

4. First growth (G1)phase- a cell grows rapidly and carries out its routine functions. Cells that are not dividing remain in the G1 phase.

5. Synthesis (S) phase- A cell’s DNA is copied during this phase. At the end of this phase, each chromosomes consists of two chromatids attached at the centromere.

6. Second growth (G2) phase-In the G2 phase, preparations are made for the nucleus to divide.

7. Mitosis- The process during cell division in which the nucleus of a cell is divided into two nuclei.

8. Cytokinesis- the cytoplasm splits.

D. The cell cycle is carefully controlled.

1. If a cell spends 90% of its time in interphase, how do cells “know” when to divide?

2. Cell Growth (G1) checkpoint-This checkpoint makes the key decision of when the cell will divide or not.

3. DNA synthesis (G2) checkpoint-DNA replication is checked at this point by DNA repair enzymes. If this checkpoint is passed, proteins help to trigger mitosis.

4. Mitosis check point- will trigger the exit from mitosis.

E. Mitosis

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Interphase (not really a phase)ProphaseMetaphaseAnaphaseTelophaseCytokinesis

INTERPHASE Interphase- is part of the cell cycle

before mitosis. During Interphase • The cell grows• DNA is being copied• This period between cell division can be very

long.

INTERPHASE

PROPHASE Prophase- This is the longest

phase. During this phase;• The nuclear envelope disappears.• The centrioles start to move to the opposite

poles.• Spindle fibers start to form.• Chromosomes are becoming evident.

PROPHASE

METAPHASE Metaphase-Metaphase is the

shortest phase of mitosis.• The chromosomes line up in the middle of

the cell.

METAPHASE

ANAPHASE ANAPHASE- Begins when the

centromere that join the sister chromatids start to split.

• The chromosomes are being pulled to the opposite sides of the cell toward the Centrioles.

ANAPHASE

TELOPHASE TELOPHASE-Final process of

mitosis.• Chromosomes are at the opposite poles.• Nuclear envelope reforms.

TELOPHASE

CYTOKINESIS-Splitting of the cytoplasm.

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III. Regulating the Cell Cycle

A. Controls on cell division.

1. Scientists can observe the effects of controlled cell growth in the lab by placing some cells in a petri dish.

2. On the bottom of the dish is nutrient agar, which is food for the cells.

3. Most cells will grow until they form a thin layer covering the bottom of the dish. (see page 250) Then the cells stop growing.

4. If cells are removed from the center of the dish, they will again grow until the space is filled.

5. The same thing happens in the body to repair from an injury.

B. Cell cycle regulators.

1. For many years scientists are looking for something that can regulate the cell cycle.

2. It was discovered that a protein cyclin regulated the cell cycle.

3. Cyclin regulate the timing of the cell cycle in Eukaryotic cells.

4. It was also discovered that there are two types of regulator proteins 1- those that occur inside of the cell and 2- those that occur outside of the cell.

C. Internal regulators

1. Proteins that respond to events inside the cell are called internal regulators.

2. Internal regulators that allow the cell cycle to proceed only when certain processes have happened inside of the cell.

D. External regulators

1.      Proteins that respond to events outside the cell are called external regulators.

2. External regulators direct ells to speed up or slow down the cell cycle.

3.       Growth factors are among the most important external regulators.

 4. They stimulate the growth and division of

cells.

5. Growth regulators are very important in embryonic development and wound healing.

E. Uncontrolled cell growth.

1.      Why is cell growth regulated so carefully?

2.      Cancer is a consequence of uncontrolled cell growth.

3. Cancer is a disorder in which some of the body’s own cells lose the ability to control growth

4. Cancer cells do not respond to the signals that regulate the growth of most cells.

5. As a result, they divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.

6. Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.

7. There are certain carcinogens that can cause this to happen. Such as: tobacco, radiation exposure, and even a viral infection.

8. Cancer is a disease of the cell cycle, and conquering cancer will require a much deeper understanding of the processes that control cell division.

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