Cellular Reproduction (Eukaryotes) Biology - Chapter 9 Pages

Warm-up: 1.How would you describe the process by which organisms increase in size? 2.Are the cells of a small plant smaller or larger than those of a large plant? 3.Why do cells stay small?

What we will learn in Chapter 9: - Living things grow by producing more cells. - Cells produce other cells by dividing. - The process by which a cell divides into two new daughter cells is called cell division. Why must cells divide? Why don’t they just grow bigger?

Three Reasons Why Cells Divide: 1.Growth 2.Replace 3.Repair

The key factor that limits the size of a cell is the ratio of its surface area to its volume. plasma membrane cytoplasm and its contents the structure through which all nutrients and waste products must pass. By remaining small, cells have a higher ratio of surface area to volume and can sustain themselves more easily.

1 um 2 um 4 um On your own, calculate the volume of surface area to volume for each of the cells below. Explain why it is best for cells to remain small. (see pages )

-Once a cell reaches its size limit, it either stops growing or it divides. THE 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 - divides into two daughter cells which each begin the cycle again.

Three Main Stages of The Cell Cycle: (See page 246, Figure 9.3) I. Interphase II. Mitosis III. Cytokinesis

I. Interphase: -The phase in which a cell spends most of its life. There are three sub-stages: 1. G1 (Gap 1) – cell grows and performs normal functions. 2. S (Synthesis) – cell replicates its DNA in preparation for cell division. 3. G2 (Gap 2) – cell takes inventory to make sure it is ready to continue on to mitosis.

II. Mitosis: Stage in which the cell’s nucleus and nuclear material divides and separates to opposite ends of the cell. FOUR STAGES OF MITOSIS: 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

1. Prophase: First stage of mitosis. Stage of mitosis in which a dividing cell spends the most time. Chromatin condenses into chromosomes: chromosome centromere sister chromatids hill.com/sites/ /student_view0/chapter 11/animations.html

2. Metaphase: Shortest phase of mitosis. Chromosomes attach to mitotic spindles (aka. spindle fibers) and align along the equator of the cell.

3. Anaphase: Microtubules shorten moving chromosomes to opposite poles and the chromatids are pulled apart.

4. Telophase: Chromosomes reach poles of cell and begin to relax or de-condense. Nuclear envelope reforms. Nucleolus reappears. CELL IS ALMOST DONE DIVIDING!

III. Cytokinesis: Cell pinches inward at “equator” until the cell divides into two daughter cells with identical nuclei. In animal cells, this happens at the cleavage furrow (formed during cytokinesis). In plant cells, instead of pinching, the cell plate is formed.

Cleavage Furrow (animal cells) Prophase

Cell Plate (plant cells)

On-line Onion Root Tip Lab vities/cell_cycle/36m.html vities/cell_cycle/36m.html GIVE IT A TRY!!!

Cell Cycle Regulation The timing and rate of cell division are important for cells to develop normally. Proteins called CYCLINS and CDK enzymes control the cell cycle. These proteins take action at certain checkpoints to make sure the cell cycle is functioning properly. If errors are found, often they are repaired / /

Cancer: Abnormal Cell Cycle Cancer is the uncontrolled growth and division of cells. Caused by mutations in the regulatory genes that were not repaired during the cell cycle at the checkpoints. NIH Student Activities

Cancer Genetics More than one change in DNA is required to change an abnormal cell into a cancer cell. This could explain why cancer runs in some families. These changes cause a person to have a predisposition for cancer.

Apoptosis: (programmed cell death) -This “death program” can become activated and cause a cell to shrink, shrivel and die in a controlled manner. -Examples: - the fetal development of a human hand/foot (webbed). -Cell’s DNA damaged beyond repair. -Leaves of deciduous trees fall during autumn.

Stem Cells: Unspecialized cells that can develop into specialized cells when placed under the right conditions. 2 Types: – Embryonic stem cells (ethical concerns) – Adult stem cells (not as controversial)

Stem Cell Research is Underway: Alzheimer's, cerebral palsy, paralysis, diabetes, and people who suffer damage to their heart after a heart attack.

Binary Fission