Cell Growth and Division

I.Background Info A.Why Do Cells Divide? 1.Growth of organism 2.Repair damaged cells 3.Reproduction in microorganisms

B. Why are cells so tiny? 1. To maximize the surface area to volume ratio. What is the surface area and volume of a 4 cm cube? h w d  Surface Area (SA) = (h) x (w) x (# of sides) 4 x 4 x 6 = cm 2  Volume (V) = (h) x (w) x (d) 4 x 4 x 4 = cm 3 SA/V = /2 or 1.5

What if we cut the cube into eight 2 cm cubes?  Volume 2 x 2 x 2 x 8 = cm 3  Surface Area 2 x 2 x 6 x 8 = cm 2  SA/VOL =

2. Having twice the surface area and the same volume allows for a more efficient exchange of materials (nutrients, wastes, O 2, CO 2 and H 2 O) a) If a cell becomes too large it can’t transport materials across the membrane fast enough 3. DNA “Overload” a) Cell does not make more copies of DNA as it grows; therefore the nucleus is limited in how much cell activity it can control

Cell Size Movie

II. Chromosomes A. Chromosomes (DNA) carry all the genetic information for the organism and are passed on from one generation to the next B. Every species has a specific # of chromosomes (Human = 46, Chimp = 48, Mosquito = 6, Adder’s tongue fern = 1262) C. Made up of chromatin 1. Made of DNA twisted around histone proteins. 2. Compactly folded and coiled to form a chromatid. Why?

Chromosome Supercoils Coils Nucleosome Histones DNA double helix

 Draw Fig pg. 244 D.Prior to division cells must duplicate their DNA Why? E. Two identical “sister” chromatids are formed a) Attached by the centromere

III. The Cell Cycle A. Consists of Interphase and M phase (mitosis and cytokinesis)

III. The Cell Cycle B. Interphase 1. Cell’s nucleus and nucleolus are clearly visible. 2. Chromosomes have not appeared. 3. Consists of 3 phases: a) G 1 phase - cell growth right after cell division b) S phase - DNA replication c) G 2 phase - replication of cell organelles (to prepare for division) and synthesis of cell division structures 4. Cell spends ~90% of its time in interphase

The Cell Cycle Draw Fig. 10-4, pg. 245 M phase G 2 phase S phase G 1 phase

Interphase Movie

C. Mitosis 1. Prophase a. Nuclear membrane, nucleus and nucleolus start to disappear b. Chromosomes are clearly visible and are randomly arranged c. Spindle fibers and centrioles appear (not in plants)

2. Metaphase a. Chromosomes are lined up at the center of the cell (metaphase plate) b. Done by attaching themselves to the visible spindle fibers

3. Anaphase a. The sister chromatids are pulled apart (at the centromeres) to the opposite poles of the cell. b. Each chromatid is a single chromosome. c. Each side gets an exact copy of each chromosome.

4. Telophase a. Nuclear membrane, nucleus and nucleolus reappears. b. Chromosomes and spindle fibers start to disappear. c. Mitosis is complete at this point.

D. Cytokinesis 1. The completion of M phase where cell organelles and cytoplasm are divided into two new cells. 2. In plant cells the Golgi bodies secrete a cell plate in the middle of the cell. Mitosis Video Clip

Centrioles Chromatin Interphase Nuclear envelope Chromosomes (paired chromatids) Prophase Centromere Spindle forming Metaphase Centriole Spindle Centriole Anaphase Individual chromosomes Nuclear envelope reforming Telophase Cytokinesis DRAW Fig. 10-5, pg. 246

Mitosis Movie

IV. Regulating the Cell Cycle A.Controls on Cell Division 1.When cells come into contact with other cells they respond by not growing (density dependent inhibition) 2.Controls on cell growth and cell division can be turned on and off 3.With an injury, cells at edge of injury are stimulated to divide rapidly to begin healing

B. Cell Cycle Regulators 1. Cyclins are proteins that regulate the cell cycle 2. They signal when it is time for a cell to divide, duplicate their chromosomes, or enter another phase of the cycle 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.

C. Cancer 1. Uncontrolled cell growth and division 2. Cells do not respond to regulatory signals 3. Malignant tumors are masses of cells that can damage surrounding tissue 4. When a cancer metastasizes, cells have broken off the tumor and traveled to other parts of the body 5. Known causes are smoking, tobacco, radiation exposure, and certain viruses

V. Stem Cells A. Three to five days after fertilization, a human embryo is a mass of cells called stem cells B. Stem cells are pluripotent, which means they are not specialized and have the ability to differentiate (develop into any specialized cell, e.g. nerve cell)

C. Three current sources: 1. Embryonic stem cells (discarded embryos from fertility treatment) 2. Umbilical cord blood 3. Adult stem cells (bone marrow, heart, brain, lungs) D. Potential Treatments 1. Alzheimer’s disease 2. Heart disease 3. Limb regeneration 4. Organ transplants ml