Chapter 10 Cell Growth & Division

10-1 Cell Growth Nutrient use/waste production depends on surface area of cell Because volume increases much quicker than surface area, a cell increasing in size would have problems with input and output Smaller cells are able to produce enough mRNA to make adequate proteins

Surface Area to Volume Surface Area = L x W x 6 (where 6 is the number of sides) Volume = L x W x H Example: Side is 3 cmSide is 2 cm SA = 54 cm 2 SA = 24 cm 2 Volume is 27 cm 3 Volume is 8 cm 3 Ratio of SA to V is 2:1 Ratio of SA to V is 3:1

Cell Division One cell divides into two daughter cells when resources run out Cells must replicate DNA prior to division so each new cell is identical New cells increase the surface area so input/output problems are corrected & DNA overload is avoided

10-2 Cell Division: Mitosis & Cytokinesis Two stages of cell division Mitosis- Nucleus of a cell is divided into two nuclei with identical chromosomes as the parent cell Cytokinesis- Cytoplasm divides forming two new cells

Chromosomes Contain genetic information in the form of DNA (Humans have 46 total chromosomes) Made of chromatin which is made of DNA and protein

DNA DNA (which has strands that are much longer than chromosomes) is coiled around proteins called histones forming beadlike structures called nucleosomes The result is the tightly packed fibers that make up chromosomes After DNA replication, the chromosomes condense and can be seen as two pair of chromatids attached at the centromere

Cell Cycle A period from the beginning of one mitosis to the beginning of another Comprised of M phase - mitosis (the period of division) and interphase (a period of nondivision during which the cell grows and prepares for division) Interphase: G1 – gap 1 (growth and activity) S- DNA synthesis G2 – gap 2 (growth and activity

10-3 Regulating the Cell Cycle Cells of the skin, digestive tract, bone marrow and blood divide rapidly Most nerve cells do not divide at all New cells develop to replace old, worn out cells

Controls on Cell Division Cells will continue to divide until they come in contact with other cells When an injury occurs such as a cut in the skin or break in a bone, cells at the edge are stimulated to divide rapidly

Cell Cycle Regulators In the early 1980’s two scientists (U.K. & U.S.) found a protein that when injected into a nondividing cell caused a spindle to form and the cell to enter mitosis They called the protein cyclin Since then, more cyclins have been discovered

Uncontrolled Cell Growth Cancer cells do not respond to the signals that regulate the growth of most cells Form masses called tumors