Chapter 10 (pages ) There are 2 limitations that cause cells to divide instead of grow indefinitely With a partner, take a few minutes to think of what these 2 limitations might be! Why do cells divide instead of growing indefinitely? There are 2 limitations that cause cells to divide instead of grow indefinitely Larger the cell, more demands placed on DNA Library Larger the cell, harder to move nutrients and wastes across the cell membrane Volume increases much more rapidly than SA in a growing cell smaller ratio Town Road In eukaryotic cells, chromosomes pass genetic information from one generation to the next Made up of DNA and proteins Not visible to the human eye because the DNA and proteins are spread out through the nucleus, but condense at beginning of cell division We have 46 chromosomes Centromere center attachment Sister chromatids Identical replications of the chromosome Process by which a cell divides into 2 new daughter cells Prokaryotes simple process Eukaryotes bit more complex Prokaryotes do not have organelles or a nucleus to replicate, Eukaryotes do! Interphase: time period between cell divisions G1 phase Cell growth S phase DNA replication Chromosome replication G2 phase Preparation for mitosis Organelle production M phase Includes mitosis and cytokinesis Go phase Cell is done dividing Interphase: period of growth that prepares the cell for division Includes G1, G2, and S phase Cell size increases DNA replication Division of the cell nucleus 4 Phases Prophase Metaphase Anaphase Telophase 1 st and longest phase (takes 50-60% of the total time) Chromosomes become visible Spindle starts to form fanlike microtubule structure that separates the chromosomes Nucleolus disappears and nuclear envelope breaks down Short phase Chromosomes line up across center of cell Microtubules connect the centromere to the 2 poles of spindle Centromeres split, allowing sister chromatids to separate and become individual chromosomes Chromosomes move until they are at opposite ends of the cell Ends when chromosomes stop moving Final phase Chromosomes lose their distinct shape A new nuclear envelope forms around each cluster of chromosomes Cytoplasm pinches in half Each daughter cell has an identical set of duplicate chromosomes A structure known as the cell plate forms midway between the divided nuclei The cell plate gradually develops into a separating membrane A cell wall then begins to appear in the cell plate Cell Plate On a separate sheet of paper answer the following questions: In which phase of mitosis do the chromsomes appear and become visible to the human eye? In which phase of mitosis do the chromosomes line up in the middle of the cell? In which phase of interphase does the DNA replicate? During which phase of mitosis does the nuclear membrane (envelope) reappear? In which phase of mitosis do the centromeres split? In which phase of interphase does cell growth occur? Cellular division in a multicellular organism is a carefully controlled process Not all cells move through the cell cycle at the same rate and some do not continue to divide after development Dont keep dividing: Nerve cells Muscle cells Do keep dividing: Skin cells Digestive tract cells Bone marrow cells Blood cells (but wait, they dont have a nucleus?!) Controlled Cell Growth Scientists have observed controlled cell growth in a lab by using a petri dish with nutrient broth What is a common reason why our cells are stimulated to grow? Skin Cancer Lung Cancer Brain Cancer Bone Cancer Pancreatic Cancer Some cancers have a cause Tobacco Use Radiation Exposure 1 thing in common All cancer has 1 thing in common the cell has lost its ability to control cell division A large number of cancers have been tied to a defect in the p53 gene p53: regulator that halts the process of mitosis until all chromosomes have been replicated If the cell starts dividing too early, it loses valuable info it needs to regulate cell division from there on out Name that phase. Interphase Prophase Metaphase Anaphase Telophase