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  Don’t keep dividing:  Nerve cells  Muscle cells  Do keep dividing:  Skin cells  Digestive tract cells  Bone marrow cells  Blood cells (but wait, they don’t 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