THE CELL THEORY All living things are composed of cells. Cells are the basic units of structure and function in living things. New cells are produced from existing cells.

DNA “overload” – If the cell becomes to large, the information stored in the DNA does not meet the cell’s needs. Surface area to volume ration – Fig – If the cell becomes to large the surface area/volume decreases and the exchange of materials into and out of the cell becomes more difficult.

Chromatid – one of two identical “sister” parts of a duplicated chromosome Centromere – area where the chromatids are attached Centromere Sister Chromatids

Interphase – period of the cell cycle between cell division G 1 – phase in which cells grow, synthesize new proteins and organelles S – phase in which DNA is replicated G 2 – phase in which molecules and organelles required for cell division are produced

Cell Division/M phase (Mitosis & Cytokinesis) Stages of Mitosis include prophase, metaphase, anaphase, and telophase

Nuclear membrane and nucleolus disappear Chromatin condenses into chromosomes Spindle fibers form and centrioles move to opposite poles

Chromosomes attach to spindle fibers Chromosomes line up in the center

Sister chromatids separate and move to opposite poles

Spindle fibers disappear Chromosomes uncoil Nuclear membrane and nucleolus reappear

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The following sites are links to various mitosis quizzes sis.tdf?0 sis.tdf?0

Cytokinesis is the fivision of the cytoplasm, usually occurs during late anaphase/early telophase; each new cell receives one set of chromosomes and half of the organelles – Fig Animal cells form a cleavage furrow Plant cells form a cell plate that develops into a new cell wall

When cells “touch” other cells they stop dividing, therefore, cell division can be turned “on” or “off” – Fig. 10-7

Cell Cycle Regulators 1. cyclins – a family of proteins that regulate the cell cycle; the amount of these proteins the cell cycle; the amount of these proteins rise and fall in time with the cell cycle (Fig. rise and fall in time with the cell cycle (Fig. 10-8) 10-8) 2. Internal regulators – responds to events inside the cell; control when a cell enters inside the cell; control when a cell enters each phase of the cell cycle (cyclins are each phase of the cell cycle (cyclins are examples of internal regulators) examples of internal regulators) Cycle-Cyclins-and-Checkpoints Cycle-Cyclins-and-Checkpoints

Cell Cycle Regulators 3. External regulators – respond to events outside the cell; controls events outside the cell; controls speed of cell cycle speed of cell cycle a. Embryonic cells divide more rapidly than the cells of adults rapidly than the cells of adults b. Certain cell types divide more rapidly than others (see analyzing rapidly than others (see analyzing data pg. 249) data pg. 249)

Cancer – uncontrolled cell growth