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Transcript
CELLULAR GROWTH Cells grow until they reach their size limitations, then they either stop growing or divide 3 Reasons Why Cells Are Small 1. Surface Area to Volume a. Surface area refers to the area covered by the plasma membrane b. Volume refers to the space taken up by the inner contents of the cell As a cell grows the volume increases more rapidly than the surface area. The surface area to volume ratio decreases. Cells would have difficulty moving materials across the cell. 2. Transport of Substance- Once inside the cell materials move by diffusion and transport proteins. Cells remain small to maximize the ability to transport nutrients and waste products 3. DNA Overload- The ability of the cells to communicate instructions for cellular functions would be harmed if cells were too large. THE CELL CYCLE Once cell becomes too large it must either stop growing or divide. Most cells will eventually divide Prevents cells from becoming too large Is a method for cells to reproduce Provides a method for organisms to grow Provides a method to heal from injuries The end result of the cell cycle is two identical cells Cell Cycle Interphase Interphase—90% of cell cycle S (DNA synthesis) G1 (Cell growth) G2 (growth and preparation for mitosis) Cytokinesis Mitosis Control of Cell Cycle A. Cell Growth G1 checkpoint Determines if the cell is ready to divide B. DNA synthesis G2 checkpoint DNA synthesis is checked C. Mitosis checkpoint Signals the start of First Growth Phase 1. First Growth Phase (G1) cell grows and carries on normal function. Major portion of cell’s life nerves and some muscle cells spend entire life in this phase 2. Synthesis Phase (S) DNA is copied; each chromosome has a pair of chromatids 3. Second Growth Phase (G2) Microtubules are rearranged and preparations made for the nucleus to divide 4. Mitosis Process where the nucleus divides into 2 nuclei and each one has the same number of chromosomes 5. Cytokinesis Process where cytoplasm divides and a new cell is produced