The Cell Cycle What is the cell cycle? What is mitosis – or cell division? What happens in each stage?
Cell Cycle Cells grow and dividedivide Why do you think cells need to stay relatively small?
Why can’t cells just keep growing and growing?
Most cells are small because Large cells place large demands on DNA – the DNA can’t “keep up” Large cells have trouble exchanging nutrients and wastes through the cell membrane – material has to travel too far
On the other hand… REALLY small cells like bacteria cells are not able to have specialized parts (organelles) bacteriabrain cell
The advantages of being larger (or multicellular) Can SPECIALIZE!!!
When will a cell divide? The surface area: volume ratio limits cell size. If a cell gets too big, it must divide to survive. If a cell gets too big, it will undergo mitosis.
Cell Cycle Interphase cell is growing and doing its thing Mitosis Cell division
Five Phases of the Cell Cycle G 1 – 1 st growth phase S – synthesis interphase G 2 – 2 nd growth phase M – mitosis C – cytokinesis division
Interphase - G 1 Stage 1 st growth stage 1 st growth stage Cell carries on normal activities Cell carries on normal activities
Interphase – S Stage Synthesis stage Synthesis stage DNA is copied DNA is copied Two identical copies of DNA Original DNA Why does the cell need 2 copies? What would happen if it did not have 2 copies?
Interphase – S Stage Why does the cell need 2 copies? What would happen if it did not have 2 copies when it got ready to divide?
Interphase – G 2 Stage 2 nd Growth Stage 2 nd Growth Stage Extra organelles & proteins are synthesized to prepare for division Extra organelles & proteins are synthesized to prepare for division
Mitosis: Division of the Nucleus Used for growth and repair Occurs in somatic (body) cells Produces two new cells identical to the parent
Mitosis – 4 stages P rophase P repare to divide M etaphase M iddle A naphase A part T elophase T he End
Prophase DNA condenses to form visible chromosomes DNA condenses to form visible chromosomes Mitotic spindle forms Mitotic spindle forms Nuclear membrane dissolves Nuclear membrane dissolves
Metaphase Chromosomes line up at the equator (middle) Chromosomes line up at the equator (middle)
Anaphase Sister chromatids are pulled apart by spindle fibers Sister chromatids are pulled apart by spindle fibers
Telophase Sister chromatids at opposite poles Sister chromatids at opposite poles Spindle disassembles Spindle disassembles Nuclear envelope reforms Nuclear envelope reforms
Cytokinesis division of the cytoplasm division of the cytoplasm cell divides into two identical daughter cells cell divides into two identical daughter cells
What phase?
What stages?