The Cell Cycle What is the cell cycle? What is mitosis – or cell division? What happens in each stage?

Cell Cycle Cells grow and divide 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) bacteria brain 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 Mitosis cell is growing and doing its thing Cell division

Five Phases of the Cell Cycle G1 – 1st growth phase S – synthesis interphase G2 – 2nd growth phase M – mitosis C – cytokinesis division

Interphase - G1 Stage 1st growth stage Cell carries on normal activities

Two identical copies of DNA Interphase – S Stage Synthesis stage DNA is copied Two identical copies of DNA Why does the cell need 2 copies? What would happen if it did not have 2 copies? Original DNA

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 – G2 Stage 2nd Growth Stage 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 Prophase Prepare to divide Metaphase Middle Anaphase Apart Telophase The End http://www.cellsalive.com/mitosis.htm

Prophase DNA condenses to form visible chromosomes Mitotic spindle forms Nuclear membrane dissolves

Metaphase Chromosomes line up at the equator (middle)

Anaphase Sister chromatids are pulled apart by spindle fibers

Telophase Sister chromatids at opposite poles Spindle disassembles Nuclear envelope reforms

Cytokinesis division of the cytoplasm cell divides into two identical daughter cells

What phase?

What phase?

What phase?

What stages?