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?
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
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.
Five Phases of the Cell Five Phases of the Cell CycleCycle
GG11 – 1 – 1stst growth phase growth phase
SS – synthesis – synthesis interphaseinterphase
GG22 – 2 – 2ndnd growth phase growth phase
MM – mitosis – mitosis
CC – cytokinesis – cytokinesis divisiondivision
Interphase - GInterphase - G11 Stage Stage
11stst growth stage growth stage
Cell carries on normal activitiesCell carries on normal activities
Interphase – S StageInterphase – S StageSynthesis stageSynthesis stageDNA is copiedDNA is copied
Two Two identicidentic
al al copies copies of DNAof DNA
Original Original DNADNA
Why does the cell need 2 copies? What would happen if it did not have 2 copies?
Interphase – S StageInterphase – 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 – GInterphase – G22 Stage Stage
22ndnd Growth Stage Growth Stage
Extra organelles & proteins are Extra organelles & proteins are synthesized to prepare for divisionsynthesized to prepare for division
Mitosis: Division of the NucleusMitosis: 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
ProphaseProphaseDNA condenses to form visible chromosomesDNA condenses to form visible chromosomes
Mitotic spindle formsMitotic spindle forms
Nuclear membrane dissolvesNuclear membrane dissolves
MetaphaseMetaphase
Chromosomes Chromosomes line up at the line up at the equator (middle)equator (middle)
AnaphaseAnaphase
Sister Sister chromatids chromatids are pulled are pulled apart by apart by spindle fibersspindle fibers
TelophaseTelophase
Sister chromatids Sister chromatids at opposite polesat opposite poles
Spindle Spindle disassemblesdisassembles
Nuclear envelope Nuclear envelope reformsreforms
CytokinesisCytokinesis
division of the division of the cytoplasmcytoplasm
cell divides cell divides into two into two identical identical daughter cellsdaughter cells