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

• Interphasecell is growing and

doing its thing

• MitosisCell division

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

What phase?What phase?

What phase?What phase?

What phase?What phase?

What stages?