Why Do Cells Need To Why Do Cells Need To Divide?Divide?

It depends on the organismIt depends on the organism Unicellular organisms like bacteria Unicellular organisms like bacteria

(prokaryotes) divide to reproduce(prokaryotes) divide to reproduce Multicellular organisms (most Multicellular organisms (most

eukaryotes) use it to grow larger eukaryotes) use it to grow larger and repair damaged cells.and repair damaged cells.

DifferentiationDifferentiationAll the cells in your body have All the cells in your body have

the same DNAthe same DNAThe fertilized egg (zygote) that The fertilized egg (zygote) that

made you divided many times. made you divided many times. The resulting cells differentiated The resulting cells differentiated

into all the different cell types into all the different cell types you have by turning on certain you have by turning on certain genes in your DNA.genes in your DNA.

3 Types of Cell Division3 Types of Cell Division 1. 1. Binary fission-cell division in Binary fission-cell division in

prokaryotesprokaryotes 2. Cell Cycle (with Mitosis)-cell 2. Cell Cycle (with Mitosis)-cell

division in eukaryotesdivision in eukaryotes 3. Meiosis—cell division to form sex 3. Meiosis—cell division to form sex

cells (egg and sperm)cells (egg and sperm)

ProkaryotesProkaryotes Divide by Divide by binary binary

fissionfission Circular DNACircular DNA Results in two cells Results in two cells

genetically the samegenetically the same What has to take What has to take

place before any place before any cells divide?cells divide?

3 Types of Cell Division3 Types of Cell Division 1. Binary fission-cell division in 1. Binary fission-cell division in

prokaryotesprokaryotes 2. 2. Cell Cycle (with Mitosis)-cell Cell Cycle (with Mitosis)-cell

division in eukaryotesdivision in eukaryotes 3. Meiosis—cell division to form sex 3. Meiosis—cell division to form sex

cells (egg and sperm)cells (egg and sperm)

EukaryotesEukaryotes The Cell CycleThe Cell Cycle

– GrowthGrowth– Repair or replacement of cells.Repair or replacement of cells.– Control size so nutrients can get in and waste Control size so nutrients can get in and waste

can get out in a timely fashioncan get out in a timely fashion Some cells die quickly and need to be Some cells die quickly and need to be

replaced a lot (skin cells).replaced a lot (skin cells). Some cells never get replaced (nerve cells).Some cells never get replaced (nerve cells). Some organisms can regenerate whole body Some organisms can regenerate whole body

parts.parts.

Each cell goes through a Each cell goes through a series of phases series of phases throughout its life.throughout its life.

The The cell cyclecell cycle-all events -all events between one cell division between one cell division and the nextand the next– **ONE REPLICATION & **ONE REPLICATION &

ONE DIVISIONONE DIVISION– Result? 2 daughter cells Result? 2 daughter cells

genetically exact to the genetically exact to the parent cell they came parent cell they came from.from.

2 basic steps: 2 basic steps: Interphase (G1, S, Interphase (G1, S, G2) and Mitosis (M)G2) and Mitosis (M) – Interphase: the Interphase: the

longest part of cell longest part of cell cycle composed of cycle composed of G1, S, G2 stagesG1, S, G2 stages

– M=Mitosis = Nuclear M=Mitosis = Nuclear divisiondivision

First step of InterphaseFirst step of Interphase G1 (G=gap)G1 (G=gap) Cell going through intense growth Cell going through intense growth

using lots of food and energy.using lots of food and energy. DNA at this point is unwound and DNA at this point is unwound and

called called chromatinchromatin

Second step in InterphaseSecond step in Interphase S=Synthesis phase.S=Synthesis phase. All DNA replicated during this phaseAll DNA replicated during this phasecell cell

has double the genetic material has double the genetic material Sister chromatid-Sister chromatid- one of two identical one of two identical

parts of a replicated chromosomeparts of a replicated chromosome

Third step in InterphaseThird step in Interphase G=gapG=gap Cell grows some more.Cell grows some more. Extra organelles are being made.Extra organelles are being made.

After Interphase (G1, S, and G2)After Interphase (G1, S, and G2) M=Mitosis M=Mitosis Mitosis = Nuclear division.Mitosis = Nuclear division. MITOSIS IS MITOSIS IS ONLYONLY THE DIVISION OF THE NUCLEUS DURING THE CELL CYCLE!!! THE DIVISION OF THE NUCLEUS DURING THE CELL CYCLE!!! There are four mitotic steps:There are four mitotic steps:

– ProphaseProphase– MetaphaseMetaphase– AnaphaseAnaphase– Telophase.Telophase.

ProphaseProphase DNA coils up into DNA coils up into

visible visible chromosomeschromosomes

Nuclear envelope Nuclear envelope disappears.disappears.

Spindle fiber forms Spindle fiber forms from the centrioles.from the centrioles.

MetaphaseMetaphase Chromosomes Chromosomes

begin to line up begin to line up at the equator of at the equator of the cell.the cell.

Spindle fibers Spindle fibers attach to the attach to the centromerecentromere of of each sister each sister chromatid of the chromatid of the chromosome.chromosome.

AnaphaseAnaphase Spindle fibers Spindle fibers

begin to pull begin to pull apart sister apart sister chromatids. chromatids. Each is now a Each is now a chromosomechromosome

Spindle Spindle breaks down breaks down after this.after this.

TelophaseTelophase Each side now Each side now

has a full set has a full set of of chromosomes.chromosomes.

Nuclear Nuclear envelope will envelope will reform.reform.

CytokinesisCytokinesis ““Cytokinesis”—division of Cytokinesis”—division of

cytoplasm at the end of cytoplasm at the end of the cell cycle which the cell cycle which cleaves the cell in half.cleaves the cell in half.

Animal cells form a Animal cells form a “furrow.”“furrow.”

Plant cells form a new cell Plant cells form a new cell wall.wall.

Formation of two, Formation of two, identical daughter cells identical daughter cells with 46 chromosomeswith 46 chromosomes

Overall Cell Cycle ProcessOverall Cell Cycle Process IInterphase (G1, S, G2) and Mitosis nterphase (G1, S, G2) and Mitosis

((PProphase, rophase, MMetaphase, etaphase, AAnaphase, naphase, TTelophase) elophase) IPMATIPMAT

Cell Cycle AnimationCell Cycle Animation

REGULATION OF CELL CYCLEREGULATION OF CELL CYCLE Cell division controlled by Cell division controlled by

certain proteins called certain proteins called cyclinscyclins

Cancer cells don’t respond to Cancer cells don’t respond to the cyclin signals---the cyclin signals---uncontrolled growth uncontrolled growth (tumors)(tumors)

Benign tumors stay intactBenign tumors stay intact Malignant tumors spread Malignant tumors spread

throughout body throughout body (metastasize)(metastasize)