Cell DivisionCell Division

ChromosomesChromosomes

Are made of DNAAre made of DNA Each chromosome consists of sister Each chromosome consists of sister

chromatids attached at a centromerechromatids attached at a centromere

Cell CycleCell Cycle

During the cell cycle, a cell grows, During the cell cycle, a cell grows, prepares for division, and divides to prepares for division, and divides to form 2 daughter cells, each of which form 2 daughter cells, each of which then begins the cycle again.then begins the cycle again.

Interphase – time for growth and Interphase – time for growth and regular cell activity.regular cell activity.

Most of a cell’s life is spent in Most of a cell’s life is spent in Interphase.Interphase.

InterphaseInterphase

Introduction to Cell DivisionIntroduction to Cell Division

A time when a cell performs its usual functions, depending on the location in the body.

MitosisMitosis

The division of somatic or regular The division of somatic or regular cells.cells.

Its divided into 4 phases.Its divided into 4 phases. Remember Interphase is NOT part of Remember Interphase is NOT part of

Mitosis.Mitosis.

Introduction to MitosisIntroduction to Mitosis

ProphaseProphase

First stage of MitosisFirst stage of Mitosis Chromatin condenses into Chromatin condenses into

chromosomeschromosomes Centrioles separate and a spindle Centrioles separate and a spindle

fiber begins to form.fiber begins to form. Nuclear membrane breaks downNuclear membrane breaks down

ProphaseProphase

MetaphaseMetaphase

Second Phase of MitosisSecond Phase of Mitosis Chromosomes line up in the middle Chromosomes line up in the middle

of the cell.of the cell. Each chromosome is connected to a Each chromosome is connected to a

spindle fiber.spindle fiber.

MetaphaseMetaphase

AnaphaseAnaphase

Third Phase of MitosisThird Phase of Mitosis The sister chromatids separate into The sister chromatids separate into

individual chromosomes and move individual chromosomes and move apart to opposite ends of the cell.apart to opposite ends of the cell.

AnaphaseAnaphase

TelophaseTelophase

Fourth and Final Stage of MitosisFourth and Final Stage of Mitosis Chromosomes gather at opposite Chromosomes gather at opposite

ends of the cell and lose their distinct ends of the cell and lose their distinct shapesshapes

Two new nuclear membranes have Two new nuclear membranes have formed.formed.

TelophaseTelophase

CytokinesisCytokinesis

The cytoplasm pinches in half.The cytoplasm pinches in half. Each daughter cell has an identical Each daughter cell has an identical

set of duplicate chromosomesset of duplicate chromosomes

Regulating the CycleRegulating the Cycle

A protein called cyclin helps regulate A protein called cyclin helps regulate the cell cycle in eukaryotic cells.the cell cycle in eukaryotic cells.

They respond to internal and They respond to internal and external events. These proteins are external events. These proteins are regulators.regulators.

When Things Go WrongWhen Things Go Wrong

Cancer cells do not respond to the Cancer cells do not respond to the signals that regulate the growth of signals that regulate the growth of most cells.most cells.

As a result, they form masses of cells As a result, they form masses of cells called tumors that can damage called tumors that can damage surrounding tissues.surrounding tissues.

The Cell Cycle in DepthThe Cell Cycle in Depth

InterphaseInterphase Mitotic StageMitotic Stage CytokinesisCytokinesis ApoptosisApoptosis Cell Cycle and CancerCell Cycle and Cancer

INTERPHASEINTERPHASE 3 STAGES3 STAGES

– GG11 stage stage

– S StageS Stage

– GG22 Stage Stage

– Some cells such as nerve and muscle cells Some cells such as nerve and muscle cells typically do NOT complete the cell cycle and typically do NOT complete the cell cycle and are said to have entered the Gare said to have entered the G00 stage. stage.

– For adult mammalian cells, interphase lasts For adult mammalian cells, interphase lasts ~20 hours (90% of cell cycle)~20 hours (90% of cell cycle)

INTERPHASE: GINTERPHASE: G11 stage stage

Stage BEFORE DNA replicationStage BEFORE DNA replication Cell doubles its organelles and Cell doubles its organelles and

accumulates materials for DNA accumulates materials for DNA synthesissynthesis

G used to stand for “gap” but now it G used to stand for “gap” but now it stands for “growth”stands for “growth”– Protein synthesis is a part of these Protein synthesis is a part of these

growth stagesgrowth stages

INTERPHASE: S stageINTERPHASE: S stage

DNA synthesis/replication occursDNA synthesis/replication occurs– Each chromosome is composed of one Each chromosome is composed of one

chromatid (DNA double helix) and chromatid (DNA double helix) and makes 2 sister chromatids (2 identical makes 2 sister chromatids (2 identical DNA double helix molecules)DNA double helix molecules)

INTERPHASE: GINTERPHASE: G22 stage stage

Stage from the completion of DNA Stage from the completion of DNA replication to the onset of mitosisreplication to the onset of mitosis– The cell synthesizes protein that will The cell synthesizes protein that will

assist cell division (i.e. protein found in assist cell division (i.e. protein found in microtubules)microtubules)

M (Mitotic Stage)M (Mitotic Stage)

The cell division stage that includes The cell division stage that includes mitosis (nuclear division) and mitosis (nuclear division) and cytokinesis (division of the cytokinesis (division of the cytoplasm)cytoplasm)

ProphaseProphase

Nucleolus is disappearingNucleolus is disappearing Nuclear envelope is fragmentingNuclear envelope is fragmenting Spindle is forming between Spindle is forming between

centrosomescentrosomes Asters radiate from the centrioles Asters radiate from the centrioles

within the centrosomeswithin the centrosomes

PrometaphasePrometaphase

Kinetochores of sister chromatids Kinetochores of sister chromatids attach to kinetochore spindle fibers attach to kinetochore spindle fibers extending from opposite polesextending from opposite poles

Chromosomes move back and forth Chromosomes move back and forth until they are aligned at the until they are aligned at the metaphase platemetaphase plate

MetaphaseMetaphase

Spindle is fully formedSpindle is fully formed Duplicated chromosomes align at Duplicated chromosomes align at

metaphase platemetaphase plate Spindle consists of polar spindle Spindle consists of polar spindle

fibers that overlap at the metaphase fibers that overlap at the metaphase plateplate

Kinetochore spindle fibers that are Kinetochore spindle fibers that are attached to chromosomes attached to chromosomes

Anaphase

Sister chromatids separate to become daughter chromosomes that move toward the poles

Polar spindle fibers slide past one another

Kinetochore spindle fibers disassemble

Cytokinesis by furrowing begins

Telophase

Nuclear envelopes re-form Chromosomes begin changing back

to chromatin Nucleoli reappear Spindle disappears

Plant CellsPlant Cells

Lack centrioles and astersLack centrioles and asters Mitotic spindle still forms and goes Mitotic spindle still forms and goes

through the same 5 mitotic phasesthrough the same 5 mitotic phases

CytokinesisCytokinesis

In animal cells, it’s a furrowing In animal cells, it’s a furrowing process that divides the cytoplasmprocess that divides the cytoplasm

In plant cells, the formation of a cell In plant cells, the formation of a cell plate from which the plasma plate from which the plasma membrane and cell wall are membrane and cell wall are completedcompleted

The Cell Cycle and CancerThe Cell Cycle and Cancer

Cancer is due to the mutation of Cancer is due to the mutation of genes that control the cell cyclegenes that control the cell cycle

Cancer cells are…Cancer cells are…– Are NondifferentiatedAre Nondifferentiated– Divide repeatedlyDivide repeatedly– Have abnormal nucleiHave abnormal nuclei– Don’t require growth factorsDon’t require growth factors– Not constrained by their neighborsNot constrained by their neighbors

The Cell Cycle and CancerThe Cell Cycle and Cancer

After forming a tumor, cancer cells After forming a tumor, cancer cells metastasize and start new tumors metastasize and start new tumors elsewhere in body.elsewhere in body.

What you can do to try to prevent What you can do to try to prevent cancer…cancer…– Avoid unnecessary radiationAvoid unnecessary radiation– Avoid exposure to organic chemicals Avoid exposure to organic chemicals

(ex: tobacco smoke)(ex: tobacco smoke)– Have a diet rich in fruits and vegetablesHave a diet rich in fruits and vegetables

Prokaryotic Cell DivisionProkaryotic Cell Division

Prokaryotic chromosome has a few Prokaryotic chromosome has a few proteins and a single, long loop of DNAproteins and a single, long loop of DNA

Binary fission- the chromosome attaches Binary fission- the chromosome attaches to the inside of the plasma membrane and to the inside of the plasma membrane and replicates. replicates.

As cell elongates, the chromosomes are As cell elongates, the chromosomes are pulled apartpulled apart

Inward growth of the plasma membrane Inward growth of the plasma membrane and formation of new cell wall material and formation of new cell wall material divide the cell in 2.divide the cell in 2.

Prokaryotic vs. Eukaryotic CellsProkaryotic vs. Eukaryotic Cells

Binary fission (in prokaryotes) and Binary fission (in prokaryotes) and mitosis (in cellular eukaryotic protists mitosis (in cellular eukaryotic protists and fungi) allow organisms to and fungi) allow organisms to reproduce asexuallyreproduce asexually

Mitosis in multicellular eukaryotes is Mitosis in multicellular eukaryotes is primarily for the purpose of primarily for the purpose of development, growth, and repair of development, growth, and repair of tissues. tissues.