Cell Growth and DivisionCell Growth and Division

Cell division is needed for…Cell division is needed for…

1. Growth – most organisms grow by 1. Growth – most organisms grow by producing more cellsproducing more cells

2. Cell Replacement2. Cell Replacement

3. Reproduction (asexual)3. Reproduction (asexual)

Cell division must occur because..Cell division must occur because..Cells cannot continue to grow indefinitely.Cells cannot continue to grow indefinitely.There are two main reasons why they cannot:There are two main reasons why they cannot:– 1. A larger cell places more demands on its DNA.1. A larger cell places more demands on its DNA.– 2. A cell’s volume increases faster than its surface 2. A cell’s volume increases faster than its surface

area.area.

Thus, before the cell becomes too large, it Thus, before the cell becomes too large, it divides.divides.

http://www.rogers.k12.ar.us/users/ehutches/cellsize.jpg

Cell division is when a cell divides Cell division is when a cell divides into two new daughter cells.into two new daughter cells.

Step one: Mitosis – division of the nucleusStep one: Mitosis – division of the nucleus

Step two: Cytokinesis – division of the Step two: Cytokinesis – division of the cytoplasmcytoplasm

Cell division is controlled by several Cell division is controlled by several factors:factors:

1. When cells come in contact 1. When cells come in contact with each other, they stop with each other, they stop growing.growing.2. Internal regulators (p53 2. Internal regulators (p53 gene, cyclin) make sure the cell gene, cyclin) make sure the cell doesn’t divide until doesn’t divide until chromosomes have doubled.chromosomes have doubled.3. External regulators are 3. External regulators are growth factors that stimulate or growth factors that stimulate or inhibit growth. inhibit growth. – These prevent organ systems These prevent organ systems

from interfering with each other from interfering with each other during embryonic development.during embryonic development.

http://www.sigmaaldrich.com/img/assets/25160/cyclin-cell_cycle.jpg

World’s Tallest PeopleWorld’s Tallest People

Cancer is uncontrolled cell growth.Cancer is uncontrolled cell growth.

When cells lose control over When cells lose control over growth, a tumor forms.growth, a tumor forms.There are many cause of There are many cause of cancer:cancer:– 1. genetics1. genetics– 2. tobacco2. tobacco– 3 UV light3 UV light– 4. Viral infection (i.e. HPV)4. Viral infection (i.e. HPV)

http://www.researchvegf.com/researchvegf/images/Tumor-progression-1.jpg

http://whyweareready.com/wp-content/uploads/2008/03/brain-tumor.jpg http://www.emoryhealthcare.org/Images/urology_images/Bladder%20tumor1.jpg

The Cell CycleThe Cell Cycle

Cell Cycle – the series of events that cells Cell Cycle – the series of events that cells go through as they grow and divide.go through as they grow and divide.

http://images1.clinicaltools.com/images/gene/celldivision/cellcycle.jpg

Interphase – time in-between cell divisions.Interphase – time in-between cell divisions.– Includes GIncludes G11, S, and G, S, and G22

– Gap 1 (GGap 1 (G11)) – normal growth and protein production– normal growth and protein production

Synthesis (S) – chromosomes (DNA) are copiedSynthesis (S) – chromosomes (DNA) are copiedChromosomes double (humans - from 46 to 92).Chromosomes double (humans - from 46 to 92).The doubled chromosomes are connected by a centromere.The doubled chromosomes are connected by a centromere.

– Gap 2 (GGap 2 (G22) – duplicate organelles and molecules needed for cell ) – duplicate organelles and molecules needed for cell division are made.division are made.

http://www.daviddarling.info/images/centromere.gif

Phases of the Cell CyclePhases of the Cell Cycle

Mitosis – the division of the cell nucleusMitosis – the division of the cell nucleus– Mitosis has 4 phases:Mitosis has 4 phases:

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

IPMATIPMAT– Mitosis results in two genetically identical Mitosis results in two genetically identical

daughter cells.daughter cells.

InterphaseInterphase

Nucleus is still in tact and the nucleolus is Nucleus is still in tact and the nucleolus is visible.visible.

Includes GIncludes G11, S, and G, S, and G22

ProphaseProphase

Chromatin Chromatin condenses into condenses into chromosomes.chromosomes.Centrioles Centrioles separate and separate and spindle fibers form.spindle fibers form.The nucleus The nucleus (envelope) and (envelope) and nucleolus break nucleolus break down (no longer down (no longer visible).visible).

http://www.houghtonmifflinbooks.com/booksellers/press_release/studentscience/gif/mitosis1.gif

MetaphaseMetaphase

Chromosomes Chromosomes line up at the line up at the center of cell.center of cell.

Each Each chromosome is chromosome is attached to a attached to a spindle fiber at spindle fiber at the centromere.the centromere.

AnaphaseAnaphase

The sister The sister chromatids are chromatids are pulled apart pulled apart (centromere (centromere splits) to opposite splits) to opposite ends of the cell.ends of the cell.

TelophaseTelophase

Nuclear Nuclear membrane and membrane and nucleolus nucleolus reform.reform.

Mitotic spindle Mitotic spindle disappears.disappears.

Nuclear division Nuclear division is complete.is complete.

CytokinesisCytokinesis

Pinching of the cytoplasm, resulting in Pinching of the cytoplasm, resulting in two genetically identical cells.two genetically identical cells.